Kinetic cooperativity of tyrosinase. A general mechanism |
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Authors: | Muñoz-Muñoz Jose Luis Garcia-Molina Francisco Varon Ramón Tudela Jose Garcia-Cánovas Francisco Rodríguez-López Jose N |
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Affiliation: | GENZ: Grupo de Investigación Enzimología, Departamento de Bioquímica y Biología Molecular-A, Facultad de Biología, Universidad de Murcia, Espinardo, Murcia, Spain. |
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Abstract: | 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 S(A) 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 S(B) substrates, which include those whose o-quinone evolves with no clear stoichiometry (catechol, 4-methylcatechol, phenol and p-cresol) and, lastly, type S(C) substrates, which give rise to stable o-quinones (4-tert-butylcatechol/4-tert-butylphenol). |
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