Alanine aminotransferase and glycine aminotransferase from maize (Zea maysL.) leaves

Alanine aminotransferase (AlaAT, EC 2.6.1.2) and glycine aminotransferase ( GlyAT, EC 2.6.1.4), two different enzymes catalyzing transamination reactio ns with L-alanine as the amino-acid substrate, were examined in maize in wh ich alanine participates substantially in nitrogen transport. Preparative P AGE of a partially purified preparation of aminotransferases from maize lea ves gave 6 fractions differing in electrophoretic mobility. The fastest mig rating fraction I represents AlaAT specific for L-alanine as amino donor an d 2-oxoglutarate as amino acceptor. The remaining fractions showed three am inotransferase activities: L-alanine-2-oxoglutarate, L-alanine-glyoxylate a nd L-glutamate-glyoxylate. By means of molecular sieving on Zorbax SE-250 t wo groups of enzymes were distinguished in the PAGE fractions: of about 100 kDa and 50 kDa. Molecular mass of 104 kDa was ascribed to AlaAT in fractio n I, while the molecular mass of the three enzymatic activities in 3 fracti ons of the low electrophoretic mobility was about 50 kDa. The response of t hese fractions to: aminooxyacetate, 3-chloro-L-alanine and competing amino acids promted us to suggest that five out of the six preparative PAGE fract ions represented GIS AT isoforms, differing from each other by the L-glutam ate-glyoxylate:L-alanine-glyoxylate:L-alanine-2-oxoglutarate activity ratio .