title: Comparative study of tyrosinases from different sources: relationship between halide inhibition and the enzyme active site.
abstract: The inhibition of tyrosinases from frog epidermis (Rana esculenta ridibunda), mushroom (Agaricus bisporus) and Harding-Passey mouse melanoma by halides is compared. In all cases, the inhibition is pH dependent, increasing when the pH decreases. The order of inhibition is I- greater than Br- greater than Cl- much greater than F- for frog epidermis tyrosinase, F- greater than I- greater than Cl- greater than Br- for mushroom tyrosinase and F- greater than Cl- much greater than Br- greater than I- for the mouse melanoma enzyme. These results are discussed in terms of the active site accessibility to exogenous ligands. The activation energies of the enzyme-catalysed L-dopa oxidation were also calculated, being the values 6.86, 17.01 and 20.25 kcal/mol for frog epidermis, mushroom and Harding-Passey mouse melanoma, respectively. A relationship between these values and the evolutionary adaptation of these enzymes is proposed.
authors.forename: J H
authors.initials: JH
authors.lastname: Martinez
authors.forename: F
authors.initials: F
authors.lastname: Solano
authors.forename: R
authors.initials: R
authors.lastname: Peñafiel
authors.forename: J D
authors.initials: JD
authors.lastname: Galindo
authors.forename: J L
authors.initials: JL
authors.lastname: Iborra
authors.forename: J A
authors.initials: JA
authors.lastname: Lozano
mesh_terms: D000818:Animals; D001487:Basidiomycota / Q000201:enzymology*; D001965:Bromides / Q000494:pharmacology*; D004156:Catechol Oxidase / Q000037:antagonists & inhibitors*; D002712:Chlorides / Q000494:pharmacology*; D005459:Fluorides / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007454:Iodides / Q000494:pharmacology*; D007700:Kinetics; D008545:Melanoma / Q000201:enzymology*; D051379:Mice; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors*; D011893:Rana esculenta; D012867:Skin / Q000201:enzymology*; D013816:Thermodynamics
chemical_list: D001965:Bromides; D002712:Chlorides; D007454:Iodides; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; D005459:Fluorides