Activation Changes of Hafnia alvei Aspartase by Acetic Anhydride

Abstract

The Hafnia alvei aspartase activity with acetic anhydride treatment gradually increased and reached 7.5-fold that of the native one. The activity of the acetylated aspartase was a little higher than that of the native enzyme, indicating that the cooperativity between a substrate and enzyme is increased. The optimum temperature of the native aspartase was 45∘C, and that of the acetylated enzyme shifted to 40∘C. The pH vs. the activity profile of the acetylated aspartase was also different from that of the native enzyme. The initial velocity patterm of the acetylated aspartase intersects to the left of the ordinate, indicating the sequential kinetic mechanism other than a rapid equilibrium ordered one. The reciprocal plots for aspartate of the native aspartase wewe curved, but those of the acetylated aspartase wewe linear, indicating the Michaelis-Menten kinetics. The helical content of the acetylated aspartase was rather decreased to 9% than that (63%) of the native one,