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首页> 外文期刊>Food Hydrocolloids >Interactions between casein layers adsorbed on hydrophobic surfaces from self consistent field theory: k-casein versus para-k-casein
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Interactions between casein layers adsorbed on hydrophobic surfaces from self consistent field theory: k-casein versus para-k-casein

机译：根据自洽场理论，酪蛋白层吸附在疏水表面上的相互作用：k-酪蛋白与对-k-酪蛋白

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Interactions mediated by layers of K-casein and para-K-casein have been calculated and compared using the self consistent field (SCF) approach, at pH and electrolyte concentrations found in milk. Our results show the interaction potentials at close separation distances to be repulsive for K-casein, while they are attractive for para-K-casein. We have also studied K-casein chains stripped of their sugar moieties and highlighted the important role that the carbohydrate side chains play in the provision of steric forces. The point of transition from a repulsive to an attractive interaction is found to be rather sensitive to the degree of coverage of the surface by the protein chains. At Γ = 0.0025 chains per unit monomer area, the value is just over 40% renneted chains, whereas at Γ = 0.0032 this increases to 87%. At the coverage values higher than those we estimate for the surface of casein micelles, no transition is detected and the interactions remain repulsive even when all of K-casein has been converted to para-K-casein, as already shown by Mellema, Leermakers, and de Kruif (1999). At lower surface coverage values, the interaction potential curves for otherwise uncharged surfaces, covered with para-K-casein, posses an energy barrier. We have demonstrated that the origin of this energy barrier is electrostatic, with para-K-casein contributing a net positive charge to the surface. We have also explored the importance of the asymmetry in the distribution of charge between the para-K-casein and the glycomacropeptide sides of the protein. The glycomacropeptide is net negative while para-K-casein side is net positive at neutral pH. Our results suggest that on a negatively charged surface, such as the surface of casein micelles, this uneven distribution of charge is just as important in determining the conformation of K-casein chains as is the difference in the hydrophobic and hydrophilic nature of the two sides of this protein.
机译：在牛奶中发现的pH值和电解质浓度下，已使用自洽场（SCF）方法计算并比较了由K-酪蛋白和对K-酪蛋白层介导的相互作用。我们的结果表明，相距很近的相互作用势对K-酪蛋白具有排斥性，而对对K-酪蛋白具有吸引力。我们还研究了剥去糖部分的K-酪蛋白链，并强调了碳水化合物侧链在提供空间力中的重要作用。发现从排斥相互作用到吸引相互作用的转变点对蛋白质链对表面的覆盖程度相当敏感。在Γ= 0.0025链每单位单体面积时，该值刚好超过40％的网纹链，而在Γ= 0.0032时，该值增加到87％。正如Mellema，Leermaker和Cosman所证明的那样，当覆盖率值高于我们估计的酪蛋白胶束表面的覆盖率值时，即使所有K-酪蛋白都已转化为对K-酪蛋白，也未检测到过渡，相互作用仍然相互排斥。 and de Kruif（1999）。在较低的表面覆盖率值下，原本不带电的表面（被对K-酪蛋白覆盖）的相互作用电势曲线具有能垒。我们已经证明了这种能垒的起源是静电的，对-K-酪蛋白为表面贡献了净正电荷。我们还探讨了对-K-酪蛋白与蛋白质的糖巨肽侧之间电荷分布不对称的重要性。在中性pH下，糖巨肽为净阴性，而对-K-酪蛋白侧为净阳性。我们的结果表明，在带负电荷的表面（例如酪蛋白胶束的表面）上，这种电荷的不均匀分布对于确定K-酪蛋白链的构象同样重要，与两侧疏水和亲水性质的差异同样重要这种蛋白质。

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