L-TRYPTOPHAN AND D-TRYPTOPHAN AMINOTRANSFERASES FROM MAIZE COLEOPTILES

Two forms of L-tryptophan aminotransferases (L-TAT-1 and L-TAT-2) and one D-tryptophan aminotransferase (D-TAT) were separated from maize coleoptiles by using L- and D-tryptophan as amino group donors. The enzymes were partially purified by hydrophobic and gel filtration column chromatographies. L-TAT-1 and L-TAT-2 had similar properties, showing optimum pH at 8-9 and a high optimum temperature of 50-60 C for catalytic activity. As the amino group acceptor for these two enzymes, alpha-keto glutaric acid was more effective than pyruvic, oxaloacetic and glyoxylic acids. The molecular masses of L-TAT-1 and L-TAT-2 estimated by gel filtration were approximately 80 kDa and 45 kDa, respectively. D-TAT had an optimum pH similar to those of L-TATs, but the optimum temperature was considerably lower (30 C). Pyruvic acid was an effective amino group acceptor for D-TAT, whereas oxaloacetic and alpha-keto glutaric acids were not. D-Cycloserine completely inhibited the activity. The molecular mass of D-TAT was approximately 55 kDa. These three TATs required pyridoxal-5-phosphate for their catalytic activities.