Mechanistic implications of variable stoichiometries of oxygen consumption during tyrosinase catalyzed oxidation of monophenols and o-diphenols.
The stoichiometry of oxygen consumption during tyrosinase-catalyzed oxidation of an o-diphenol (4-tert-butylcatechol, TBC) and a monophenol (4-tert-butylphenol, TBP) has been determined. At high [substrate]/[enzyme] ratios, in the case of o-diphenols, the stoichiometry of the enzyme-catalyzed reaction was always 1 O(2)/2 o-diphenols, although if the o-quinone product was unstable, the apparent stoichiometry could tend to 1 O(2)/1 o-diphenol due to regeneration of an o-diphenol in a side reaction. In the case of monophenols, the stoichiometry could be 1 O(2)/1 monophenol or 1.5 O(2)/1 monophenol depending if the o-quinone product was stable or unstable, respectively. However, at low [substrate]/[enzyme] ratios, the oxygen/substrate stoichiometry could, even in the case where stable products are formed, be lower than 1 O(2)/2 substrates for o-diphenols or higher than 1 O(2)/1 substrate for monophenols. These data supported the mechanism proposed by Rodríguez-López et al. [J. Biol. Chem. 267 (1992) 3801-3810], in which, during hydroxylation of monophenols, tyrosinase first transformed monophenol to o-diphenol and then either catalyzed a further oxidation to form o-quinone or released it into the reaction medium. In this second case, subsequent oxidation of the o-diphenol resulted in additional oxygen consumption.
Peñalver
María José
MJ
GENZ: Grupo de Investigación de Enzimología, Departamento de Bioquímica y Biología Molecular-A, Facultad de Biología, Universidad de Murcia, A. Correos 4021, E-30080 Espinardo, Murcia, Spain.
Hiner
Alexander N P
AN
Rodríguez-López
José Neptuno
JN
García-Cánovas
Francisco
F
Tudela
José
J
D004156:Catechol Oxidase / Q000737:chemistry*; D002396:Catechols / Q000737:chemistry; D003198:Computer Simulation; D007700:Kinetics; D008956:Models, Chemical; D014442:Monophenol Monooxygenase / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry; D013379:Substrate Specificity
D002396:Catechols; D010636:Phenols; C015047:p-tert-butyl catechol; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; C006862:butylphen; D010100:Oxygen