Biosynthesis of porphyrin precursors in mammals. Identity of alanine: gamma, delta-dioxovalerate aminotransferase with alanine:glyoxylate aminotransferase.

Alanine: gamma, delta-dioxovalerate aminotransferase had been purified from bovine liver mitochondria, and the capacity of this enzyme to form delta-aminolevulinic acid had been suggested to be far greater than that of delta-aminolevulinate synthase (EC 2.3.1.37) from the same mitochondria (Varticovski, L., Kushner, J. P., and Burnham, B. F. (1980) J. Biol. Chem. 255, 3742-3747). In the present study, alanine: gamma, delta-dioxovalerate aminotransferase and alanine-glyoxylate aminotransferase (EC 2.6.1.44) were co-purified to homogeneity from bovine liver mitochondria. The ratio of the two activities remains constant during purification and is unchanged by a variety of treatments of the purified enzyme. Alanine: gamma, delta-dioxovalerate aminotransferase activity is competitively inhibited by glyoxylate. Some kinetic data are presented. These results show that the two activities are associated with the same protein. The enzyme is much higher in the glyoxylate aminotransferase activity than in the dioxovalerate aminotransferase activity. The purified enzyme has a molecular weight of approximately 240,000 with four identical subunits and an isoelectric point of 5.4. The ratio of the gamma, delta-dioxovalerate aminotransferase activity to the glyoxylate aminotransferase was determined with alanine:glyoxylate aminotransferase preparations from various mammalian liver and kidney.