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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.

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.

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 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.