A sequential electron transfer from hydrogenases to cytochromes in sulfate-reducing bacteria

A central step in the energy metabolism of sulfate-reducing bacteria is the oxidation of molecular hydrogen, catalyzed by a periplasmic hydrogenase. The resulting electrons are then transferred to various electron transport chains and used for cytoplasmic sulfate reduction. The complex formation between [NiFeSe] hydrogenase and the soluble periplasmic polyheme cytochromes from Desulfomicrobium norvegicum was characterized by cross-linking experiments, BIAcore and kinetics analysis. Analysis of electron transfer between [NiFeSe] hydrogenase and octaheme cytochrome c(3) (M-r 26 000) pointed out that this cytochrome is reduced faster in the presence of catalytic amounts of tetraheme cytochrome c(3) (M-r 13 000) isolated from the same organism. The activation of the hydrogenase-dependent reduction of polyheme cytochromes by cytochrome c(3) (M-r 13 000), which is now described in both Desulfovibrio and Desulfomicrobium, is proposed as a general mechanism. During this process, cytochrome c(3) (M-r 13 000) would act as an electron shuttle in between hydrogenase and the polyheme cytochromes and its conductivity appears to be an important factor. (C) 2000 Elsevier Science B.V. All rights reserved.