title: Effect of catechol-thiol conjugates on tyrosinase-dependent tyrosine hydroxylation.
abstract: 1. The tyrosinase reaction in the presence of a thiol compound was studied using mushroom tyrosinase (EC 1.10.3.1) with regard to catechol-thiol conjugates. 2. Although tyrosine hydroxylation of tyrosinase was extremely decreased in the presence of a thiol compound, the inhibitory effect was removed by the addition of a pyrocatechol-cysteine conjugate, S-(2,3-dihydroxyphenyl) cysteine, which was not oxidized by the enzyme. 3. The pyrocatechol-cysteine conjugate was also able to shorten the lag period of tyrosinase-dependent tyrosine hydroxylation. 4. The sigmoidal reaction curve of tyrosine hydroxylation observed in the presence of sulfhydryl compounds was found to be caused by the catechol-thiol conjugates, the final products of the enzyme reaction, which counteract the inhibitory effect of sulfhydryl compounds. 5. The pyrocatechol-cysteine conjugate, on the other hand, was shown to cause the decrease of the reaction rate of the enzyme during incubation.
mesh_terms: D001487:Basidiomycota / Q000201:enzymology; D004156:Catechol Oxidase / Q000378:metabolism*; D002396:Catechols / Q000494:pharmacology*; D003545:Cysteine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005978:Glutathione / Q000494:pharmacology*; D006900:Hydroxylation; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D002396:Catechols; D014443:Tyrosine; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; D005978:Glutathione; D003545:Cysteine