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Munoz-Munoz J.L.,GENZ Grupo de Investigacion Enzimologia | Garcia-Molina M.D.M.,GENZ Grupo de Investigacion Enzimologia | Garcia-Molina F.,GENZ Grupo de Investigacion Enzimologia | Berna J.,University of Murcia | And 4 more authors.
Journal of Molecular Catalysis B: Enzymatic | Year: 2013

A study of the diphenolase, o-aminophenol oxidase, and the aromatic o-diamine oxidase activities of tyrosinase carried out by measuring the catalysis and suicide inactivation kinetics provides the following information: catalytic constant, kcatS, Michaelis constant, KMS, the maximum apparent inactivation constant, λmaxS, and the partition ratio "r" between the suicide inactivation pathway and catalytic pathway or the number of turnovers made by one mol of enzyme before its inactivation. Analysis of these data, taking into account chemical shifts of the carbon atom supporting the hydroxyl or amino group, (δ) and σp+, enables a mechanism to be proposed for the transformation of o-diphenols, o-aminophenols and o-phenylendiamines into their products (o-quinones, o-quinoneimine and o-diimine), and, at the same time, for the suicide inactivation. The reaction constants in the representations of log kcatX/kcatH vs. σp+ according to Hammett's equation for the three types of substrate (o-diphenols, o-aminophenols and o-phenylendiamines) confirm that the catalysis mechanism is similar (simultaneous oxidation/reduction process on the two copper atoms). The dependence of log λmaxX/λmaxH vs. σp+ for the three substrate types reflects a lower reaction constant (in absolute value), which might indicate a similar reaction mechanism for the different molecules, but different from the previous mechanism, in that the oxidation/reduction only involves one copper atom. We also discuss the proposed mechanism and compare it with those described by other authors. Knowledge and quantification of the catalysis/inactivation process of tyrosinase might be of interest for optimizing applications such as wastewater treatment. © 2013 Elsevier B.V.


Munoz-Munoz J.L.,GENZ Grupo de Investigacion Enzimologia | Acosta-Motos J.R.,GENZ Grupo de Investigacion Enzimologia | Garcia-Molina F.,GENZ Grupo de Investigacion Enzimologia | Varon R.,University of Castilla - La Mancha | And 4 more authors.
Biochimica et Biophysica Acta - Proteins and Proteomics | Year: 2010

Under aerobic or anaerobic conditions, tyrosinase undergoes a process of irreversible inactivation induced by its physiological substrate l-dopa. Under aerobic conditions, this inactivation occurs through a process of suicide inactivation involving the form oxy-tyrosinase. Under anaerobic conditions, both the met- and deoxy-tyrosinase forms undergo irreversible inactivation. Suicide inactivation in aerobic conditions is slower than the irreversible inactivation under anaerobic conditions. The enzyme has less affinity for the isomer d-dopa than for l-dopa but the velocity of inactivation is the same. We propose mechanisms to explain these processes. © 2010 Elsevier B.V. All rights reserved.

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