Purification and characterization of l-alanine: 4,5-dioxovalerate (glyoxylate) aminotransferase from radish (raphanus sativus l.) seedlings

L-Alanine:4,5-dioxovalerate (DOVA) aminotransferase was purified 131-fold and characterized from greening seedlings of radish (Raphanus sativus L.). The enzyme was shown to be identical with alanine:glyoxylate aminotransferase. The rate of activity of DOVA aminotransferase was 15 times less than that of glyoxylate aminotransferase. Its molecular weight was estimated to be approximately 123,000 with two identical subunits, and exhibited a single, broad pH optimum at 8.0. DOVA aminotransferase activity was competitively inhibited by glyoxylate. A kinetic study of the enzyme at different alanine concentrations suggested a ping pong reaction mechanism. The K_m values for DOVA and L-alanine were 0.71 and 1.7 mM, respectively.The activity ratio of transamination under various conditions, the cellular localization of the enzyme and the lack of correlation between the activity of this enzyme and chlorophyll synthesis, indicate that DOVA aminotransferase in radish is not involved in 5-aminolevulinate synthesis.