Involvement of histidine residues in the catalytic mechanism of hydrogenases.

In spite of their structural and amino acid sequence differences, Fe-only and Ni-containing hydrogenases achieved the same catalytic reactions. A chemical modification of histidine residues using a highly specific reagent (pentaammineruthenium II) has been carried out on Desulfovibrio vulgaris Hildenborough Fe-hydrogenase and Desulfovibrio desulfuricans Norway Ni-Fe-Se-hydrogenase. The preliminary results obtained suggest the existence of a general mechanism involving histidine residues in the two groups of hydrogenases. These residues may be part of the histidine-containing motive shown to be present in both Fe- and Ni-Fe-hydrogenase sequences by Hydrophobic Cluster Analysis. This analysis also allows us to suggest a functional role for the small subunit of Desulfovibrio vulgaris Hildenborough Fe-hydrogenase.