Isolation and characterization of an L-alanine: glyoxylate aminotransferase from human liver.

L-Alanine:glyoxylate aminotransferase was isolated from human liver and purified 900-fold. Pyridoxal phosphate was required for catalytic activity and enhanced the stability of the enzyme during purification and storage. The enzyme underwent activation when heated for 10 min in 10 PM pyridoxal phosphate. Activation resulted in the formation of a nondialyzable pyridoxal phosphate complex with the enzyme. The enzyme catalyzed the transfer of the CY-amino group of L-alanine to glyoxylate, forming glycine. This reaction was completely irreversible under all experimental conditions used. Serine, arginine, tryptophan, and hydroxypyruvate were less effective substrates. The Michaelis constants for alanine and pyridoxal phosphate were 1 x 1O-3 M and 1 X 10M6 M, respectively. The constant for glyoxylate could not be determined. The contribution of the enzyme to glycine, glyoxylate, and oxalate metabolism is considered, and the possible involvement of this enzyme in primary hyperoxaluria or oxalosis is discussed.