title: Enzymatic characterization and functional groups of polyphenol oxidase from the pupae of blowfly (Sarcophaga bullata).
abstract: Polyphenol oxidase (EC 1.14.18.1) was purified from the pupae of blowfly (Sarcophaga bullata) by a procedure involving ammonium sulfate fractionation and chromatography on DEAE-cellulose and Sephadex G-100. Kinetic characteristics of the enzyme were determined using L-DOPA as substrate. The specific activity of the enzyme was 770 U/mg, and the Michaelis constant (Km) was 1.5 +/- 0.1 mM (pH 6.8, 30 degrees C). Activity was maximal at 40 degrees C, pH 6.5. Chemical modification experiments demonstrated that cysteine and tryptophan residues are essential and arginine residues are not essential to the enzyme function. The enzyme is inhibited by quercetin with an IC50 of 0.20 +/- 0.06 mM. The inhibition is of competitive type, and the inhibition constant was determined to be 88 micro M.
authors.affiliation: Key Laboratory of Ministry of Education for Cell Biology and Tumor Cell Engineering, School of Life Sciences, Xiamen University, Xiamen, 361005, China.
authors.forename: Qin
authors.initials: Q
authors.lastname: Wang
authors.forename: Qing-Xi
authors.initials: QX
authors.lastname: Chen
authors.forename: Xiao-Hong
authors.initials: XH
authors.lastname: Huang
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Ke
authors.forename: Yan
authors.initials: Y
authors.lastname: Shi
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D004175:Diptera / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D020128:Inhibitory Concentration 50; D007700:Kinetics; D011679:Pupa / Q000201:enzymology*; D011794:Quercetin / Q000494:pharmacology; D013329:Structure-Activity Relationship
chemical_list: D011794:Quercetin; D004156:Catechol Oxidase