Thermodynamic Aspects of Fatty Acids Binding to Human Serum Albumin : A Microcalorimetric Investigation

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Thermodynamic parameters have been evaluated for the binding interaction between human serum albumin (HSA) and unbranched fatty acids (FFA) on the basis of a flow microcalorimetric measurement at pH 7.4 and 37℃ by computer-fitting to single- and two-class binding models. The heat of binding increased exothermically with increasing alkyl chain length. FFA with nine or less carbons bound to only one class of binding sites (n=2) with a binding constant (K) of 10^4M^<-1>. FFA with ten or more carbons bound to the first class of binding sites with high affinity K in the order of 10^5 to 10^6M^<-1>, and to the second class with a lower affinity and high capacity. The free energy change of first class of binding sites (ΔG_1) became more negative as the chain length of FFA was increased. The enthalpy change per mol of FFA (ΔH) decreased at the rate of -7.47kJ・mol^<-1>・CH_2^<-1> to a minimum at C9 and then increased due to the hydrophobicity of alkyl chains. Compensation analysis for the i th class of HSA molecule by plotting molar changes of enthalpy (ΔH_<mi>) against entropy (ΔS_<mi>) and free energy (ΔG_<mi>) indicates two distinct binding sites. The first class (i=1) of the long-chain FFA on HSA is an entropy-driven reaction associated with nearly constant values of ΔH_<m1> (-43.0±4.8kJ・mol^<-1>), slightly negative values of ΔS_<m1> (-47.4≦ΔS_<m1>≦-8.1J・mol^<-1>・K^<-1>) and -ΔG_<m1> values, increasing with increasing alkyl chain length. The second class (i=2) of the long-chain FFA may lie in the same region as the binding sites of the short- and medium-chain FFA with a linear relationship between ΔH_<mi>-ΔS_<mi>.
公益社団法人日本薬学会の論文
1992-06-25

Thermodynamic Aspects of Fatty Acids Binding to Human Serum Albumin : A Microcalorimetric Investigation

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