Substrate inhibition competes with halide inhibition in polyphenol oxidase
Substrate inhibition competes with halide inhibition in polyphenol oxidase
复制标题
多酚氧化酶中的底物抑制与卤化物抑制竞争
DOI：
10.1007/s10930-012-9442-5
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
Y. Imura and E. Yoshimura
中科院分区：
文献类型：
--
作者：
G.G. Lim;Y. Imura and E. Yoshimura
多酚氧化酶（PPO）是食品工业中重要的普遍存在的酶。尽管 PPO 活性在儿茶酚浓度高达 1 mM 时遵循 Michaelis-Menten 动力学，但在儿茶酚浓度高于 2 mM 时，其活性缓慢下降。这一结果表明，除了活性位点（位点A）外，该酶还具有第二个儿茶酚结合位点（位点B），对PPO活性产生抑制作用。卤化物抑制 PPO 活性的方式是，当卤化物浓度增加时，底物抑制会减弱。此外，儿茶酚浓度的升高降低了卤化物的抑制程度。这些发现表明卤化物也与位点 B 结合以抑制 PPO 活性。稳态动力学分析表明，儿茶酚和 PPO 之间的解离常数取决于卤化物与位点 B 的结合。当氯化物与该位点结合时，解离常数最大。溴化物和碘化物按此顺序产生较低的解离常数。这些数据表明卤化物与位点B的结合调节了位点A的结构，从而发挥抑制作用。
Polyphenol oxidase (PPO) is a ubiquitous enzyme important in the food industry. Although PPO activity followed Michaelis–Menten kinetics at catechol concentrations of up to 1 mM, it slowly decreased at catechol concentrations above 2 mM. This result indicated that in addition to the active site (site A), the enzyme possesses a second catechol-binding site (site B) that exerts an inhibitory effect on PPO activity. Halides inhibit PPO activity in such a way that substrate inhibition is lessened when halide concentration is increased. Furthermore, elevated concentrations of catechol diminished the degree of inhibition by halides. These findings suggest that halides also bind to site B to inhibit PPO activity. A steady-state kinetic analysis demonstrated that the dissociation constant between catechol and PPO depended on the binding of halides to site B. The dissociation constants were greatest when chloride bound to the site. Bromide and iodide yielded lower dissociation constants, in that order. These data indicate that the binding of halide to site B modulated the structure of site A, thereby exerting an inhibitory effect.