Enzymic Characterization of Leaf Peroxisomes

Abstract

Abstract Peroxisomes from spinach leaves contain three aminotransferases, a glutamate-glyoxylate, a serine-pyruvate and an aspartate aminotransferase. Five other enzymes previously described in leaf peroxisomes were measured, namely, catalase, glycolate oxidase, NADH-hydroxypyruvate reductase, and NAD-malate dehydrogenase. A NADPisocitrate dehydrogenase was also associated with isolated leaf peroxisomes, but its specific activity was much less than the other enzyme. Most of the NADP-isocitrate dehydrogenase activity was soluble. Serine-pyruvate aminotransferase activity in the particulate fraction was localized entirely in the peroxisomes. Isoenzymes of asparate aminotransferase were found in chloroplasts, mitochondria, and peroxisomes. The activities of the chloroplast and mitochondrial forms of this aminotransferase were greater than the peroxisomal isoenzyme. The two peroxisomal serine-pyruvate and aspartate aminotransferases were separated by disc electrophoresis and isoelectric focusing. The aminotransferases had different substrate specificity. Other enzymes of the tricarboxylic acid cycle, with the exception of an isoenzyme of NAD-malate dehydrogenase, were detected in mitochondria but not in the leaf peroxisomal fractions. Enzymes for the reductive amination of α-keto acids, the interconversion of C4 and C3 acids, hydroxyaspartate dehydratase, and the α and β oxidation systems for fatty acids could not be detected in leaf peroxisomes. Preliminary evidence is presented for a malate synthase in leaf mitochondria.