FIG 10.

Vht of M. barkeri. The large hydrogenase subunit (VhtA) is located on the outside face of the cytoplasmic membrane and contains the bimetallic [NiFe] active site where H₂ is oxidized. This reaction generates 2 external H⁺ ions that contribute to proton motive force (shown in red) and 2 electrons that are transported via Fe-S clusters ([4Fe4S] and [3Fe4S]) located in the small subunit (VhtG) to heme b groups in the membrane-bound cytochrome b subunit (VhtC). Reduction of the electron carrier MP by VhtC involves uptake of 2 H⁺ ions from the cytoplasm, which are released externally upon MP oxidation (not shown). Brown lines trace the putative pathway of electron transport.