THE PRESENT STATUS OF HYDROGEN RECYCLING IN LEGUMES

ABSTRACT A brief discussion is presented of recent information concerning (a) factors influencing extent of N2, loss during N2 fixation by legumes; (b) electron carriers involved in the oxyhydrogen reaction of Rhizobium japonicum bacteroids; and (c) progress made in evaluating H2 recycling advantages. A major factor determining whether H2 is evolved from legume nodules is the presence of an active uptake hydrogenase which participates in the oxidation of H2 that is evolved as a by-product of the nitrogenase reaction. The extent of H2 evolution from the nitrogenase reaction is affected by those factors that influence the nitrogenase turnover rate. These include the supply of ATP and reductant and the ratio of the Fe protein to the MoFe protein component of nitrogenase. Oxidation of H2 in Rhizobium bacteroids is catalyzed by a series of enzymes located in bacteroid membranes. In addition to the hydrogenase per se, carriers so far shown to be involved in the process include cytochromes of the b and c types a...