Mechanistic implications of variable stoichiometries of oxygen consumption during tyrosinase catalyzed oxidation of monophenols and o-diphenols

Marı́a José Peñalver , Alexander N.P. Hiner , José Neptuno Rodrı́guez-López , Francisco Garcı́a-Cánovas , José Tudela
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引用次数: 16

Abstract

The stoichiometry of oxygen consumption during tyrosinase-catalyzed oxidation of an o-diphenol (4-tert-butylcatechol, TBC) and a monophenol (4-tert-butylphenol, TBP) has been determined. At high [substrate]/[enzyme] ratios, in the case of o-diphenols, the stoichiometry of the enzyme-catalyzed reaction was always 1 O2/2 o-diphenols, although if the o-quinone product was unstable, the apparent stoichiometry could tend to 1 O2/1 o-diphenol due to regeneration of an o-diphenol in a side reaction. In the case of monophenols, the stoichiometry could be 1 O2/1 monophenol or 1.5 O2/1 monophenol depending if the o-quinone product was stable or unstable, respectively. However, at low [substrate]/[enzyme] ratios, the oxygen/substrate stoichiometry could, even in the case where stable products are formed, be lower than 1 O2/2 substrates for o-diphenols or higher than 1 O2/1 substrate for monophenols. These data supported the mechanism proposed by Rodrı́guez-López et al. [J. Biol. Chem. 267 (1992) 3801–3810], in which, during hydroxylation of monophenols, tyrosinase first transformed monophenol to o-diphenol and then either catalyzed a further oxidation to form o-quinone or released it into the reaction medium. In this second case, subsequent oxidation of the o-diphenol resulted in additional oxygen consumption.

酪氨酸酶催化单酚和邻二酚氧化过程中氧消耗的可变化学计量学的机制含义
测定了酪氨酸酶催化氧化邻二酚(4-叔丁基儿茶酚,TBC)和单酚(4-叔丁基酚,TBP)过程中耗氧量的化学计量学。在高[底物]/[酶]比的情况下,邻二酚的酶催化反应的化学计量量始终为1 O2/2邻二酚,尽管如果邻醌产物不稳定,由于邻二酚在副反应中再生,表观化学计量量可能倾向于1 O2/1邻二酚。在单酚的情况下,根据邻醌产物是稳定的还是不稳定的,化学计量可以分别为1 O2/1单酚或1.5 O2/1单酚。然而,在低[底物]/[酶]比率下,即使在形成稳定产物的情况下,氧/底物化学计量也可能低于邻二酚的1 O2/2底物,或高于单酚的1 O2/1底物。这些数据支持了rodriguez guez-López等人提出的机制[J]。医学杂志。化学,267(1992)3801-3810],其中,在单酚羟基化过程中,酪氨酸酶首先将单酚转化为邻二酚,然后催化进一步氧化形成邻醌或将其释放到反应介质中。在第二种情况下,随后的邻二酚氧化导致额外的氧气消耗。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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