The CO and CN- ligands to the active site Fe in [NiFe]-hydrogenase of Escherichia coli have different metabolic origins

The Fe atom in the bimetallic active site of vertical bar NiFe vertical bar-hydrogenases has one CO and two cyanide ligands. To determine their metabolic origin, vertical bar NiFe vertical bar-hydrogenase-2 was isolated from Escherichia coli grown in the presence of L-vertical bar ureido-C-13 vertical bar citruiline, purified and analyzed bay infrared spectroscopy. The spectra indicate incorporation of C-13 only into the cyanide ligands and not into the CO, showing that cyanide and CO have different metabolic origins. After growth of E. coli in the presence of (CO)-C-13 only the CO ligand was labelled with 13C. Labelling did not result from an exchange of the intrinsic CO ligand with the exogenous CO. (C) 2007 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.