Component of the F(420)H(2) dehydrogenase (FPO complex) which is part of the energy-conserving F(420)H(2):heterodisulfide oxidoreductase system. The membrane-bound electron transfer system of the complex plays an important role in the metabolism of methylotrophic methanogens when the organisms grow on methanol or methylamines. Catalyzes the oxidation of methanophenazine to dihydromethanophenazine. It shuttles electrons from F(420)H(2), via FAD and iron-sulfur (Fe-S) centers, to methanophenazine (an electron carrier in the membrane). It couples the redox reaction to proton translocation (for every two electrons transferred, two hydrogen ions are translocated across the cytoplasmic membrane), and thus conserves the redox energy in a proton gradient. It also catalyzes the oxidation of F(420)H(2) with quinones such as 2,3-dimethyl-1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone and tetramethyl-p-benzoquinone. H2 + methanophenazine = dihydromethanophenazine Measured for the whole complex. Optimum pH is 8.5. Optimum temperature is 39 degrees Celsius. FPO complex is composed of at least 13 different subunits. Belongs to the complex I subunit 1 family. Truncated N-terminus.