The roles of hydrogenases 3 and 4, and the F0F1-ATPase, in H2 production by Escherichia coli at alkaline and acidic pH

The hyc operon of Escherichia coli encodes the H-2-evolving hydrogenase 3 (Hyd-3) complex that, in conjunction with formate dehydrogenase H (Fdh-H), constitutes a membrane-associated formate hydrogenlyase (FHL) catalyzing the disproportionation of formate to CO2 and H-2 during fermentative growth at low pH. Recently, an operon (hyf) encoding a potential second H-2-evolving hydrogenase (Hyd4) was identified in E. coli. In this study the roles of the hyc- and hyf-encoded systems in formate-dependent H-2 production and Fdh-H activity have been investigated. In cells grown on glucose under fermentative conditions at slightly acidic pH the production of H-2 was mostly Hyd-3- and Fdh-H-dependent, and Fdh-H activity was also mainly Hyd-3-dependent. However, at slightly alkaline pH, H-2, production was found to be largely Hyd4, Fdh-H and F0F1-ATPase-dependent, and Fdh-H activity was partially dependent on Hyd-4 and F0F1-ATPase. These results suggest that, at slightly alkaline pH, H-2 production and Fdh-H activity are dependent on both the F0F1-ATPase and a novel FHL, designated FHL-2, which is composed of Hyd-4 and Fdh-H, and is driven by a proton gradient establisbed by the F0F1-ATPase. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.