Organic Acid Metabolism in Cellular Organelles of Vigna cylindrica (Mitorisasage) Cotyledons

In starchy cotyledons of Vigna cylindrica (L.) Skeels (Mitorisasage) during seed germination, the enzymes of the glyoxylate cycle were located in the matrix of mitochondria. Glyoxysomes were absent. The glyoxylate cycle in the mitochondria supplies organic acids to the tricarboxylic acid cycle. In mitochondria, isocitrate lyase activity was much higher than malate synthase activity. Part of the glyoxylate thus produced in mitochondria may be nonenzymatically converted to formate by H2O2 and the formate then converted to CO2 by peroxidase or by formic dehydrogenase. The activity of superoxide dismutase, which supplies H2O2, was higher in mitochondria than in peroxisomes. The remaining glyoxylate in mitochondria is possibly converted to glycine by alanine-glyoxylate aminotransferase or transported to peroxisomes which lacked isocitrate lyase activity but had high malate synthase activity. In peroxisomes, glyoxylate may be also produced from urate, as is suggested by the fairly high activities of uricase, allantoinase and allantoicase. Judging from the enzyme distribution, Vigna peroxisomes should be capable of producing malate, oxalacetate, citrate, isocitrate and a-ketoglutarate.