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Hydrogenase activity and the H2 -fumarate electron transport system in a carbohydrate-fermenting obligate anaerobe,Bacteroides fragilis , were investigated. In both whole cells and cell extracts, hydrogenase activity was demonstrated with methylene blue, benzyl viologen, flavin mononucleotide, or flavin adenine dinucleotide as the electron acceptor. A catalytic quantity of benzyl viologen or ferredoxin fromClostridium pasteurianum was required to reduce nicotinamide adenine dinucleotide or nicotinamide adenine dinucleotide phosphate with H2 . Much of the hydrogenase activity appeared to be associated with the soluble fraction of the cell. Fumarate reduction to succinate by H2 was demonstrable in cell extracts only in the presence of a catalytic quantity of benzyl viologen, flavin mononucleotide, flavin adenine dinucleotide, or ferredoxin fromC. pasteurianum . Sulfhydryl compounds were not required for fumarate reduction by H2 , but mercaptoethanol and dithiothreitol appeared to stimulate this activity by 59 and 61%, respectively. Inhibition of fumarate reduction by acriflavin, rotenone, 2-heptyl-4-hydroxyquinoline-N -oxide, and antimycin A suggest the involvement of a flavoprotein, a quinone, and cytochromeb in the reduction of fumarate to succinate. The involvement of a quinone in fumarate reduction is also apparent from the inhibition of fumarate reduction by H2 when cell extracts were irradiated with ultraviolet light. Based on the evidence obtained, a possible scheme for the flow of electrons from H2 to fumarate inB. fragilis is proposed.

Hydrogenase Activity and the H 2 -Fumarate Electron Transport System in Bacteroides fragilis

Hydrogenase Activity and the H ₂ -Fumarate Electron Transport System in Bacteroides fragilis