title: Inhibitory kinetics of citric acid on beta-N-acetyl-d-glucosaminidase from prawn (Litopenaeus vannamei).
abstract: NAGase (EC.3.2.1.52) from crustaceans has the important roles in immunity, molting and digestion of chitinous foods. In this paper, the effects of citric acid on the activity of NAGase from Litopenaeus vannamei for the hydrolysis of pNP-NAG have been studied. The results showed that appropriate concentrations of citric acid could lead to reversible inhibition on NAGase and IC(50) was estimated to be 5.00 +/- 0.35 mM. Using the plots of Lineweaver-Burk, the inhibition of NAGase by citric acid belongs to competitive type, the inhibitory equilibrium constant for citric acid binding with free NAGase, K(I), is 3.26 +/- 0.25 mM. The inhibitory kinetics of citric acid on NAGase in the appropriate concentrations of citric acid has been studied using the kinetic method of substrate reaction. The time course of NAGase for the hydrolysis of pNP-NAG in the presence of different concentrations of citric acid showed that at each citric acid concentration, the rate decreased with increasing time until a straight line was approached. The results show that the inhibition of NAGase by citric acid is a slow, reversible reaction with fractional remaining activity. The microscopic rate constants are determined for the reaction on citric acid with NAGase.
authors.affiliation: School of Chemistry and Life Sciences, Quanzhou Normal University, Quanzhou 362000, China.
authors.forename: Xiao-Lan
authors.initials: XL
authors.lastname: Xie
authors.forename: Yong-Hua
authors.initials: YH
authors.lastname: Hu
authors.forename: Ling-Ling
authors.initials: LL
authors.lastname: Wang
authors.forename: Chao-Qi
authors.initials: CQ
authors.lastname: Chen
authors.forename: Qian-Sheng
authors.initials: QS
authors.lastname: Huang
authors.forename: Han-Tao
authors.initials: HT
authors.lastname: Zhou
authors.forename: Qing-Xi
authors.initials: QX
authors.lastname: Chen
mesh_terms: D000818:Animals; D019343:Citric Acid / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D033561:Penaeidae / Q000201:enzymology*; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D019343:Citric Acid; D001619:beta-N-Acetylhexosaminidases