title: Inhibitory kinetics of beta-N-acetyl-D-glucosaminidase from prawn (Litopenaeus vannamei) by zinc ion.
abstract: Prawn (Litopenaeus vannamei) beta-N-acetyl-D-glucosaminidase (NAGase, EC 3.2.1.52) is involved in the digestion and molting processes. Zinc is one of the most important metals often found in the pollutant. In this article, the effects of Zn(2+) on prawn NAGase activity for the hydrolysis of pNP-NAG have been investigated. The results showed that Zn(2+) could reversibly and noncompetitively inhibit the enzyme activity at appropriate concentrations and its IC(50) value was estimated to be 6.00 +/- 0.25 mM. The inhibition model was set up, and the inhibition kinetics of the enzyme by Zn(2+) has been studied using the kinetic method of the substrate reaction. The inhibition constant was determined to be 11.96 mM and the microscopic rate constants were also determined for inactivation and reactivation. The rate constant of the inactivation (k(+0)) is much larger than that of the reactivation (k(-0)). Therefore, when the Zn(2+) concentration is sufficiently large, the enzyme is completely inactivated. On increasing the concentration of Zn(2+), the fluorescence emission peak and the UV absorbance peak are not position shifted, but the intensity decreased, indicating that the conformation of Zn(2+)-bound inactive NAGase is stable and different from that of native NAGase. We presumed that Zn(2+) made changes in the activity and conformation of prawn NAGase by binding with the histidine or cysteine residues of the enzyme.
authors.affiliation: Key Laboratory of Ministry of Education for Cell Biology and Tumor Cell Engineering, School of Life Sciences, Xiamen University, Xiamen, China.
authors.forename: Xiao-Lan
authors.initials: XL
authors.lastname: Xie
authors.forename: Qian-Sheng
authors.initials: QS
authors.lastname: Huang
authors.forename: Min
authors.initials: M
authors.lastname: Gong
authors.forename: Juan
authors.initials: J
authors.lastname: Du
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Qing-Xi
authors.initials: QX
authors.lastname: Chen
mesh_terms: D000118:Acetylglucosaminidase / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D000818:Animals; D001665:Binding Sites; D002412:Cations / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006868:Hydrolysis; D020128:Inhibitory Concentration 50; D007700:Kinetics; D033561:Penaeidae / Q000201:enzymology*; D011487:Protein Conformation / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013379:Substrate Specificity; D015032:Zinc / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D002412:Cations; D000118:Acetylglucosaminidase; D015032:Zinc