HYDROGENASE AND HYDROGEN METABOLISM IN MICROCOCCUS AEROGENES

Abstract

M. aerogenes, an obligate anaerobe, produces H2 from pyruvate, certain amino acids, purines and pyrimidines, though not from sugars and formate. Tests for the enzyme hydrogenase by catalytic hydro-genations of methylene blue, fumarate, ferricyanide, nitrate and O2 were negative. M. aerogenes catalyzed the exchange reaction with deuterium and reduces methyl violet and benzyl viologen in the presence of H2. Hence, there is present an enzyme which has the classicalproperties of hydrogenase, i.e., is able to carry out enzymatic activation of H2 with the reduction of acceptor compounds. Methylene blue in the oxidized form inhibits not only the exchange reaction but also the reduction of methyl violet and benzyl viologen. This toxicity of methylene blue explains the failure to demonstrate hydrogenase activity in the conventional assay with methylene blue. In the presence of pyruvate, both H2 evolution and deuterium exchange are blocked by oxidized methylene blue. Once the methylene blue is reduced, active exchange and evolution of H2 from pyruvate occurs. Evidence indicates that hydrogenase is a necessary component of the enzyme complex responsible for evolution of H2 from pyruvate, as well as being involved in the exchange reaction and in the reduction of methyl violet and benzyl viologen.