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Deuterium isotope effect on the suicide inactivation of tyrosinase in its action on o‐ diphenols
Author(s) -
MuñozMuñoz Jose Luis,
del Mar GarcíaMolina María,
GarciaMolina Francisco,
GarciaRuiz Pedro Antonio,
GarciaSevilla Francisco,
RodriguezLopez Jose N.,
GarciaCanovas Francisco
Publication year - 2013
Publication title -
iubmb life
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.132
H-Index - 113
eISSN - 1521-6551
pISSN - 1521-6543
DOI - 10.1002/iub.1191
Subject(s) - kinetic isotope effect , deuterium , chemistry , tyrosinase , catechol , proton , medicinal chemistry , catechol oxidase , photochemistry , reaction rate constant , stereochemistry , kinetics , nuclear chemistry , enzyme , organic chemistry , polyphenol oxidase , peroxidase , physics , quantum mechanics
A solvent deuterium isotope effect on the inactivation suicide of tyrosinase in its action on o‐ diphenols (catechol, 4‐methylcatechol, and 4‐tert‐butylcatechol) was observed. This isotope effect, observed during kinetic studies in the transition phase, was higher than that described previously in the steady state, indicating that there is an additional slow step in the suicide inactivation mechanism, which we believe to be responsible for the inactivation. In a proton inventory study of oxidation of o‐ diphenols, the representation ofλ max D , f n/ λ max D , f 0versus n (atom fractions of deuterium), whereλ max D , f nis the maximum apparent inactivation constant for a molar fraction of deuterium ( n ) andλ max D , f 0is the corresponding kinetic parameter in a water solution, was linear for all substrates. This suggests that only one of the protons transferred from the two hydroxyl groups of the substrate, which are oxidized in one turnover, is responsible for the isotope effects. We propose that this proton could be the proton transferred from the hydroxyl group of C‐2 to the hydroperoxide of the oxytyrosinase form ( E ox ) and that it probably causes enzyme inactivation through the reduction of the Cu 2+ A to Cu 0 and its subsequent release from the active site. © 2013 IUBMB Life, 65(9):793–799,2013