Effects of fatty acids on two specific drug binding sites on human serum albumin

Two distinct binding sites, I and II, for anionic drugs on human serum albumin have previously been demonstrated using fluorescent probe techniques. 5-Dimethylaminonaphthalene 1-sulfonamide (DNSA) and dansylsarcosine are specific fluorescent probes for sites I and II, respectively. The addition of fatty acids results in differing effects at the two binding sites, and the specificity of site II is lost. The order of potency of various fatty acids in causing these changes is oleic > stearic > linoleic ≥ palmitic, and this is the same as the order of association constants for these fatty acids. It is concluded that chain length and degree of unsaturation determine both binding affinity and the extent to which the fatty acids induce configurational adaptations in the albumin molecule. Furthermore, studies with varying ratios of oleic acid to albumin suggest that the conformational changes induced in the protein are different for each molecule of oleid acid added. Addition of oleic acid at a 3:1 molar ratio with albumin significantly increased the binding of warfarin and DNSA to site I.