Tyrosinase Catalyzes Asymmetric Sulfoxidation

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• 作者：Roberta Pievo ; Michele Gullotti ; Enrico Monzani ; Luigi Casella
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：March 18, 2008
• 年：2008
• 卷：47
• 期：11
• 页码：3493 - 3498
• 全文大小：109K
• 年卷期：v.47,no.11(March 18, 2008)
• ISSN：1520-4995

文摘

Mushroom tyrosinase was found to catalyze the oxidation of organic sulfides to sulfoxides in the presence of a catechol as cosubstrate, in a reaction which is unprecedented for this enzyme and resembles those performed by external monooxygenases. Only the oxy form of the enzyme is in fact capable of oxidizing the sulfide in a two-electron process, while the resulting met form can only be recycled by reduction with catechol. The cosubstrate competes with the sulfide also in the reaction with oxy-tyrosinase. For this reason, the sulfoxidation of thioanisole in the presence of L-3,4-dihydroxyphenylalanine (L-dopa) occurs with moderate yields (~20%) but high enantioselectivity (~85% e.e.), and favors (S)-methyl phenyl sulfoxide. The enantioselectivity can be further increased to >90% when excess ascorbic acid is added to the reaction to limit enzyme inactivation by the quinones produced by L-dopa oxidation. An experiment using ¹⁸O₂ showed that 18-O incorporation into methyl phenyl sulfoxide was above 95%, confirming that the mechanism of the sulfoxidation involves oxygen transfer from oxy-tyrosinase to the sulfide.