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Kinetic cooperativity of tyrosinase. A general mechanism

100%
Muñoz-Muñoz J. L., Garcia-Molina F., Varon R., Tudela J., Garcia-Cánovas F., Rodríguez-López J. N.
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2011
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vol. 58
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issue 3
303-311
EN
Tyrosinase shows kinetic cooperativity in its action on o-diphenols, but not when it acts on monophenols, confirming that the slow step is the hydroxylation of monophenols to o-diphenols. This model can be generalised to a wide range of substrates; for example, type SA substrates, which give rise to a stable product as the o-quinone evolves by means of a first or pseudo first order reaction (α-methyl dopa, dopa methyl ester, dopamine, 3,4-dihydroxyphenylpropionic acid, 3,4-dihydroxyphenylacetic acid, α-methyl-tyrosine, tyrosine methyl ester, tyramine, 4-hydroxyphenylpropionic acid and 4-hydroxyphenylacetic acid), type SB substrates, which include those whose o-quinone evolves with no clear stoichiometry (catechol, 4-methylcatechol, phenol and p-cresol) and, lastly, type SC substrates, which give rise to stable o-quinones (4-tert-butylcatechol/4-tert-butylphenol).
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Indirect inactivation of tyrosinase in its action on tyrosine

84%
Muñoz-Muñoz J. L., Garcia-Molina F., Acosta-Motos J. R., Arribas E., Garcia-Ruíz P. A., Tudela J., Garcia-Cánovas F., Rodríguez-López J. N.
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2011
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vol. 58
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issue 4
477-488
EN
Under aerobic conditions, tyrosinase is inactivated by dopa as a result of suicide inactivation, and, under anaerobic conditions, as a result of irreversible inactivation. However, tyrosine protects the enzyme from being inactivated by dopa under anaerobic conditions. This paper describes how under aerobic conditions the enzyme acting on tyrosine is not directly inactivated but undergoes a process of indirect suicide inactivation provoked by reaction with the o-diphenol originated from the evolution of o-dopaquinone and accumulated in the reaction medium.
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