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Conformation-based stimuli-responsive sensors utilize a wide range of macromolecules (referred to as probe in this manuscript) and read-out methods. The review focuses on the variables associated with the mechanistic confirmation change centered around two transduction outputs: electrochemical and fluorescence resonance energy transfer. The electrochemical readout is limited in that the responsive material is bound between the electrode surface and an electroactive tag; interaction with analyte changes the distance between the electrode surface and the electroactive tag. Variables discussed in electrochemical stimuli-responsive sensor outputs include redox tag choice, electrode surface packing density, probe architectures, and redox tag location. Fluorescence resonance energy transfer readout uses a solution-free polymer distance where a conformational change induces a change in distance between a donor fluorophore and an acceptor fluorophore, thereby affecting the degree of nonradiative energy transfer from the donor to the acceptor. Variables discussed in fluorescence resonance energy transfer readouts include fluorophore types and sensor architecture. While there are already many examples of this in the literature, we believe this to be a fertile area for further development.

This chapter introduces micro- and nanostructured piezoelectric polymeric materials, their main physicochemical properties, processing conditions, and applications. In particular, their mechanical to electrical transduction characteristics, flexibility, and easy processability provide those materials with suitable characteristics to be used in sensor and actuator applications. Some representative applications of the materials are presented to highlight the potential of micro- and nanostructured piezoelectric materials.

The lateral interactions model, dedicated to random and non-random distributed electroactive species on redox responsive self-assembled monolayers (SAM), was extended to interactions between redox and non-redox species. This approach supports an unusual result achieved in the field of electrochemical transduction without covalent links between redox and complexant units in mixed SAM. Keywords: Self-assembled monolayers, Cyclic voltammetry, Lateral interactions, Redox interactions, Non-redox interactions

Fundamental concepts are presented of the biochemical and biophysical mechanisms that underlie the transduction and utilization of the transmembrane proton (and sodium) electrochemcial potential gradient generated in the energy-transducing chloroplast thylakoid membranes of oxygenic photosynthesis and the inner membranes of eukaryotic mitochondria. Fundamental features are described of the atomic structures of many of the participating electron and proton transport protein complexes in these membranes.

Biological energy conservation in general is the common expression for all processes how living cells use the free energy of chemical reactions to drive the endergonic synthesis of compounds used as an energy store within the cell. Evolution selected and conserved a unique process of primary energy transduction and conversion found in all kingdoms building the tree of life, the archaea, the bacteria, and the eucarya. This fundamental process occurs via formation of electrochemical potential gradients accross membranes. The primary driving reactions comprise fermentations, anaerobic or aerobic respirations, and oxygenic and anoxygenic utilization of light. The article gives a condensed survey on mechanisms and their catalysts as found in bacteria and archaea.

This chapter gives an overview of the conduction mechanisms in semiconducting metal oxide (SMOX) sensing films and their impact on the transduction of surface chemistry into a measurable sensor signal (relative change of resistance). Following general discussion on the functioning of sensors based on SMOX porous, sensing films, modeling of the conduction in p- and n-type materials is performed. The theoretical results explain why the sensor signals are lower for p-type oxides when compared with n-type oxides. The modeling concepts are verified by applying them to experimental results obtained with sensors based on both n- and p-type SMOXs with good results. In combination with the modeling results, further experiments in more realistic conditions (exposure to CO in humid air) demonstrate that also in these conditions the switch between conduction mechanism controlled by surface depletion layer to one controlled by surface accumulation layer may occur.

Publisher Summary This chapter discusses acoustic transduction. The chapter focuses on cellular aspects of acoustic transduction in the auditory periphery. It is mentioned that information on the function of the mammalian cochlea is derived from experiments performed on preparations from the vestibular labyrinth of mammals, birds, and amphibians, and from the cochlea of birds. The chapter discusses several concepts, including inner ear structure of mammals, cell physiology of endolymph homeostasis and cell physiology of acoustic transduction. Cell physiology of endolymph homeostasis further discusses composition, stria vascularis, and outer sulcus epithelium. The cellular bases of hearing in the auditory periphery were described with emphasis on the sensory hair cells and on cells of the stria vascularis. The latter is a complex structure responsible both for the generation of a lumen-positive electrical potential and for the secretion of potassium to an unusually high level in the cochlear lumen. Transduction of sound waves into neural impulses by the hair cells relies on modulation of an electric current carried by potassium flowing through the hair cells. The ion channels, carriers, and pumps in the marginal cell membranes, which accounts for constitutive potassium secretion are described in the chapter. A wide variety of extracellular and cytosolic signaling pathways that regulate the rate of potassium secretion are also described. The specializations of hair cell physiology are discussed, including the transduction channel in the sensory cilia and the highly unusual lateral membrane motors of OHCs. The description of the physiological mechanisms employed by inner ear epithelial cells is related in the chapter to the function of the organ as a whole.

Excitation–contraction coupling in skeletal muscle is a fast signal transduction process by which depolarization of the sarcolemmal membranes is coupled to the opening of Ca 2+ release channels on the sarcoplasmic reticulum (SR). This transduction occurs at specialized triad junctions and is mediated by two key proteins – the t-tubule dihydropyridine receptor (DHPR)/Ca 2+ channel and the SR ryanodine receptor (RyR) channel. The DHPR and RyR1 associate with other junctional proteins to form a macromolecular complex which spans the triad junction and interacts to control RyR opening. This interaction produces a fast transient rise in [Ca 2+ ] i which activates the contractile proteins and results in muscle contraction.

Publisher Summary This chapter surveys the research on the direct electron transfer (DET) between biomolecules and electrodes for the development of reagentless biosensors. Both the catalytic reaction of a protein or an enzyme and the coupling with further reaction have been used analytically. For a better understanding, a description of electron-transfer processes of redox proteins at electrodes is presented. The chapter characterizes the behavior of the relevant proteins and enzymes at electrodes and discusses their respective biosensors. The sensors for superoxide, nitric oxide, and peroxide are described in the chapter. For biosensors of the third generation, DET to small-redox proteins show interaction with reactive (oxygen) species, while enzymes in direct electric contact are suitable for reagentless-metabolite measurement.

Heme proteins form the cornerstone for our understanding of the general phenomena of molecular cooperativity; where the binding affinity of diatomic ligands in hemoglobin and associated changes in quaternary structure with ligation state is the best-characterized example. At the heart of this problem is an understanding how the initially localized reaction forces couple to the global protein coordinate to execute these functionally relevant motions. The energetics for this process are derived from one or a few chemical bonds and at the instant the bond is formed or broken, the motions are necessarily localized over atomic length scales at the active site and subject to quantum effects. From a practical standpoint, the heme proteins provide ideal model systems for studying the relationship between protein structure and function since they are well-characterized and their ligands can be photo-dissociated with unit quantum efficiency on the truly femtosecond timescale. This chapter discusses the results of ultrafast pump-probe spectroscopy of carboxymyoglobin (MbCO) to determine the initial structure changes of the ligand dissociation process using pulses of less than 10 fs in the 500-600 nm spectral regions.

This chapter deals with the general paradigms of signal perception and transduction in eukaryotic systems and the unique features of signaling in plants. Extracellular signals by 7TM receptors and transduction of the signal via heterotrimeric G-proteins may occur in plants. It is indicated by the presence of sequences that encode putative 7TM proteins, and Gα, Gβ, and Gγ proteins. The phosphoinositide pathway is operative in plants, inositol-l,4,5-triphosphate (IP 3 ) is produced, and Ca 2+ is abundant in plants, but the other second messengers, cyclic AMP (cAMP), cyclic GMP (cGMP), diacylglycerol, and phosphatidyl serine, and the protein kinases, A, G, and C, that they activate seem to be present only sporadically and in modest amounts. In resting cells, levels of cytosolic free calcium, [Ca 2+ ] cyt , are maintained at relatively low levels, but when activated, these levels rise sharply, although transiently. The changes in [Ca 2+ ] cyt are brought about by the combined activities of a variety of channels and pumps.

Publisher Summary This chapter describes the key role of mitochondria in energy transduction in the brain, with particular emphasis on mitochondrial oxidative phosphorylation and electron transfer. It focuses on how brain mitochondria contribute to age-related changes. The possible contribution of oxidative stress to brain aging is also examined. The brain occupies only 2% of the total body weight. However, the cerebral tissue consumes at least 20% of the total oxygen intake by the body at rest. Indeed the brain has an active oxidative metabolism because it derives almost all of its energy from aerobic metabolism. A series of molecular complexes, consisting of various equipotential subunits located in the mitochondrial inner membrane, provide both the transduction of oxidative energy in protonmotive force and the use of proton energy in ATP synthesis. The key mitochondrial enzyme cytochrome oxidase may be assumed as a metabolic marker for neuronal activity. Mitochondria play a key role in energy metabolism, as they carry out oxidative phosphorylation.

Publisher Summary Nutrients provide bacterial cells with the two essential components for sustaining live: matter and free energy. The transduction of matter and free energy between catabolism and anabolism is indirect, which ensures high metabolic flexibility. Nutrients are degraded to more general applicable molecules that serve as multipurpose “building blocks” in biosynthesis. Two major forms of free energy, usually referred to as “metabolic energy,” are intermediate between catabolism and anabolism: adenosine triphosphate (ATP) and ion gradients across the cell membrane. ATP represents a pool of chemical free energy that is released upon hydrolysis. The ion gradients represent free energy stored in an electrochemical gradient of either H+ or Na+. The free energy in the ATP pool and the H+ and Na+ ion gradients is termed metabolic energy and is available to the cell for energy consuming processes. Generation of metabolic energy refers to metabolic processes by which the free energy in these pools increases. The different pools of free energy are convertible through the action of reversible ATPases/synthases that couple the transport of either H+ or Na+ to the hydrolysis/synthesis of ATP.

This chapter discusses the cellular creatine kinase system in contractile tissue. Extracellular creatine (Cr) is sequestered into the cytosol by a sodium driven co-transport system from where it is phosphorylated by the intracellular isoenzymes of creatine kinase (CK). Discussion of extracellular creatine use for improving cellular energy transduction requires an understanding of the role of this system. The findings of numerous investigators since the mid-1970s support the role of the CK circuit as an integrated system of energy supply and energy consumption in cardiovascular tissue. It is clear that when Cr enters the cell via the specific Cr transporter rapid phosphorylation by the CK reaction takes place. The resultant PCr is utilized by the cell for essential metabolic processes. The CK system plays a role in both energy transduction and signal amplification in cardiovascular tissue.

Protein molecular organization on solid matrices has intensively been explored in various manners. Although most of these researchers have not paid attention on retainment of protein functions, this chapter focuses on artificially designed protein organizates which are capable of molecular recognition and molecular information transduction. Redox enzymes have been assembled in a monolayer on the solid surface by a potential-assisted self-assembling method as well as a thiol-gold self- assembling method. These enzymes are electronically communicated with the solid substrate through a molecular interface of conducting polymer and a covalently bound mediator. Electron transfer type of enzyme sensors have been fabricated by the self-assembling methods. Calmodulin has been hybridized with phospho diesterase with retaining its activity to respond to calcium ion in changing its conformation so as to activate phospho diestelase. Intelligent molecular materials have been designed using calmodulin. An ordered antibody array has also been assembled on the solid surface by a combination of Langmuir Blodgett (LB) film method and self-assembling method. An ordered monolayer of protein A is deposited on the solid surface by LB method, which is followed by self-assembling of antibody. Individual antigen molecules which are complexed with the antibody array have been quantitated selectively by atomic force microscopy (AFM).

Publisher Summary The low temperatures and high hydrostatic pressures of the deep ocean directly affect the structure and function of all the proteins and membranes of ectotherms. The environment is thus an important selective force shaping the evolution of organisms in this extensive habitat. This chapter examines the effects of hydrostatic pressure on one important membrane-associated function, the transduction of an extracellular message into an intracellular second message. A number of approaches have been employed to identify and define at the molecular level the effects of pressure on transmembrane signaling, both on the components in isolation and on the entire functional complex. The effects of pressure have been compared in three cold-adapted species, which are common at different depths and hence experience different pressure regimes. These teleost species have been useful models for studies of pressure adaptation. The membrane system studied, the A1 adenosine receptor was chosen as a representative G protein-coupled receptor and because of its occurrence in teleost brain and the range of pharmacological tools available for its study.

Publisher Summary The response of a fungus to osmotic stress involves the integrated function of many components of cell metabolism. The dehydration stress is countered by an important mechanism that entails accumulation of polyols, primarily glycerol, to achieve an internal environment that is conducive for enzyme function and growth under water stress. The changes in the composition of the cytoplasm are controlled by systems for biosynthesis of polyols and for transport of inorganic ions. The intracellular retention of glycerol is controlled at the level of glycerol efflux and by systems for glycerol uptake. The osmoregulatory processes require energy to drive transport and carbon supply for polyol formation. The capacity for substrate uptake under osmotic stress and the efficiency operating the osmoregulatory processes are important in setting the limits for growth at low water potentials. The fungal response to changes in the external water potential must involve sensing as well as transduction of the received signal. Combined genetic and physiological analysis is required for a deeper understanding of fungus-water relations. Analysis at this level has revealed sequential induction of osmotically controlled genes in enteric bacteria and given exciting insights in signal transduction and regulation of the process.

This chapter describes enzyme-based fiber optic sensors. Enzymes are most useful reagents that allow selective sensing of biologically important species, including enzyme substrates, metabolites, inhibitors, activators, and others. The chapter provides an overview of how enzymatic reactions can be monitored by making use of optical chemical sensors. The chapter also describes new types of biosensors in which the intrinsic fluorescence of a co-substrate (NADH) or co-enzyme (FAD) changes as a result of the enzyme/substrate interaction. The FAD-based system has the advantage of accepting oxygen as a second substrate. As a result, it acts fully reversibly in the presence of oxygen. Moreover, its excitation and emission wavelengths are in the visible. These findings have led to new types of optical biosensors in which the holo-enzymes act as both the recognition and transduction elements. Because carbon dioxide is the end product of aerobic metabolism and enzymatic activity always is associated with the existence of life, it became obvious to incorporate a CO 2 sensor into a device for detection of bacterial contamination of blood.

Publisher Summary Knowledge of the structure of biological membranes can provide a basis for understanding their functional role at a molecular level. The detailed enzymatic steps involved in processes such as the active transport of ions across otherwise impermeable membrane bilayers, the passive gating actions of ion channels, energy transduction processes (oxidative phosphorylation), light energy ion gradient transduction, and receptor/channel regulatory processes require the knowledge of both the biochemical and biophysical properties of a membrane. The correlation of a specific biochemically characterized event with an associated structural event can help in the understanding of the way biological membranes function. Methods for ordering and orienting membranes should (1) preserve the functionality of a membrane—in particular, the enzymatic or biological processes it performs, (2) not alter the inherent structure of the membrane—in particular, the conformation of proteins, and (3) where possible, be verified by other techniques to ensure that a proper order and/or orientation has been achieved.

Publisher Summary This chapter discusses the role of calcium (Ca)-binding proteins in signal transduction. Measurement of the free intracellular calcium [Ca 2+ ] within cells suggests that it is very low, of the order of 10–100 nM. This means that the vast majority of intracellular Ca is bound. Considering that the extracellular Ca concentration is about 1 mM (compared to 10 nM [Ca 2+ ] i ) and that the interior of the cell is negatively charged there is a large electrochemical gradient driving Ca ions into the cell, however the relative impermeability of the plasma membrane to Ca ions prevents large movements of Ca ions across the plasma membrane. The Ca transient is controlled by the uptake and release of Ca across the three major membrane systems which border the cytoplasm—the plasma membrane, the inner mitochondria1 membrane, and the endoplasmic reticulum. Each membrane possesses distinctive transport mechanisms which act in concert to regulate and modulate intracellular Ca. Cellular signal transduction can be divided into two separate components: (1) the generation of an intracellular signal from an external event and (2) transduction of the intracellular signal into the physiological response of the cell.

Publisher Summary Bacteria require for growth and survival chemical free energy, which is derived from catabolic substrates. In phototrophic bacteria light energy can be the main source of this chemical free energy. The energy supplied by these energy sources is usually not directly applied for the synthesis of cell material, or for other energy requiring processes, but is first translated into other forms of metabolic energy. Generally, three main types of “metabolic energy intermediates” can be distinguished. With these energy intermediates, energy-requiring metabolic processes can be driven and/or the energy can be transduced into other energy intermediates. These three main metabolic energy intermediates are phosphorylation potentials, redox potentials , and transmembrane (e1ectro)chemical potentials. The important role of transmembrane electrochemical potentials is to serve as metabolic energy intermediates. This chapter discusses the current notion of energy flow in bacteria with special emphasis on the regulation exerted by the components of the three main free energy intermediates on the microbe's metabolism.

Publisher Summary This chapter describes the preparation and properties of the enzymes and enzyme complexes of the mitochondrial oxidative phosphorylation system. The enzymes concerned with electron transport from NAD(P)H and succinate to molecular oxygen, energy conservation and transduction, and adenosine triphosphate (ATP) synthesis and hydrolysis are located in the mitochondrial inner membrane. Systematic fractionation of this membrane has shown that these enzymes are contained mainly in five protein–lipid complexes. This results in precipitation of complexes I, II, and III, which are separated by centrifugation from complex V in the supernatant. Then, the binary complex I–III is separated from II–III by precipitation with ammonium acetate, and finally I–III and II–III are resolved and separated into I, II, and III, using cholate and ammonium sulfate. The fractionation procedure involves the use of deoxycholate and cholate in conjunction with KCI, a neutral salt of low ionic strength, for membrane solubilization, and of ammonium acetate and ammonium sulfate for precipitation of the desired fragments.

Publisher Summary This chapter discusses the mechanisms of energy transduction. The chapter focuses on the “proton circuit,” that links the generators and utilizers of proton electrochemical potential in the chemiosmotic scheme. Energy-conserving (or energy-transducing) membranes possess the two classes of proton-pumping complex that are together required for the transduction of respiratory or photosynthetic energy into energy stored as ATP, or more precisely in the form of a displacement of the reactants and products of the ATPase reaction from equilibrium. The energy transducing membranes are the plasma membrane of prokaryotic bacteria and blue-green algae, the inner membrane of mitochondria, and the thylakoid membrane of chloroplasts. The ATP synthase, called the proton-translocating ATPase, is present in closely similar forms in all energy-transducing membranes. When the complex is assembled in the membrane it catalyzes a hydrolysis or synthesis of ATP that is coupled to the obligatory translocation of protons across the membrane. The nature of the second proton-pumping complex in each membrane is dependent on the primary energy source utilized by the organelle.

Publisher Summary This chapter describes various protein–chromophore interactions that serve as spectroscopic and photochemical determinants. Studies on pigment spectra have demonstrated that appropriately positioned charged or polar amino acids are responsible for producing the colors of visual pigments. Electrostatic interactions also appear to play an important role in the light transduction mechanism. A related problem, not considered in this work, concerns the nature of the photoisomerization in the excited state of the chromophore. The quantum yield for this process is 0.67 in the pigments, an order of magnitude greater than the solution value. It is not unlikely that the same charges responsible for wavelength regulation and energy storage play a catalytic role in the photochemistry. Electrostatic interactions are believed to play a central role in many enzyme mechanisms) and it is to be expected that their relative contribution will be even greater in the low dielectric medium provided by the interior of membranes. Thus, the emphasis on these factors in membrane proteins such as rhodopsin and bacteriorhodopsin is not unwarranted.

Publisher Summary This chapter discusses the structure and function of protein complexes in the photosynthetic membrane. Photosynthetic membranes of cyanobacteria, algae and plants contain four major protein complexes that harness light energy and convert it into chemical energy. Two of these protein complexes, the cytochrome b 6 -f complex and the proton-ATPase (adenosine triphosphate) complex, contain no pigments and function in biochemical reactions. The other two, photosystem PS I reaction center and PS II reaction center, function in photochemical reactions and contain pigments involved in light-harvesting and primary energy transduction. There are a few ways to define membrane protein complexes. Because a minimal structure is usually difficult to resolve, copurification of various polypeptides was taken as a primordial criterion for the integrity of those polypeptides as part of the protein complex. Cyt b-c complex forms the evolutionary link between the respiratory and photosynthetic electron-transport pathways. In both systems, it oxidizes quinols and reduces metalloproteins while generating proton motive force. In cyanobacteria, the Cyt b 6 -f complex is shared by both respiration and photosynthesis. The biogenesis of the Cyt b 6 -f complex is not controlled by light, in contrast to the biosynthesis of the two reaction centers. Etiolated leaves contain substantial amounts of Cyt b 6 -f complex and the relative amounts of the various subunits did not significantly change during the light-dependent greening of etiolated seedlings. During growth, additional complexes were assembled by a concerted mechanism in which all the four subunits were synthesized and assembled at the same rate.

Publisher Summary This chapter discusses the hydrogen and electrons successively transfer through a number of oxidation–reduction carriers ultimately to oxygen. Energy derived from the reaction is utilized by the organism through energy coupling and transduction. The chapter discusses the mitochondrial hydrogen and electron transfer that occur in the inner membrane. The sequence of hydrogen and electron transfer can be deduced from the results of thermodynamic and kinetic studies. The former alone cannot determine the path; both concentrations of the components and the so-called energy barrier (activation energy) must also be considered. Results from kinetics are perhaps most direct and reliable. The reliability of the results is, needless to say, dependent upon the accurate selection of wave lengths used without interference by other substances present. The determinations of relatively rapid reactions possess some practical difficulties, even with special instruments.

Publisher Summary The biologically important processes of respiratory-chain phosphorylation and of photophosphorylation involve the transduction of redox or light energy, respectively, for the synthesis of ATP from ADP and P i against an energy gradient. In chemical or physical processes, a continuous entropy production occurs. It is this entropy change that may be considered as the irreversible component of such processes. Mitochondria are the subcellular organelles that catalyze the synthesis of ATP from ADP and phosphate, coupled to the oxidation of substrates by molecular oxygen. They consist of an outer membrane that allows free permeation of all low-molecular weight solutes, an extensively folded inner membrane that functions as the energy transducer, and an inner space. Energy transduction from light to ATP in chloroplasts is catalyzed by the membranes of the grana stacks or thylakoids. These thylakoid membranes contain light-harvesting pigments, reaction centers, carotenoids, redox components, and an ATPase complex comparable to that of mitochondria

Publisher Summary Life on earth is dependent upon the conversion of light energy to chemical energy by plants. Since 1960, it has been generally accepted that plants contain two photosystems: photosystem I (PSI) and photosystem I1 (PSII), which are intimately and co-operatively involved in the process of light energy transduction and are located in the thylakoid membranes of the chloroplasts. This chapter reviews the ways in which photosystems may interact and examines the possible consequences of such interactions on thylakoid function. Sufficient background information is provided to allow a sensible perspective of photosystem interactions to be developed. To understand the nature and functions of the photochemical apparatus and the potential mechanisms for regulating the photochemical processes, the characteristics of the thylakoid membranes are considered. It is apparent from the preceding discussions that knowledge of the composition and organization of the thylakoid membrane has advanced enormously in recent years and demonstrated the potential for many interactions between intrinsic pigment-containing, macromolecular complexes. However, the physiological significance of such interactions has not been satisfactorily resolved. This is especially true of the interactions between complexes that result in modifications in excitation energy distribution between PSI and PSII.

Publisher Summary This chapter discusses methods for measuring protonmotive force (PMF) and the motility that is the consequence of its use. The best-studied type of bacterial motility derives from the use of external flagella. The external flagellar filaments are thin helical structures that themselves perform no transduction of metabolic energy into mechanical work. They are rotated by motors at their base, and their rotation generates thrust. The motors are reversible, and it is this that permits control of behavior, as the reversal probability is controlled by the environment. It should be noted that PMF can, under some circumstances at least, play a role in controlling the “switching” of the flageilar motor. Major examples of this are aerotaxis and phototaxis, which appear to be more strictly “PMF taxis.” Another related aspect is pH taxis and certain classes of repellent-induced taxes, where perturbation of either internal or external pH is responsible for affecting motor switching.

Publisher Summary Muscle is a highly integrated chemical machine. One of the most impressive aspects of this integration is the ability to increase the rate of energy utilization by approximately 2500-fold within milliseconds. This efficient transduction of chemical into mechanical energy occurs through the subtleties of the interactions of myosin, actin, adenosine 5'-triphosphate (ATP), and inorganic ions. These interactions may be controlled or influenced by some of the minor proteins of the myofibril (tropomyosin B, troponin, and possibly aactinin). From a classic point of view, the proteins of muscle may be categorized into stromal (connective tissue for support), sarcoplasmic (glycolytic enzymes and pigments), and myofibrillar (contractile) protein fractions. The sarcoplasmic portion, a readily solubilized complex protein material, occupies all the spaces of the muscle cell, not taken up by formed elements, and the contractile system. Although, it is unlikely that any of the sarcoplasmic proteins enter into contraction, they nevertheless change in quantity during continued function or training and undoubtedly penetrate the myofibril; consequently, it would be dangerous to completely dismiss the possibility of the participation or involvement of a minor component (excluding the known involvement of the sarcotubular system) of this fraction in the contractile system. The proteins that exist in concert in the myofibril are vital to in vivo function and play dominant functional roles in the fabrication of protein foods. This chapter is concerned principally with: Molecular features of proteins in the myofibrils of skeletal muscles of mammals, preparative procedures for isolating and purifying these proteins, applied considerations relevant to their use in food systems, and the essentiality for relating present knowledge of the biological aspects of myofibrillar proteins to their potential use in fabricated food systems.

A citrate transport system in B. subtilis was studied as the first step in investigation of trans-membrane transport by gram-positive bacteria. The possibility of isolating clean membranes together with genetic methods (transduction and transformation) seems to make B. subtilis an ideal organism for this work. However, no transport system had yet been well characterized in this organism. Citrate was chosen after a preliminary survey because it has an active transport system whose activity could be increased by induction. Induction kinetics were typical, activity of the transport system rising sharply after a few minutes' lag. Furthermore, the system could be gratuitous, that is the cells were unaffected by the consequences of transport in an aconitase-negative mutant growing in rich medium. This mutant formed the transport system at a high level in the absence of added citrate, owing to the accumulation of endogenous citrate. The maximal velocity was high, 145 μmoles/min/g dry weight of cells at 37°C and KM (2.3 mM) was large. An extensive series of inhibitor studies was carried out to determine the specificity of the system. It was found to be limited to several di- and tri-carboxylic acids, fundamentally ones related to malate. The activity of the transport system was largely retained by protoplasts. Membrane vesicles' activity was much reduced (200-fold) but so also was serine transport activity. Hence, citrate transport probably resides in the membrane, and it does not include an essential, easily released component such as a binding protein. The high KM of the system precluded direct binding measurements. The role of phospholipid synthesis in creation of the citrate transport system was studied in a glycerol-requiring mutant deprived of glycerol. Induction continued for at least a half-hour; during this period the cells did not synthesize phospholipids de novo . Thus, B. subtilis does not need net glycerol-lipid synthesis in order to incorporate the citrate transport system into its membrane. Properties of this system are briefly compared with those for transport of di- and tri-carboxylic acids in other organisms.

Publisher Summary Photosynthetic organisms use the energy of light quanta to convert the inorganic compounds carbon dioxide and water to the organic compounds required for survival by all other living organisms. Thus, the transformation of the energy of light quanta into oxidants and reductants useful for chemical synthesis assumes central importance in biology. In the sequence of events that begins with the absorption of light and culminates in the vast array of organic compounds characteristic of living organisms, chlorophyll plays a crucial role. The chlorophylls constitute a small family of closely related pigments long recognized as the primary photo-acceptors of photosynthetic organisms. Most of what is known or inferred about the function of chlorophyll in the plant is based on absorption and fluorescence spectroscopy in the visible. Consequently, an appreciation of the nuances of chlorophyll electronic transition spectra both in vitro and in vivo is essential. In all photosynthetic organisms, the main long wavelength absorption band in the red is due to chlorophyll