Drug interactions. VII. The fatty acid binding properties of bovine serum albumin.

Abstract

The interrelationships between fatty acid and probe binding to bovine serum albumin (BSA) were investigated by a fluorescence method, using 1-anilinonaphthalene-8-sulfonate (ANS) and N-phenyl-1-naphthylamine (NPN) as fluorescent probes. The fatty acidinduced quenching of probe fluorescence is probably due to the displacement of probes from BSA binding sites. It appears that NPN and ANS are bound to BSA at the same sites. Various molar ratios of capric acid, lauric acid and palmitic acid were added to defatted BSA in the presence of ANS, and the association constants of the fatty acids were calculated. Measurements of ANS fluorescence (λmax 465nm) and the fluorescence (λmax 340nm) of the ANS-BSA complex as well as the circular dichroism spectra of BSA in the presence of fatty acids in pH 7.4 phosphate buffer indicated that fatty acids induce different conformational states of the albumin molecule. One of the strongest binding sites of long-chain fatty acids may be the site which is labeled by TNBS (2, 4, 6-trinitrobenzenesulfonic acid), located in the carboxyl-terminal half of the molecule, which does not contain tryptophan residues. It is suggested that the mechanism of inhibition of the probe-BSA binding by capric acid may involve competition for the same binding sites. In contrast, the decreases in probe binding with BSA in the presence of lauric acid. palmitic acid or stearic acid are due not only to a displacement of the probes by fatty acids from the probebinding sites but also to a simultaneous conformational change of the probe-binding sites caused by the interaction of the probes and fatty acids.