RELATIONSHIP BETWEEN HYDROGENASE AND NITROGENASE IN HYDROGEN METABOLISM OF PHOTOSYNTHETIC BACTERIUM RHODOPSEUDOMONAS CAPSULATA

The cells from cultures during photoheterotrophic growth with malate and glutamate ascarbon and nitrogen sources evolve substantial amounts of H_2, the evolution being mediatedby nitrogenase. This process is found to be totally dependent on light and electron donorsand is sensitive to ammonia. The cells from photoheterotrophic cultures possess an activehydrogenase too. The enzyme is particulate and bound to meinbranes, and catalyzes H_2uptake by various physiologically active substances, such as NADP, KNO_3, fumarate, methy-lene blue, benzyl viologen, etc. in the dark as electron acceptors. This process is markedlystimulated by ammonia. The photosynthetic nitrogenase activity, supported by H_2, showsmarkedly lowered sensitivity towards oxygen and is more efficient at low malate concentration.It will no longer be supported by H_2, when malate concentration becomes excessively high.The hydrogenase activity is irreversibly inhibited by acetylene. More hydrogen is evolved bynitrogenase after the inhibition of the hydrogenase activity. The physiological significanceof the interaction between hydrogenase and nitrogenase and its importance in the transitionbetween photoheterotrophic and photoautotrophic modes of growth are discussed.