Kidney alanine: Glyoxylate aminotransferase isoenzymes; species distribution, subcellular distribution and properties

1. 1. The distribution of l-alanine:glyoxylate aminotransferase in the subcellular fractions of kidney was investigated with different mammalian species. In homogenates, the activity was relatively high in pig, rat, monkey, dog and cat, and low in mouse. Little or no activity was detected with human kidney. Most of the activity was present both in the mitochondria and in the soluble fraction in pig, rat, monkey, dog and cat. 2. 2. Mitochondrial extracts contained two forms of alanine: glyoxylate aminotransferase in dog and cat: one, designated isoenzyme 1, had a molecular weight of approx 80,000 and predominated in both species; the other, designated isoenzyme 2, had a molecular weight of approx. 175,000. In contrast, only isoenzyme 2 was contained in rat, pig and monkey kidney mitochondria. 3. 3. Isoenzyme 1 was purified from kidney mitochondrial extracts of dog and cat, and isoenzyme 2 from those of rat, pig and monkey. The two isoenzyme 1 preparations were specific for l-alanine and l-serine with glyoxylate as amino acceptor. Evidence that these two isoenzymes 1 are identical with l-serine:pyruvate aminotransferase was obtained. All three isoenzyme 2 preparations were specific for l-alanine and glyoxylate. 4. 4. Some other properties of isoenzymes 1 and 2 are described.