Purification, characterization and identification of tryptophan aminotransferase from rat brain

Tryptophan aminotransferase was purified from rat brain extracts. The purified enzyme had an isoelectric point at pH 6.2 and a pH optimum near 8.0. On electrophoresis the enzyme migrated to the anode. The enzyme was active with oxaloacetate or 2-oxoglutarate as amino acceptor but not with pyruvate, and utilized various L-amino acids as amino donors. With 2-oxoglutarate, the order of effectiveness of the L-amino acids was aspartate >> 5-hydroxytryptophan > tryptophan > tyrosine > phenylalanine. Aminotransferase activity of the enzyme towards tryptophan was inhibited by L-glutamate. Sucrose density gradient centrifugation gave a molecular weight of approx. 55,000. The enzyme was present in both the cytosol and synaptosomal cytosol, but not in the mitochondria. The isoelectric focusing profile of tryptophan: oxaloacetate aminotransferase activity was identical with that of L-aspartate: 2-oxoglutarate aminotransferase (EC 2.6.1.1) activity, with both subcellular fractions. On the basis of these data, it is suggested that the enzyme is identical with the cytosol aspartate: 2-oxoglutarate aminotransferase.