Inactivation Kinetics of Mushroom Tyrosinase in the Dimethyl Sulfoxide Solution

Q.-X. Chen^*, X.-D. Liu, and H. Huang

Key Laboratory of the Ministry of Education for Cell Biology and Tumor Cell Engineering, Department of Biology, School of Life Sciences, Xiamen University, Xiamen 361005, People's Republic of China; fax: +86-592-2185487; E-mail: chenqx@jiangxian.xmu.edu.cn

^* To whom correspondence should be addressed.

Received August 5, 2002; Revision received October 9, 2002

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Mushroom tyrosinase (EC 1.14.18.1) is a kind of copper-containing oxidase that catalyzes both the hydroxylation of tyrosine into o-diphenols and the oxidation of o-diphenols into o-quinones and then forms brown or black pigments. In the present paper, the effects of dimethyl sulfoxide on the enzyme activity for the oxidation of L-3,4-dihydroxyphenylalanine (L-DOPA) have been studied. The results show that low concentrations of dimethyl sulfoxide (DMSO) can lead to reversible inactivation of the enzyme, and the IC₅₀ is estimated to be 2.45 M. Inactivation of the enzyme by DMSO is classified as mixed type. The kinetics of inactivation of mushroom tyrosinase at low concentrations of DMSO solution has been studied using the kinetic method of the substrate reaction. The rate constants of inactivation have been determined. The results show the free enzyme molecule is more fragile than the enzyme-substrate complex in the DMSO solution. It is suggested that the presence of the substrate offers marked protection of this enzyme against inactivation by DMSO.

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KEY WORDS: mushroom tyrosinase, inactivation, kinetics, dimethyl sulfoxide

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