Tyrosinase Catalyzes Asymmetric Sulfoxidation super([dagger])

• Published in: Biochemistry (Easton) Vol. 47; no. 11; pp. 3493 - 3498
• Main Authors: Pievo, Roberta, Gullotti, Michele, Casella, Luigi, Monzani, Enrico
• Format: Journal Article
• Language: English
• Published: 01.01.2008
• ISSN: 0006-2960
• DOI: 10.1021/bi702421b

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 ( similar to 20%) but high enantioselectivity ( similar to 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 super(18)O sub(2) 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.