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Photosynthetic organisms adopt two different strategies for the reduction of the C17 = C18 double bond of protochlorophyllide (Pchlide) to form chlorophyllide a, the direct precursor of chlorophyll a (refs 1-4). The first involves the activity of the light-dependent Pchlide oxidoreductase (5-9), and the second involves the light-independent (dark-operative) Pchlide oxidoreductase (10) (DPOR). DPOR is a nitrogenase-like enzyme consisting of two components, L-protein (a BchL dimer) and NB-protein (a BchN-BchB heterotetramer), which are structurally related to nitrogenase Fe protein and MoFe protein, respectively (10,11). Here we report the crystal structure of the NB-protein of DPOR from Rhodobacter capsulatus at a resolution of 2.3 Å. As expected, the overall structure is similar to that of nitrogenase MoFe protein: each catalytic BchN-BchB unit contains one Pchlide and one iron-sulphur cluster (NB-cluster) coordinated uniquely by one aspartate and three cysteines. Unique aspartate ligation is not necessarily needed for the cluster assembly but is essential for the catalytic activity. Specific Pchlide-binding accompanies the partial unwinding of an α-helix that belongs to the next catalytic BchN-BchB unit. We propose a unique trans-specific reduction mechanism in which the distorted C17-propionate of Pchlide and an aspartate from BchB serve as proton donors for C18 and C17 of Pchlide, respectively. Intriguingly, the spatial arrangement of the NB-cluster and Pchlide is almost identical to that of the P-cluster and FeMo-cofactor in nitrogenase MoFe-protein, illustrating that a common architecture exists to reduce chemically stable multibonds of porphyrin and dinitrogen., Chlorophylls are tetrapyrrole pigments essential for photosynthesis. An asymmetric conjugated double-bond system of chlorophyll a, crucial for efficient light absorption, is formed in the penultimate step of the biosynthetic pathway [...]

The synthesis and anion binding properties of B[F.sub.2] complexes of [beta]-tetraethyl-substituted Ketonesare described with and without electron-withdrawing ethoxycarbonyl moieties at pyrrole [alpha]-positions. The substituents at pyrrole rings of these acyclic anion receptors have played a main role in controlling not only the polarization of binding sites (NH and CH) but also the relative stabilities of the preorganized conformations and the degrees of sterical repulsion.

The synthesis and anion binding properties of B[F.sub.2] complexes of [beta]-tetraethyl-substituted dipyrrolyldiketones are described with and without electron-withdrawing ethoxycarbonyl moieties at pyrrole [alpha]-positions. The substituents at pyrrole rings of these acyclic anion receptors have played a main role in controlling not only the polarization of binding sites (NH and CH) but also the relative stabilities of the preorganized conformations and the degrees of sterical repulsion.

We have determined the atomic structure of the bacteriochlorophyll c (BChl c) assembly in a huge light-harvesting organelle, the chlorosome of green photosynthetic bacteria, by solid-state NMR. Previous electron microscopic and spectroscopic studies indicated that chlorosomes have a cylindrical architecture with a diameter of [approximately equal to] 10 nm consisting of layered BChl molecules. Assembly structures in huge noncrystalline chlorosomes have been proposed based mainly on structure-dependent chemical shifts and a few distances acquired by solid-state NMR, but those studies did not provide a definite structure. Our approach is based on [sup.13]C dipolar spindiffusion solid-state NMR of uniformly [sup.13]C-labeled chlorosomes under magic-angle spinning. Approximately 90 intermolecular C-C distances were obtained by simultaneous assignment of distance correlations and structure optimization preceded by polarization-transfer matrix analysis. It was determined from the [approximately equal to] 90 intermolecular distances that BChl c molecules form piggybackdimer-based parallel layers. This finding rules out the well known monomer-based structures. A molecular model of the cylinder in the chlorosome was built by using this structure. It provided insights into the mechanisms of efficient light harvesting and excitation transfer to the reaction centers. This work constitutes an important advance in the structure determination of huge intact systems that cannot be crystallized. spin diffusion | distance analysis | photosynthesis | antenna complex | excitation transfer

Research has been conducted on the dioxygen-binding non-heme diiron protein hemerythrin. The preparation of the dinucleating bis(carboxylate) ligand dibenzofuran-4,6-bis(diphenylacetate) as a synthetic model for the dioxygen-binding non-heme diiron protein hemerythrin is discussed.

Research has been conducted on the (mu-oxo)bis(mu-carboxylato)diiron(III) complex. The substitution of two methanol ligands by a bidentate hfac (super)- anion is described.

A family of peroxo-bridged diiron (II) complexes was synthesized which matched exactly the combination of carboxylate and imidazole donors of the Hperoxo intermediate in the catalytic cycle of soluble methane monooxygenase. X-ray crystallographic methods were used to investigate and clarify their structures. These studies furnish the most accurate compositional models of the Hperoxo intermediate reported to date and are discussed.

A study on the possibility that the psg gene in Rhodospirillum rubrum contains a 3,4-desaturase and that its disruption produces nonnatural carotenoids is presented. The Rhodospirillum ST4 mutant with a single Tn5 lesion has been isolated wherein a latent branching of the biosynthetic pathway has been discovered. The unnatural carotenoids may have been produced by the incorporation of a cryptic branch in the linear pathway for spirilloxanthin biosynthesis. Results show that the ST4 mutant is a good system for studying the role of carotenoids in bacterial photosynthesis.

The bis(pseudohalide) complexes (Fe2O(mu-XDK)(bpy)2(NCS)2) (1), (Fe2O(mu-XDK)(bpy)2(NCSe)2) (2) and (Fe2O(mu-XDK)(bpy)2(N3)2) (3) (XDK = the dianion of m-xylylenediamine bis(Kemp's triacid imide), bpy = 2,2'-bipyridyl) were synthesized. They were investigated by X-ray crystallography and UV-vis, IR, resonance Raman and Mossbauer spectroscopy. Compounds 1 and 3 were observed to model structural and spectroscopic characteristics of the isothiocyanate- and azide-bound derivatives of methemerythrin, respectively.

A study was conducted on the production of poly(3-hydroxyalkanoic acid) (PHA) from carbon dioxide using two approaches. In the first method, PHA biosynthetic genes accumulating PHA from low-molecular-weight organic compounds were introduced into a hydrogen-oxidizing bacterium. In the second method, the chemolithoautotrophic growth ability of a hydrogen-oxidizing bacterium was introduced into a PHA-producing bacterium. Both approaches proved to be unique and effective in carbon dioxide recycling.

Experimental study enables the assignment of hyperfine-shifted signals of the paramagnetic 1H NMR spectra of Co(II)-substituted Cys112 Asp azurin from Pseudomonas aeruginosa for all the coordinated groups. Spectral studies show little or no localization of unpaired spin density on Met 121 protons of the Cys112 Asp protein. The interpretation of electronic absorption and NMR data is confirmed by a computerized model that visualizes Asp112 and His117 in the ligation sphere and the presence of Gly45 carbonyl and His46.

Circular dichroism spectra of the self-assembled porphyrins which showed intense Cotton effects are mirror-images for the two 31-enantiomers and proved that the supramolecular chirality is dependent on the configuration at the 31-stereocenter. Friedel-Crafts conditions at short reaction times with high concentrations of catalyst and at 0-4 degree [Celsius] was used to perform diacylation of copper 10, 20-bis(3,5-di-tert-butylphenylporphyrin) to obtain 3,17-diacyl-substituted porphyrins, out of the 12 possible regioisomers.

Molecular dynamics (MD) simulations are used for calculating the extra energy with respect to the hexagonal crystal orientation. They have confirmed that dislocations to accommodate the mismatch between hcp-Co alloy nanograins sitting on adjacent slopes of grooves on textured magnetic recording hard disk media has induced the preferred in-plane crystalline orientation.

A simple synthetic route for converting chlorophyll(Chl)-a to bacteriochlorophyll(Bchl)-c is described. Separation of methyl bacteriopheophorbide (MBPhe)-c, transesterification of the 17-propionate group and magnesium insertion successfully led to naturally occurring BChl-c.

The study presents a complete characterization of the resultant chromosomes that are formed by the isotopic replacement of their pigments and lipid from Chlorobium limicola. The analysis shows that the reassembled chlorosomes have similar and longer morphological structures and are found in the same excited-state dynamics in the pigment assembly.

How the bacteriochlorophyll (BChl) c molecules are assembled in the aggregate of an isomeric mixture from Chlorobium limicola in the solid state, as determined by intermolecular [sup.13.C]-[sup.13.C] dipolar correlations, and how the assembly of BChl c in a large aggregate in the solid state compares to, or contrasts to, those in the smaller aggregates in suspension are considered. Results reveal that the structure of the solid-state aggregate of BChl c contains both types of stackings, the dimer-based stacking and the (pseudo) monomer-based stacking.

The excited-state dynamics of chlorosomes from Chlorobium tepidum, upon excitation above the Soret state, was examined by pump-and-probe time-resolved absorption spectroscopy in the subpicosecond to millisecond time region. It is observed that the relaxation processes that accompany the dissipation of the excited-state and the thermal energies vary depending on the time range and the amount of photons supplied.

A study was conducted to characterize synthetic frameworks of the deoxy and oxy forms of the non-heme dioxygen-binding protein hemerythrin by synthesizing an asymmetric (mu-hydroxo)bis(mu-carboxylato)diiron(II) complex. Results indicated that the dinucleating dicarboxylate ligand supports the preparation and synthesis of new iron complexes with structural and spectroscopic properties of deoxy- and oxyHR.

Analysis of the electronic absorption spectrum of gold(I)-substituted wild-type Pseudomonas aeruginosa apoprotein (azurin) reveals a Au(I)-centered 5d to 6p transition in the trigonal Au(I)N2S (N2 = His46, His117; S = Cys112) complex. The complex is considerably distorted as evident from the wide emission band. The blue shift band for the Au(I) Met121Gly protein corresponds to an axial interaction in the binding-site cavity. With the reduction in the excited state distortion, the emission band is narrowed.