Ashbrook J D, Spector A A, Santos E C, Fletcher J E
J Biol Chem. 1975 Mar 25;250(6):2333-8.
The binding of six physiologically important long chain fatty acids to defatted human plasma albumin was measured at 37 degrees in a calcium-free Krebs-Ringer phosphate buffer, pH 7.4. The data were analyzed in terms of multiple stepwise equilibria. With the saturated acids, the magnitude of the equilibrium (association) constants, Ki, increased as the chain length increased: laurate smaller than myristate smaller than palmitate smaller than stearate. Oleate was bound more tightly than stearate; by contrast, linoleate was bound less tightly than stearate. The equilibrium constants, K1 through K12, ranged from 2.4 times 10-6 - 3.5 times 10-3 m-1 for laurate to 2.6 times 10-8 - 3.5 times 10-5 m-1 for oleate. Successive values of Ki decrease for each of the acids, indicating that major cooperative binding effects do not occur over the physiological range of fatty acid concentrations. In no case could the Ki be segregated into distinct classes, suggesting that any grouping of albumin binding sites is somewhat arbitrary. The results were inconclusive concerning whether premicellar association of unbound fatty acid occurs. Although corrections for premicellar association produced very little change in the Ki values for myristate, they raised the Ki for palmitate and stearate by 300 to 700 per cent. A sigmoidal relationship was obtained when the logarithm of Ki was plotted against chain length for the saturated fatty acids containing 6 to 18 carbon atoms, indicating that the binding energy is not simply a statistical process dependent only on the fatty acid chain length. This selectivity that albumin contributes to the binding process may be due to varying degrees of configurational adaptability of its binding sites as the fatty acid increases in length.
在37摄氏度、pH值为7.4的无钙磷酸缓冲液（Krebs-Ringer phosphate buffer）中，测定了六种生理上重要的长链脂肪酸与脱脂人血浆白蛋白的结合情况。数据依据多步逐步平衡进行分析。对于饱和脂肪酸，平衡（缔合）常数Ki的大小随链长增加而增大：月桂酸小于肉豆蔻酸小于棕榈酸小于硬脂酸。油酸比硬脂酸结合更紧密；相比之下，亚油酸比硬脂酸结合更松散。平衡常数K1至K12，月桂酸的范围为2.4×10⁻⁶ - 3.5×10⁻³ m⁻¹，油酸的范围为2.6×10⁻⁸ - 3.5×10⁻⁵ m⁻¹。每种酸的Ki连续值都降低，表明在脂肪酸浓度的生理范围内不存在主要的协同结合效应。在任何情况下，Ki都不能被分成不同类别，这表明白蛋白结合位点的任何分组都有些随意。关于未结合脂肪酸的前胶束缔合是否发生，结果尚无定论。尽管对前胶束缔合的校正使肉豆蔻酸的Ki值变化很小，但使棕榈酸和硬脂酸的Ki值提高了300%至700%。当绘制含6至18个碳原子的饱和脂肪酸的Ki对数与链长的关系图时，得到了一个S形关系，这表明结合能不仅仅是一个仅依赖于脂肪酸链长的统计过程。白蛋白对结合过程的这种选择性可能是由于随着脂肪酸链长增加，其结合位点的构型适应性程度不同。
