Tang Ning, Skibsted Leif H
Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK 1958 Frederiksberg C, Denmark.
Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK 1958 Frederiksberg C, Denmark.
Food Res Int. 2016 Nov;89(Pt 1):749-755. doi: 10.1016/j.foodres.2016.10.002. Epub 2016 Oct 5.
Zinc amino acid or peptide complexes improve zinc absorption, however, the thermodynamics behind the interaction between zinc ion and these potential ligands is not well characterized. Therefore, binding of zinc to amino acids, peptides and whey proteins were investigated by isothermal titration calorimetry to provide useful information for improving zinc bioavailability which is lowered by many food components like phytate. Zinc binding to lactoferrin and to bovine serum albumin was found exothermic with ∆H=-100kJ/mol and -30kJ/mol, respectively, in aqueous 0.16M NaCl of pH7.4 at 25°C by isothermal titration calorimetry, while binding to α-lactalbumin and β-lactoglobulin was slightly endothermic. Still the binding constant was for all four proteins found to have a value around 2×10L/mol indicating enthalpy-entropy compensation as also confirmed for zinc binding to amino acids with cysteine being enthalpically favored, while serine<histidine<glutamate<phosphorylated serine increasingly were found entropically favored. The enthalpy-entropy compensation makes whey proteins more homogeneous as zinc vehicles counteracting concentration fluctuation and precipitation of zinc.
锌氨基酸或肽复合物可提高锌的吸收，然而，锌离子与这些潜在配体之间相互作用背后的热力学特性尚未得到充分表征。因此，通过等温滴定量热法研究了锌与氨基酸、肽和乳清蛋白的结合，以提供有助于提高锌生物利用率的有用信息，因为许多食物成分（如植酸盐）会降低锌的生物利用率。通过等温滴定量热法发现在25°C、pH7.4的0.16M NaCl水溶液中，锌与乳铁蛋白和牛血清白蛋白的结合是放热的，∆H分别为-100kJ/mol和-30kJ/mol，而与α-乳白蛋白和β-乳球蛋白的结合则略有吸热。不过，发现所有四种蛋白质的结合常数约为2×10L/mol，这表明存在焓-熵补偿，锌与氨基酸结合时也证实了这一点，半胱氨酸在焓方面更有利，而丝氨酸<组氨酸<谷氨酸<磷酸化丝氨酸在熵方面越来越有利。焓-熵补偿使乳清蛋白作为锌载体更加均匀，可抵消锌的浓度波动和沉淀。
