title: Kinetic study on the slow inhibition of epidermis tyrosinase by m-coumaric acid.
abstract: The inhibition by m-coumaric acid of oxidation of L-dopa by epidermis tyrosinase (monophenol,dihydroxy-L-phenylalanine:oxygen oxidoreductase, EC 1.14.18.1) is characterized by a prolonged transient phase. Kinetic data correspond to that for a postulated mechanism that involves rapid formation of a reduced enzyme-m-coumaric acid complex that subsequently undergoes a relatively slow reversible reaction. An overall inhibition constant for m-coumaric acid of 0.05 mM was calculated. The value of the Ki for the dissociation of m-coumaric acid from the rapidly formed complex was calculated as 0.53 mM. The first-order rate constants for the slow isomerization of the enzyme-inhibitor complex were calculated as 3.0 +/- 0.1 min-1 for the forward step and 0.31 +/- 0.06 min-1 for the reverse step.
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000037:antagonists & inhibitors*; D002934:Cinnamates / Q000494:pharmacology*; D003373:Coumaric Acids / Q000494:pharmacology*; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors*; D011893:Rana esculenta; D011895:Rana ridibunda; D012867:Skin / Q000201:enzymology*
chemical_list: D002934:Cinnamates; D003373:Coumaric Acids; C043332:3-coumaric acid; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase