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¿ omitted¿000) pointed out that this cytochrome is reduced faster in the presence of catalytic amounts of tetraheme cytochrome c(3) (M(r) 13¿ omitted¿000) isolated from the same organism. The activation of the hydrogenase-dependent reduction of polyheme cytochromes by cytochrome c(3) (M(r) 13¿ omitted¿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¿ omitted¿000) would act as an electron shuttle in between hydrogenase and the polyheme cytochromes and its conductivity appears to be an important factor.