Inhibition Kinetics of Acetic Anhydride on Enzyme Activity of β-N-Acetyl-D-glucosaminidase from Pacific White Shrimp ( Penaeus vannamei ) / 中国生物化学与分子生物学报

ABSTRACT

β- N-Acetyl- D-glucosaminidase ( NAGase, EC3.2.1.52) is a composition of the chitinases and cooperates with endo-chitinase and exo-chitinase to disintegrate chitin into N-acetylglucosamine. Pacific White Shrimp (P. vannamei) NAGase is involved in digestion and molting processes. Some pollutants in seawater affect the enzyme activity causing loss of the biological function of the enzyme, which affects the exuviating shell and threatens the survival of the animal. The effects of acetic anhydride on the enzyme activity for the hydrolysis of pNP-NAG have been studied. The results show that acetic anhydride can lead to reversible non-competitive inhibition at appropriate concentrations, and the IC50 is estimated to be 9.0 mmol/L. The equilibrium constants have been determined for acetic anhydride binding with the enzyme and/or the enzymesubstrate complexes. Inhibition kinetics of acetic anhydride on the enzyme has been studied using the kinetic method of the substrate reaction. The results suggest that at pH 6.2, the action of acetic anhydride on the enzyme is first quick equilibrium binding and then slow inhibition. The microscopic rate constants have been determined for inhibition and reactivation. The results show that k + 0 is much larger than k - 0, indicating the enzyme is completely inactivated at sufficiently large modificator concentration.