ELECTRON-TRANSFER BETWEEN HYDROGENASES AND MONOHEME AND MULTIHEME CYTOCHROMES IN DESULFOVIBRIO SSP

A comparative study of electron transfer between the 16 heme high mole cular mass cytochrome (Hmc) from Kesulfovibrio vulgaris Hildenborough and the [Fe] and [NiFe] hydrogenases from the same organism was carrie d out, both in the presence and in the absence of catalytic amounts of cytochrome Cg. For comparison, this study was repeated with the [NiFe ] hydrogenase from D. gigas. Hmc is very slowly reduced by the [Fe] hy drogenase, but faster by either of the two [NiFe] hydrogenases. In the presence of cytochrome c(3), in equimolar amounts to the hydrogenases , the rates of electron transfer are significantly increased and are s imilar for the three hydrogenases. The results obtained indicate that the reduction of Hmc by the [Fe] or [NiFe] hydrogenases is most likely mediated by cytochrome c(3). A similar study with D. vulgaris Hildenb orough cytochrome C-553 shows that, in contrast, this cytochrome is re duced faster by the [Fe] hydrogenase than by the [NiFe] hydrogenases. However, although catalytic amounts of cytochrome c3 have no effect in the reduction by the [Fe] hydrogenase, it significantly increases the rate of reduction by the [NiFe] hydrogenases.