EFFECT OF CATECHOL-THIOL CONJUGATES ON TYROSINASE DEPENDENT TYROSINE HYDROXYLATION

概要

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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 sulf hydryl compounds was found to be caused by the catechol-thiol conjugates, the final products of the enzyme reaction, which counteract the inhibitory effect of sulf hydryl 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.
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