Description:
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Numerous recent developments in the biochemistry, molecular biology, and physiology of formate and H
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metabolism and of the [NiFe]-hydrogenase (Hyd) cofactor biosynthetic machinery are highlighted. Formate export and import by the aquaporin-like pentameric formate channel FocA is governed by interaction with pyruvate formate-lyase, the enzyme that generates formate. Formate is disproportionated by the reversible formate hydrogenlyase (FHL) complex, which has been isolated, allowing biochemical dissection of evolutionary parallels with complex I of the respiratory chain. A recently identified sulfido-ligand attached to Mo in the active site of formate dehydrogenases led to the proposal of a modified catalytic mechanism. Structural analysis of the homologous, H
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-oxidizing Hyd-1 and Hyd-5 identified a novel proximal [4Fe-3S] cluster in the small subunit involved in conferring oxygen tolerance to the enzymes. Synthesis of
<jats:italic>Salmonella</jats:italic>
Typhimurium Hyd-5 occurs aerobically, which is novel for an enterobacterial Hyd. The O
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-sensitive Hyd-2 enzyme has been shown to be reversible: it presumably acts as a conformational proton pump in the H
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-oxidizing mode and is capable of coupling reverse electron transport to drive H
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release. The structural characterization of all the Hyp maturation proteins has given new impulse to studies on the biosynthesis of the Fe(CN)
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CO moiety of the [NiFe] cofactor. It is synthesized on a Hyp-scaffold complex, mainly comprising HypC and HypD, before insertion into the apo-large subunit. Finally, clear evidence now exists indicating that
<jats:italic>Escherichia coli</jats:italic>
can mature Hyd enzymes differentially, depending on metal ion availability and the prevailing metabolic state. Notably, Hyd-3 of the FHL complex takes precedence over the H
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-oxidizing enzymes.
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