The roles of hydrogenases 3 and 4, and the F 0F 1-ATPase, in H 2 production by Escherichia coli at alkaline and acidic pH

Abstract

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 CO 2 and H 2 during fermentative growth at low pH. Recently, an operon ( hyf) encoding a potential second H 2-evolving hydrogenase (Hyd-4) 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 Hyd-4, Fdh-H and F 0F 1-ATPase-dependent, and Fdh-H activity was partially dependent on Hyd-4 and F 0F 1-ATPase. These results suggest that, at slightly alkaline pH, H 2 production and Fdh-H activity are dependent on both the F 0F 1-ATPase and a novel FHL, designated FHL-2, which is composed of Hyd-4 and Fdh-H, and is driven by a proton gradient established by the F 0F 1-ATPase.