Purification and Characterization of L-Alanine : 4,5-Dioxovalerate (Glyoxylate) Aminotransferase from Radish (Raphanus sativus L.) Seedlings

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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 1 5 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 local-ization of the enzyme and the lack of borrelation between the activity of this enzyme and chlorophyll synthesis, indicate that DOVA aminotransferase in radish is not involved in 5-aminolevulinate synthesis.
日本植物生理学会の論文