To prevent enzymatic browning, applying a polyphenol oxidase (PPO) inhibitor is more desirable, especially when the freshness of the product matters. Most of the inhibition studies were done on mushroom tyrosinase (MT) while the literature indicates that MT and PPO of Solanum tuberosum (PPO_sol) respond differently to the same modulator despite their similar active sites. This research was conducted to deepen our knowledge about PPO_sol and introduce a more specific inhibitor for this enzyme to be used in controlling the enzymatic browning of potatoes. A modified procedure was developed for PPO_sol purification. The enzyme was subjected to some essential physicochemical and kinetics studies. In parallel to the comparable physicochemical properties, homology modeling revealed high structural similarity between Solanum lycopersicum PPO (PPO_sly) and PPO_sol except for their active site pockets. Accordingly, PPO_sol showed 5.1- and 34-fold higher affinity toward chlorogenic acid compared with two PPO_sly isozymes. Alike PPO_sly, PPO_sol showed monophenolase activity but it was inactive toward L-tyrosine and p-coumaric acid. Based on structural criteria, phthalic acid, cinnamic acid, ferulic acid, and vanillin were selected and thoroughly examined for inhibition of the catecholase activity of PPO_sol. Although all these substances inhibited PPO_sol in mixed-inhibition mode, the results were strongly in favor of vanillin with IC₅₀ < 1.37 mM and K_i < 1.2 mM.

中文翻译：

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通过对马铃薯多酚氧化酶活性和抑制的结构洞察，开发更特异的马铃薯多酚氧化酶抑制剂

为了防止酶促褐变，更需要使用多酚氧化酶 (PPO) 抑制剂，尤其是当产品的新鲜度很重要时。大多数抑制研究是对蘑菇酪氨酸酶 (MT) 进行的，而文献表明马铃薯的MT 和 PPO (PPO _sol ) 对同一调节剂的反应不同，尽管它们的活性位点相似。进行这项研究是为了加深我们对 PPO_溶胶的了解，并为这种酶引入一种更具体的抑制剂，用于控制马铃薯的酶促褐变。为 PPO_溶胶开发了一种改进的程序纯化。对该酶进行了一些必要的物理化学和动力学研究。与可比较的物理化学性质平行，同源性建模揭示了番茄PPO (PPO _sly ) 和 PPO_溶胶之间的高度结构相似性，除了它们的活性位点口袋。因此，与两种 PPO _sly同工酶相比，PPO_溶胶对绿原酸的亲和力高 5.1 倍和 34 倍。类似 PPO _sly , PPO_溶胶显示出单酚酶活性，但对 L-酪氨酸和对香豆酸无活性。根据结构标准，选择了邻苯二甲酸、肉桂酸、阿魏酸和香草醛，并彻底检查了对 PPO_溶胶儿茶酚酶活性的抑制作用。尽管所有这些物质都以混合抑制模式抑制 PPO_溶胶，但结果强烈支持香草醛，IC ₅₀ < 1.37 mM 和K _i < 1.2 mM。