Amino acid metabolism in plants. IV. Kinetic studies with a multispecific aminotransferase purified from bushbean seedlings (Phaseolus vulgaris L.).

Abstract

Kinetic studies were carried out on a purified multispecific aminotransferase isolated from bushbean roots. The enzyme was found to catalyze the transamination of L-aspartic and L-glutamic acids, as well as L-phenylalanine, L-tyrosine, and L-tryptophan when α-ketoglutarate or oxaloacetate was provided as the amino group acceptor. The Km values for these substrates and for the substrates of the reverse reactions were determined. Double-reciprocal plots of the data obtained for the initial relative velocities of the different aminotransferase activities indicate that all the transamination reactions catalyzed by this enzyme proceed through a binary complex mechanism. The evidence from competitive inhibition of the aromatic aminotransferase activity by the aliphatic substrate, L-aspartic acid, confirmed the view that only one enzyme is responsible for catalyzing the transamination reactions observed with this purified protein.