Studies on hydrogen oxidation in cell-free extracts of Hydrogenomonas eutropha

Hydrogen oxidation has been studied in cell-free extracts of autotrophically grown Hydrogenomonas eutropha. In crude extracts diphosphopyridine nucleotide, oxygen and a variety of dyes can serve as electron acceptors during hydrogen oxidation. The reduction of diphosphopyridine nucleotide by hydrogen appears to require the mediation of one or more unidentified cofactors. Hydrogenase, as assayed either by methylene blue reduction or by diphosphopyridine nucleotide reduction, is recovered in the supernatant fluid after centrifugation for 1 h at 144,000 × g. These “soluble” hydrogenase preparations contain endogenous flavin and a single cytochrome of the “ c” type, both of which are reduced by hydrogen and by reduced diphosphopyridine nucleotide. The extracts also catalyse an aerobic oxidation of reduced diphosphorydine nucleotide via a cyanide sensitive pathway.