FIGURE 2.

Diversity of the subunit architecture and cofactor content of electron bifurcating and confurcating hydrogenases. Enzymes of this class have been isolated and characterized from A. woodii (A), T. maritima (B), M. thermoacetica (C) and R. albus (D). All enzymes contain the subunits HydA, harboring the active site, the putative flavin-containing and NAD-binding subunit HydB, and the putative electron-transferring subunit HydC. A. woodii contains the additional subunit HydD. The arrangement of the iron–sulfur clusters and the binding site for ferredoxin are chosen arbitrary. Fd, ferredoxin.