The effect of pH on the suicide inactivation of frog epidermis tyrosinase.
This paper presents a new reaction mechanism for the effect of the pH on the suicide inactivation of the diphenolase activity of tyrosinase. The applicability of the mechanism is supported by the experimental characterization of the kinetic behaviour of the frog epidermis enzyme acting on catechol, L-dopa and alpha-methyldopa at several pH values. Two enzyme froms 'met-' and 'oxy-' tyrosinase, but no their corresponding enzyme-diphenol complexes, present one ionizable group with very similar value of Ka which has been determined. The highest values of catalytic and inactivation efficiencies correspond to alpha-methyldopa and catechol, respectively. These kinetic studies have been carried out by using the transient phase approach previously developed, with negligible substrate consumption during the assay time. That illustrate the usefulness of the method for multisubstrate enzyme reactions.
García Moreno
M
M
Departamento de Química-Física, E.U. Politécnica de Albacete, Universidad de Castilla-La Mancha, Spain.
Varón
R
R
Sánchez Gracia
A
A
Tudela
J
J
García Cánovas
F
F
D000818:Animals; D002396:Catechols / Q000378:metabolism / Q000494:pharmacology; D004795:Enzyme Stability; D004817:Epidermis / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007980:Levodopa / Q000378:metabolism / Q000494:pharmacology; D008750:Methyldopa / Q000378:metabolism / Q000494:pharmacology; D008954:Models, Biological; D014442:Monophenol Monooxygenase / Q000187:drug effects / Q000378:metabolism*; D011898:Ranidae
D002396:Catechols; D007980:Levodopa; D008750:Methyldopa; D014442:Monophenol Monooxygenase