title: Irreversible inhibitory kinetics of mercuric ion on N-acetyl-β-D-glucosaminidase from Nile tilapia (Oreochromis niloticus).
abstract: N-acetyl-β-D-glucosaminidase (EC 3.2.1.52, NAGase), hydrolyzes dimers or trimers of N-acetyl-β-D-glucosamine (NAG) into monomers and is shown to be important for the reproduction of male animals. NAGase is purified from the spermary of Nile tilapia, and its enzyme activity can be strongly inhibited by mercuric chloride (HgCl2). In this paper, we determined the kinetics of HgCl2-mediated inhibition of NAGase, and our results showed that it was irreversible inhibition with an IC50 value at 2.70±0.02 μM. Moreover, Hg(2+) reduced the thermal and pH stability of the enzyme. We determined the inhibition kinetics of Hg(2+) by using the kinetic method of substrate reaction. With this inhibition model, the microscopic rate constants for the reaction of Hg(2+) with free enzyme (k1) and the enzyme-substrate complex ( [Formula: see text] ) were determined to be 4.42×10(-4) mM(-1) s(-1) and 7.06×10(-5) mM(-1) s(-1), respectively, indicating that the presence of substrate can protect NAGase from Hg(2+) inhibition.
authors.affiliation: University Key Lab for Integrated Chinese Traditional and Western Veterinary Medicine and Animal Healthcare in Fujian Province, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
authors.forename: Wei-Ni
authors.initials: WN
authors.lastname: Zhang
authors.affiliation: School of Life Sciences, Xiamen University, Xiamen 361005, China.
authors.forename: Qing-Xi
authors.initials: QX
authors.lastname: Chen
authors.affiliation: University Key Lab for Integrated Chinese Traditional and Western Veterinary Medicine and Animal Healthcare in Fujian Province, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
authors.forename: Xin-Yu
authors.initials: XY
authors.lastname: Lin
authors.affiliation: University Key Lab for Integrated Chinese Traditional and Western Veterinary Medicine and Animal Healthcare in Fujian Province, Fujian Agriculture and Forestry University, Fuzhou 350002, China. Electronic address: xhhuang138@hotmail.com.
authors.forename: Xiao-Hong
authors.initials: XH
authors.lastname: Huang
authors.affiliation: University Key Lab for Integrated Chinese Traditional and Western Veterinary Medicine and Animal Healthcare in Fujian Province, Fujian Agriculture and Forestry University, Fuzhou 350002, China. Electronic address: zjhyfang138@yahoo.com.cn.
authors.forename: Yi-Fan
authors.initials: YF
authors.lastname: Huang
mesh_terms: D000118:Acetylglucosaminidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D023681:Cichlids / Q000502:physiology*; D004795:Enzyme Stability / Q000187:drug effects; D020128:Inhibitory Concentration 50; D007477:Ions / Q000633:toxicity; D007700:Kinetics; D008297:Male; D008627:Mercuric Chloride / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D007477:Ions; D014874:Water Pollutants, Chemical; D008627:Mercuric Chloride; D000118:Acetylglucosaminidase
keywords: Irreversible inhibitory kinetics; Mercuric ion; N-acetyl-β-d-glucosaminidase; Oreochromis niloticus