Glutamate:glyoxylate aminotransferase from the seedlings of rye (Secale cereale L.)

Glutamate:glyoxylate aminotransferase from green parts of 7-day-old rye seedlings was purified almost to homogeneity. Specific activity of the purified enzyme measured with L-glutamate and glyoxylate as substrates, was 46.1 units/mg. The enzyme activity with L-alanine and 2-oxoglutarate as substrates was higher by a factor of 1.5, whereas with L-alanine and glyoxylate or L-glutamate and pyruvate it was similar to that with L-glutamate and glyoxylate. L-Aspartate, L-arginine and L-ornithine could also serve as substrate. The reaction followed the Ping-Pong Bi Bi mechanism and Km values for L-glutamate and glyoxylate were 2.6 and 0.5 mM, respectively. Pyridoxal phosphate was found to be the coenzyme of glutamate-glyoxylate aminotransferase. This coenzyme was rather tightly bound with the enzyme protein, as the attempts at its complete resolution from the apoenzyme were unsuccessful. Pyridoxal phosphate, 2-mercaptoethanol and sucrose, or bovine serum albumin stabilized the enzyme. Molecular weight of glutamate:glyoxylate aminotransferase from rye seedlings, determined by SDS-polyacrylamide gel electrophoresis, was 58,800 +/- 2,100, whereas molecular sieving on Sephacryl S-200 gel gave values of 70,800 +/- 700 or 61,400. Similar values obtained for the denatured and nondenatured enzyme seem to indicate that it is a monomeric protein.