INVOLVEMENT OF HISTIDINE-RESIDUES IN THE CATALYTIC MECHANISM OF HYDROGENASES

In spite of their structural and amino acid sequence differences, Fe-o nly and Ni-containing hydrogenases achieved the same catalytic reactio ns. A chemical modification of histidine residues using a highly speci fic reagent (pentaammineruthenium II) has been carried out on Desulfov ibrio vulgaris Hildenborough Fe-hydrogenase and Desulfovibrio desulfur icans Norway Ni-Fe-Se-hydrogenase. The preliminary results obtained su ggest the existence of a general mechanism involving histidine residue s 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 D esulfovibrio vulgaris Hildenborough Fe-hydrogenase. (C) 1994 Academic Press, Inc.