MD. Reazul Islam and Hideyuki Kurihara
Naturally occurring bromophenols and commercially available halogenated phenols were investigated kinetic inhibition study and a comparison of inhibitory activity against mushroom tyrosinase. All four bromophenols investigated showed noncompetitive inhibition from the results of Lineweaver-Burk plots. The inhibitors may bind another site of the active site and combine with either free enzyme or enzyme-substrate complex. Among them, inhibition constants of symmetric bromophenol dimers, bis(2,3-dibromo-4,5-dihydroxyphenyl)methane and bis(2,3-dibromo-4,5-dihydroxybenzyl)ether, exhibited low values compared to ones of asymmetric dimers. Additionally, 2,3-dibromo-6-(2,3-dibromo-4,5-dihydroxybenzyl)-4,5-dihydroxybenzyl methyl ether showed the most potent inhibition among the compounds investigated. Chlorinated phenols, 2,4-dichlorophenol and 2,2’-methylenebis-(4-chlorophenol), exhibited moderate inhibition against mushroom tyrosinase among commercially available phenols. These results suggest that inhibition of halogenated phenols against mushroom tyrosinase requires a catechol moiety and/or halogen substitution in the one ortho-position of phenolic hydroxy group and vacant substitution in the other ortho-position.
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