Understanding and Harnessing Hydrogenases, Biological Dihydrogen Catalysts - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 103

Figure 2 The enzymatic origin of microbial intracellular H 2 cycling within Escherichia coli ,a
bacterium capable of producing two membrane-bound dihydrogen uptake hydrogenases which
extend into the periplasm (hydrogenase-1 and hydrogenase-2) and one dihydrogen-producing
enzyme which extends into the cytoplasm. While hydrogenase-1 and -2 are 'wired' to the quinone
pool, hydrogenase-3 is part of a larger formate hydrogenlyase complex. Adapted from [ 62 ].