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Summary The finding of dramatically depressed levels of C4 in a 17-year old patient with severe systemic lupus erythematosus (SLE) prompted a genetic study of her family. This study revealed the existence of a partial C4 deficienty; we found the presence of a C4A3, C4BQo haplotype which was transmitted by the mother to each of her children. This patient possessed, in her serum, an autoantibody with anti-C4 specificity. The immunochemical characterization of this autoantibody revealed that it was IgM and belonged to the immunoconglutinin family. We have studied the effects of this autoantibody on the formation and dissociation kinetics of classical C3-convertase.

Particulate and Triton X-100 solubilized receptors for luteinizing hormone (LH) in the pig and bull testis were studied. In some of the experiments tissue from the rat testis was included for comparison. LH receptors in the bull and pig revealed very similar association and dissociation kinetics, affinity (Kd = 1.2-1.8 x 10(-10) M), stability and physicochemical properties. Binding capacity was higher in the pig (73 fmol/mg protein) than in the rat (33 fmol/mg protein) and bull (17 fmol/mg protein). Hormone binding stabilized the receptor against thermal denaturation and temperature stability decreased upon solubilization. It is concluded that the properties of the testicular LH receptor of the pig and bull are very similar to those previously described from the rat.

Dissociation kinetics were determined at 0°C for molybdate-stabilized glucocorticoid-receptor complexes in rat thymus cytosol. Exposure of complexes to dextran-coated charcoal had no effect on their chromatographic properties or transformation status, but dissociation rates measured after charcoal treatment were significantly lower than those determined by displacement with excess competing steroid. The dissociation rate of the [2,4,6,7- 3 H]prednisolone-receptor complex was similarly modified by chromatography on Lipidex 1000, but not by chromatography on Sephadex G-25 or G-75. It is concluded that treatment of glucocorticoid-receptor complexes with dextran-charcoal or Lipidex 1000 brings about a change in dissociation rate as a consequence of the removal of a lipid component from the complex.

Mammary gland cytosols exhibit temperature-dependent interconversion of cAMP-dissociation rates from low to high affinity (k-1 = 0.14 min-1 at 0 degree C to k-1 = 0.02 min-1 at 24 degrees association). This interconversion corresponds to a change from a site 2 to a site 1 cAMP-dissociation rate for the type II cAMP-dependent protein kinase in mammary gland cytosols. This report presents data which indicates a requirement for MgATP in the temperature-dependent interconversion of cAMP-dissociation rates. The effect of MgATP on the generation of the high affinity state was observed at 24 degrees C but not 0 degree C association. The effect of MgATP was not mimicked by equimolar MgAMP-PNP, but did require an intact type II protein kinase holoenzyme which can undergo autophosphorylation of its regulatory subunit. The effect of MgATP was reproduced with partially purified preparations of beef heart type II protein kinase. These results suggest that MgATP may act through autophosphorylation of the type II holoenzyme. The data suggest a novel role of MgATP in the regulation of cAMP binding to cAMP-dependent protein kinase II.

We have identified and isolated two forms of insulin receptor from rat-liver plasma membranes. The smaller (Mr = 90k) is a single polypeptide. The same poly-peptide appears to be the insulin-binding site of the largerMr = 280k). Only the larger, multisubunit, receptor shows high-affinity binding of insulin and negative cooperativity in its dissociation kinetics.

1. In the rat striatum sulphated CCK8 has no significant effect on equilibrium binding of 3 H-spiperone but has a considerable, although transient, effect under non-equilibrium conditions. 2. Under non-equilibrium conditions (during the association phase of ligand binding) and at high ligand concentrations (1 nM), CCK8 displaces specific binding and at low ligand concentrations (0.1 nM) CCK8 enhances specific binding. 3. CCK8 has no effect on 3 H-spiperone dissociation kinetics.

Constantes de vitesse de formation et de dissociation des complexes de Ca, Sr et Ba des cryptands 2 B •22 et 2 B •2 B 2, dans l'eau en fonction de la temperature

An in vitro transcription assay was used to measure the relative occupancy, sequence specificity, and dissociation kinetics of six actinomycin D binding sites on DNA during conditions of active transcription of the DNA from the lac UV5 promoter. Five of the sites contained a GpC sequence, with three of these having a common AGCT sequence that differed by up to an order of magnitude in affinity for the drug, as indicated by their relative occupany and dissociation kinetics. Positive cooperativity was observed by higher occupancy and slower dissociation kinetics for neighboring GpC sites on a different DNA fragment (UV5-lambda PL). Termination of transcription was observed at some drug binding sites, while complete drug-induced termination of transcription was seen 7-10 nucleotides downstream of two drug sites. This delayed termination was minimized when ITP was incorporated into the transcripts and suggests that a time delay is required to enable stable RNA hairpin helices to form. A model is presented of the role of RNA hairpin helices in delayed, drug-induced termination of transcription. The classical picture of DNA-binding drugs as inhibitors of transcription now appears too simplistic as it does not accommodate this phenomenon. It will be important to gain a greater understanding of the mechanism of this phenomenon of drug-induced termination of transcription, as there are many implications for the design of DNA-acting drugs.

Bioreceptors can provide the basis for specific and sensitive biosensors. There are many sources of bioreceptors in nature for biochemicals of interest in biotechnology and biomedicine. These bioreceptors (antibodies, enzymes, membrane proteins, binding proteins) can be modified and produced in large quantities using modern biotechnological techniques. The characteristics of the biosensor can also be fine-tuned by modifying the structure of the analog-analyte, which will also provide several orders of magnitude of range sensitivity with a given bioreceptor. The ultimate sensitivity of the biosensor may be limited by the dissociation kinetics of the reaction between analyte and bioreceptor because there is a trade-off between sensitivity and sensor response rate to changes in analyte concentration.

A specific polarisation fluoroimmunoassay for the measurement of paracetamol levels in serum has been developed for use in emergency toxicological screening. It is based on the use of a fluorescein-labelled analogue and a sheep antiserum and exploits the rapid dissociation kinetics of the hapten-antibody complex to enable the label and antiserum to be combined as a single reagent. Paracetamol levels are determined by adding 5 μL of serum to 1·5 mL of the single reagent, incubation at ambient temperature for a few minutes and measurement of fluorescence polarisation. In addition to its speed and simplicity, the assay is both accurate and precise and the results obtained correlate closely with those from the commonly used chemical and enzymatic techniques.

TMB-8, a putative inhibitor of intracellular calcium mobilization, prevents the binding of the muscarinic ligand N-[3H]methylscopolamine. The inhibition was observed in four tissues from guinea pig; cortex, heart, pancreas, and ileum, representing Ml, cardiac M2, glandular M2, and heterogeneous M2 subtypes of muscarinic receptors, respectively. The Ki values for all four tissues were approx. 4 μM. However, dissociation kinetics revealed that TMB-8 interacted with an allosteric site of three muscarinic receptor subtypes but not the subtype from pancreas. These results indicate that TMB-8 interacts with muscarinic receptors, and therefore would disrupt calcium mobilization or any second messenger system coupled to these receptors.

[ 3 H]ouabain, bound to Na + , K + -ATPase in the presence of ATP, Mg 2+ + Na + ( complex I ) or in the prescence of Mg 2+ + inorganic phosphate ( complex II ), was more stable when beef heart rather than rabbit heart was the enzyme source. For both species, complex II was more stable than complex I . Unlabeled ouabain in the wash-off medium did not affect drug dissociation kinetics, but did cause inhibition of enzyme activity, suggesting ouabain exchange.

The 6th International Conference on Chemical Materials and Process, 2-4 July 2020, Warsaw, Poland Summarization: The scope of this study is to define the rates under which multi-component gas hydrates contained in the pore space of a mud volcanos' (MV) sediments may decompose in gas and water phase as a result of pressure decrease or temperature increase. Such cases can be encountered during retrieval and handling of pristine samples from the sea floor, or due to an increase of hot mud fluxes from underneath the MV area. Both of the aforementioned shifts of conditions have been studied in the bulk liquid phase of a reactor, while pressure decrease has also been studied in a piston vessel containing artificial sediment at the Centre for Gas Hydrates Research, HW University, Edinburgh. The results indicate that gas hydrate dissociation progresses much faster with pressure decrease than with temperature increase. Moreover, depressurization at temperatures above 15°C causes higher dissociation rates in comparison to that at lower temperatures. Presented on: Journal of Physics: Conference Series

Rigorous computation of the metal flux crossing a limiting surface of a system that contains a mixture of 1 : 1 metal complexes under steady-state planar diffusion in a finite domain and under excess of ligand conditions predicts, for some cases, an enhancement of the metal flux with respect to that expected in a system with independent complexes. Indeed, the coupling of the dissociation kinetics of both complexes can yield higher metal fluxes than expected with important environmental implications. By using the voltammetric techniques AGNES and stripping chronopotentiometry, this paper provides experimental evidence of this enhancement for two systems: Cd/NTA/glycine and Cd/NTA/citric acid. The flux measured in both cases is in good agreement with the flux computed for the global system, exhibiting maximum enhancement ratios above 20%. Theoretical discussion of the flux enhancement factors and of the conditions for this enhancement are also provided.

A zero-dimensional Direct Simulation Monte Carlo (DSMC) model is developed for simulating reacting gas mixtures including state-to-state vibrational kinetics and simple bimolecular reactions. The method is applied to the simulation of three systems: translational relaxation of a hard sphere gas, vibrational relaxation of an anharmonic oscillator gas and dissociation in a simplified H 2 –Xe system. In this last case, the role of translational non-equilibrium is shown to be important in affecting the dissociation kinetics.

Electron stimulated desorption (ESD) in combination with LEED, TPD and AES measurements has been used to investigate the adsorption and decomposition of NO2 on Pt(100). The two modifications of the Pt(100) surface (unreconstructed (1 × 1) and reconstructed (5 × 20) phase) were found to play an important role in the adsorption and decomposition behavior of NO2 on Pt(100). It is shown that the decomposition of molecularly adsorbed NO2 on the reconstructed surface does not follow simple dissociation kinetics. On the basis of our results we suggest an autocatalytic reaction in which the substrate phase transition (5 × 20) → (1 × 1) accelerates the NO2 decomposition.

We present a quantitative model for the irreversible dissociation kinetics of cooperatively bound nonspecific protein–nucleic acid complexes. The model assumes that the major pathway of dissociation is via singly contiguously bound protein that “peels” off the ends of clusters of bound protein. It should therefore be most applicable for proteins that bind nucleic acids with high cooperativity (w > 103). Furthermore, the model assumes that no redistribution of bound protein occurs during the time course of the dissociation. Solutions to the rate equations are presented for the entire time course of the dissociation. Under initial conditions such that the nucleic acid is less than fully saturated with protein, a single-exponential decay is predicted (if w is large). However, when the nucleic acid lattice is initially fully saturated, zero-order kinetics, corresponding to a constant rate of protein dissociation, is predicted. The experimental observation of zero-order dissociation kinetics in a cooperative protein–nucleic acid system is a good qualitative indicator for the dissociation mechanism discussed here. A discussion of the analysis of experimental data that enables one to extract molecular rate constants is presented. Furthermore, comparisons are made between the nonredistributing model presented here and Epstein's model [Epstein, I. R. (1979) Biopolymers18, 2037–2050] in which protein can translocate infinitely quickly while bound to the nucleic acid, and hence protein clusters redistribute during dissociation and maintain an equilibrium distribution on the nucleic acid at all times.