Purification and characterization of serine-glyoxylate aminotransferase from kidney bean ( Phaseolus vulgaris)

Abstract

1. 1. Homogenates of kidney bean leaves were shown to catalyse aminotransferase reactions between the following compounds; serine:glyoxylate, alanine:glyoxylate, glutamic acid:glyoxylate and serine:pyruvate. A 100-fold purification of serine:glyoxylate aminotransferase yielded a preparation essentially free of alanine:glyoxylate aminotransferase and glutamate:glyoxylate aminotransferase; however, there was co-purification of serine:pyruvate aminotransferase. 2. 2. For serine:glyoxylate aminotransferase and serine:pyruvate aminotransferase double-reciprocal plots of the velocity of the reaction against one variable substrate at a series of fixed concentrations of the second substrate yielded sets of parallel lines and indicated a ping-pong reaction mechanism. The K M for glyoxylate and serine in the serine:glyoxylate aminotransferase reaction were 6·10 −4 M and 7.1·10 −4 M, respectively; and for pyruvate and serine in the serine:pyruvate aminotransferase reaction were 3.8·10 −2 M and 3.9·10 −4 M, respectively. 3. 3. Serine:glyoxylate aminotransferase and serine:pyruvate aminotransferase activities were inhibited by low concentrations of hydroxylamine but were less sensitive to N-ethylmaleimide and p-chloromercuribenzoate. Serine:glyoxylate aminotransferase activity was specifically inhibited by NH 4 −, the inhibition was linear competitive with serine and non-linear non-competitive with glyoxylate, the mechanism of HN 4 + inhibition is discussed. In contrast, serine:pyruvate amino-transferase activity was not inhibited by NH 4 +.