Acetate-Activating Enzymes of Bradyrhizobium japonicum Bacteroids

摘要

Acetyl coenzyme A (acetyl-CoA) synthetase and acetate kinase were localized within the soluble portion of Bradyrhizobium japonicum bacteroids, and no appreciable activity was found elsewhere in the nodule. The presence of each acetate-activating enzyme was confirmed by separation of the two enzyme activities on a hydroxylapatite column, by substrate dependence of each enzyme in both the forward and reverse directions, by substrate specificity, by inhibition patterns, and also by identification of the reaction products by C18 reverse-phase high-pressure liquid chromatography. Phosphotransacetylase activity, found in the soluble portion of the bacteroid, was dependent on the presence of potassium and was inhibited by added sodium. The greatest acetyl-CoA hydrolase activity was found in the root nodule cytosol, although appreciable activity also was found within the bacteroids. The combined specific activities of acetyl-CoA synthetase and acetate kinase-phosphotransacetylase were approximate to that of the pyruvate dehydrogenase complex, thus providing B. japonicum with sufficient capacity to generate acetyl-CoA.