Vorum H, Fisker K, Otagiri M, Pedersen A O, Kragh-Hansen U
Department of Medical Biochemistry, University of Aarhus, Denmark.
Clin Chem. 1995 Nov;41(11):1654-61.
Calcium binding to glycated, penicilloylated, acetylated, and normal defatted human serum albumin as well as to mercapt- and nonmercaptalbumin was studied by equilibrium dialysis of radioactive Ca2+. Binding was quantified by five Scatchard constants [ni = 1, (i = 1-4) and n5 = 10]. Glycation resulted in increased k1- and k2-values and unchanged k3-k5-values, whereas penicilloylation increased all five association constants. The increments were greater the more pronounced the modification, and the enhancements caused by penicilloylation were, for the same degree of modification, greater than those produced by glycation. In contrast, acetylation by acetylsalicylate did not affect calcium binding. Likewise, binding to mercapt- and nonmercaptalbumin was the same, a finding showing that the thiol group of cysteine 34 is not important for calcium binding. D-Glucose and penicillin G are known to react with lysine residues of albumin, and the enhancement of binding resulting from glycation or penicilloylation is probably brought about by unspecific electrostatic effects, possibly supplemented by conformational changes of the protein molecule. The relative importance of the three domains of human serum albumin for calcium binding is discussed.
通过放射性Ca2+的平衡透析研究了钙与糖化、青霉素酰化、乙酰化和正常脱脂人血清白蛋白以及与巯基白蛋白和非巯基白蛋白的结合。结合情况通过五个斯卡查德常数[ni = 1，(i = 1 - 4)且n5 = 10]进行定量。糖化导致k1和k2值增加，而k3 - k5值不变，而青霉素酰化则使所有五个缔合常数都增加。修饰越显著，增量越大，并且在相同修饰程度下，青霉素酰化引起的增强作用大于糖化产生的增强作用。相比之下，乙酰水杨酸的乙酰化不影响钙的结合。同样，与巯基白蛋白和非巯基白蛋白的结合情况相同，这一发现表明半胱氨酸34的巯基对钙的结合并不重要。已知D - 葡萄糖和青霉素G会与白蛋白的赖氨酸残基发生反应，糖化或青霉素酰化导致的结合增强可能是由非特异性静电作用引起的，蛋白质分子的构象变化可能对此有补充作用。文中讨论了人血清白蛋白三个结构域对钙结合的相对重要性。
