Mushroom Tyrosinase: Catalase Activity, Inhibition, and Suicide Inactivation
详细信息 查看全文
- 作者：Francisco Garcí ; a-Molina ; Alexander N. P. Hiner ; Lorena G. Fenoll ; José ; N. Rodrí ; guez-Lopez ; Pedro A. Garcí ; a-Ruiz ; Francisco Garcí ; a-Cá ; novas ; and José ; Tud
- 刊名：Journal of Agricultural and Food Chemistry
- 出版年：2005
- 出版时间：May 4, 2005
- 年：2005
- 卷：53
- 期：9
- 页码：3702 - 3709
- 全文大小：147K
- 年卷期：v.53,no.9(May 4, 2005)
- ISSN：1520-5118
文摘
Mushroom tyrosinase exhibits catalase activity with hydrogen peroxide (H2O2) as substrate. In theabsence of a one-electron donor substrate, H2O2 is able to act as both oxidizing and reducingsubstrate. The kinetic parameters Vmax and Km that characterize the reaction were determined fromthe initial rates of oxygen gas production (V0O2) under anaerobic conditions. The reaction can startfrom either of the two enzyme species present under anaerobic conditions: met-tyrosinase (Em) anddeoxy-tyrosinase (Ed). Thus, a molecule of H2O2 can reduce Em to Ed via the formation ofoxy-tyrosinase (Eox) (Em + H2O2 
Eox), Eox releases oxygen into the medium and is transformedinto Ed, which upon binding another molecule of H2O2 is oxidized to Em. The effect of pH and theaction of inhibitors have also been studied. Catalase activity is favored by increased pH, with anoptimum at pH = 6.4. Inhibitors that are analogues of o-diphenol, binding to the active site coppersdiaxially, do not inhibit catalase activity but do reduce diphenolase activity. However, chloride, whichbinds in the equatorial orientation to the protonated enzyme (EmH), inhibits both catalase anddiphenolase activities. Suicide inactivation of the enzyme by H2O2 has been demonstrated. A kineticmechanism that is supported by the experimental results is presented and discussed.Keywords: Tyrosinase; mushroom; catalase; inhibition; suicide inactivation
Eox), Eox releases oxygen into the medium and is transformedinto Ed, which upon binding another molecule of H2O2 is oxidized to Em. The effect of pH and theaction of inhibitors have also been studied. Catalase activity is favored by increased pH, with anoptimum at pH = 6.4. Inhibitors that are analogues of o-diphenol, binding to the active site coppersdiaxially, do not inhibit catalase activity but do reduce diphenolase activity. However, chloride, whichbinds in the equatorial orientation to the protonated enzyme (EmH), inhibits both catalase anddiphenolase activities. Suicide inactivation of the enzyme by H2O2 has been demonstrated. A kineticmechanism that is supported by the experimental results is presented and discussed.Keywords: Tyrosinase; mushroom; catalase; inhibition; suicide inactivation