Hydrogenases are microbial enzymes that catalyze the reversible oxidation of molecular hydrogen and play a vital role in anaerobic energy metabolism. Ni-Fe hydrogenases have a metal center in which the iron carries two cyanide (CN) and one monoxide (CO) moieties as ligands. Because of their toxicity in the free state, the source and biosynthesis of the CO and CN ligands is of considerable importance, but little has been known about this pathway. In the February 14 Science, Stefanie Reissmann and colleagues at the University of Munich, Germany, show that the biosynthesis of the cyanide ligands follows a previously unknown pathway (Science, 299:1067-1070, February 14, 2003).

Several auxiliary proteins are known to be required for the synthesis of the metal center of active NiFe-hydrogenases. Of these proteins, HypF — which accepts carbamoyl phosphate as a substrate — and HypE are directly involved in the biosynthesis of the...

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