3.D.9 The H+-translocating F420H2 Dehydrogenase (F420H2DH) Family
A single F420H2 dehydrogenase (also referred to as F420H2: quinol oxidoreductase) from the methanogenic archaeon, Methanosarcina mazei Gö1, has been shown to be a redox driven proton pump. Reduction of 2-hydroxyphenazine by F420H2DH is accompanied by the translocation of 1 H+ per 2 electrons transferred. The gene cluster encoding the F420H2DH includes 12 genes, fpoABCDHIJKLMNO. Several of the subunits are related to those of the mitochondrial "complex I" NDH family members (TC#3.D.1). Thus, the gene products, FpoA, H, J, K, L, M and N, are highly hydrophobic and are homologous to subunits that form the membrane integral module of NDH-1. FpoB, C, D and I have their counterparts in the amphipathic membrane-associated module of NDH-1. However, homologues of the hydrophilic NADH-oxidizing input are absent. Instead, FpoF probably catalyzes F420H2 oxidation, providing the input module for transferring electrons to the membrane module, while one or more subunits (the output module) may be adapted to the reduction of methanophenazine.
The F420H2DH of M. mazei has a molecular size of about 120 kDa and contains Fe-S clusters and FAD. A similar 5 subunit enzyme has been isolated from Methanolobus tindarius. The sulfate-reducing Archaeoglobus fulgidus (and several other archaea) also have this enzyme.
The overall vectorial reaction catalyzed by F420H2DH is:
Reduced donor (2e-) + 1H+ (in) oxidized acceptor (2e-) + 1H+ (out).