Liver Cytosol Tyrosine Aminotransferase PRODUCT INHIBITION AND INTERACTION WITH SUBSTRATES

摘要: Abstract The reaction catalyzed by purified rat liver cytosol tyrosine aminotransferase (l-tyrosine + 2 oxoglutarate = p-hydroxyphenylpyruvate l-glutamate, EC 2.6.1.5) has been analyzed with regard to product inhibition and combination each of its rate-limiting substrates the Hill equation. Glutamate is a linear competitive inhibitor respect tyrosine, noncompetitive coenzyme or α-ketoglutarate. p-Hydroxyphenylpyruvate pyridoxal-P but These data, considered replots slopes intercepts, indicate "ping-pong" mechanism random in sense that either Schiff's base amino acid can add apoenzyme. A study half-reaction apoenzyme, pyridoxamine-P, α-ketoglutarate showed 90% more complete chemical rate was achieved when freshly isolated apoenzyme used. pH dependence paralleled supports conclusion same protein catalyzes half-reaction. Furthermore, magnitude compared transamination would dictate does not switch between ping-pong ordered depending upon level available. By use equation, enzyme first order pyridoxal-P, Reduction concentration value change pyridoxal-P. both these reactants levels varied affect Thus, homotropic effects are manifested this system.