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A New Look on Protein-Polyphenol Complexation during Honey Storage: Is This a Random or Organized Event with the Help of Dirigent-Like Proteins?

机译:蜂蜜储存过程中蛋白质-多酚复合物的新外观:这是类似Dirigent的蛋白质的随机或有组织的事件吗?

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摘要

Honey storage initiates melanoidin formation that involves a cascade of seemingly unguided redox reactions between amino acids/proteins, reducing sugars and polyphenols. In the process, high molecular weight protein-polyphenol complexes are formed, but the mechanism involved remains unknown. The objective of this study was twofold: to determine quantitative and qualitative changes in proteins in honeys stored for prolonged times and in different temperatures and to relate these changes to the formation of protein-polyphenol complexes. Six -month storage decreased the protein content by 46.7% in all tested honeys (t-test, p<0.002) with the rapid reduction occurring during the first three month. The changes in protein levels coincided with alterations in molecular size and net charge of proteins on SDS –PAGE. Electro-blotted proteins reacted with a quinone-specific nitro blue tetrazolium (NBT) on nitrocellulose membranes indicating that quinones derived from oxidized polyphenols formed covalent bonds with proteins. Protein-polyphenol complexes isolated by size-exclusion chromatography differed in size and stoichiometry and fall into two categories: (a) high molecular weight complexes (230–180 kDa) enriched in proteins but possessing a limited reducing activity toward the NBT and (b) lower molecular size complexes (110–85 kDa) enriched in polyphenols but strongly reducing the dye. The variable stoichiometry suggest that the large, “protein-type” complexes were formed by protein cross-linking, while in the smaller, “polyphenol-type” complexes polyphenols were first polymerized prior to protein binding. Quinones preferentially bound a 31 kDa protein which, by the electrospray quadrupole time of flight mass spectrometry (ESI-Qtof-MS) analysis, showed homology to dirigent-like proteins known for assisting in radical coupling and polymerization of phenolic compounds. These findings provide a new look on protein-polyphenol interaction in honey where the reaction of quinones with proteins and polyphenols could possibly be under assumed guidance of dirigent proteins.
机译:蜂蜜储存会引发类黑素形成,涉及氨基酸/蛋白质,还原糖和多酚之间看似无指导的氧化还原反应。在此过程中,形成了高分子量的蛋白质-多酚复合物,但所涉及的机制仍然未知。这项研究的目的是双重的:确定长时间存储在不同温度下的蜂蜜中蛋白质的数量和质量变化,并将这些变化与蛋白质-多酚复合物的形成联系起来。在所有测试的蜂蜜中,六个月的储存使蛋白质含量降低了46.7%(t检验,p <0.002),并且在头三个月迅速减少。蛋白质水平的变化与SDS-PAGE上蛋白质分子大小和净电荷的变化相吻合。电印迹蛋白与硝酸纤维素膜上的醌特定硝基蓝四唑(NBT)反应,表明衍生自氧化多酚的醌与蛋白形成共价键。通过大小排阻色谱法分离的蛋白质-多酚复合物的大小和化学计量不同,分为两类:(a)富含蛋白质但对NBT还原活性有限的高分子量复合物(230–180 kDa)分子量较低的复合物(110-85 kDa)富含多酚,但会强烈还原染料。可变的化学计量比表明,大的“蛋白质型”复合物是通过蛋白质交联形成的,而较小的“多酚型”复合物是在蛋白质结合之前首先聚合多酚的。醌优先结合一个31 kDa的蛋白质,该蛋白质通过电喷雾四极杆飞行时间质谱(ESI-Qtof-MS)分析显示与已知有助于协助酚类化合物的自由基偶联和聚合的类似dirigant的蛋白质具有同源性。这些发现为蜂蜜中蛋白质与多酚的相互作用提供了新的视角,其中假设醌与蛋白质和多酚的反应可能是在稀疏蛋白质的指导下进行的。

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