type	Journal Article
authors	Yagi, T.; Misono, H.; Tanizawa, K.; Yoshimura, T.; Soda, K.
title	Characterization of the half and overall reactions catalyzed by L- lysine:2-oxoglutarate 6-aminotransferase
journal	J Biochem (Tokyo)
Activity	2.6.1.36
ui	91201288
year	(1991)
volume	109
number	1
pages	61-5.
keywords	Binding Sites
abstract	Significant differences were found in the reaction rate, and the substrate and reaction specificities between the half reactions and the overall reactions catalyzed by L-lysine: 2-oxoglutarate 6- aminotransferase. The half reactions between an amino donor and the enzyme-bound pyridoxal 5'-phosphate, and also between an amino acceptor and the bound pyridoxamine 5'-phosphate followed first order reaction kinetics. The extrapolated first order rate constants and dissociation constants of the substrates were determined for the half reactions: lysine, 0.87 min-1 and 5.5 mM; glutamate, 1.1 min-1 and 10.5 mM; alanine, 0.66 min-1 and 6.6 mM; 6-aminohexanoate, 0.43 min-1 and 13.3 mM; and 2-oxoglutarate, 0.33 min-1 and 2.5 mM. As compared with the values reported for the overall reactions [Soda, K., Misono, H., & Yamamoto, T. (1968) Biochemistry 7, 4102-4109], the reactivity of the inherent substrates was lower by over 4 orders in the half reaction than that in the overall reaction, and the reactivity of alanine with the bound pyridoxal 5'-phosphate was reduced to 10% of that in the overall reaction. The substrate specificity in the half reaction was much lower than that in the overall reaction, which was re-examined in a reaction system containing the same concentration of the enzyme as that for the half reactions. Lysine 6-aminotransferase catalyzes the transfer of only the terminal amino group of lysine to 2-oxoglutarate in the overall reaction. However, in the half reaction, the 2-amino group as well as the terminal one was transferred to the bound pyridoxal 5'-phosphate. The ratio of reactivity of the 2-amino group to that of the 6-amino group was considerably influenced by the pH of the reaction mixture.(ABSTRACT TRUNCATED AT 250 WORDS)
last changed	2002/11/12 16:17