title: Effects of aliphatic fatty acids on the binding of Phenol Red to human serum albumin.
abstract: Binding of Phenol Red to human serum albumin at pH 7.0 was studied by ultrafiltration (n1 = 1, K1 = 3.9 X 1-(4) M-1, n2 = 5, K2 = 9.6 X 10(2) M-1). The presence of 1 mol of octanoate or decanoate per mol of albumin caused a decrease in dye binding (dye/protein molar ratio 1:1), which, in contrast with additional fatty acid, was very pronounced: 1-8 mol of palmitate or stearate resulted in a small, and apparently linear, displacement of Phenol Red. The displacement effect of 1-5 mol of oleate, linoleate or linolenate per mol of albumin was comparable with that of the equimolar concentrations of palmitate or stearate. A higher molar ratios the unsaturated acids caused a drastic decrease in dye binding. The different Phenol Red-displacement effects of low molar ratios of medium-chain and long-chain fatty acids indicate that these acids have different high-affinity binding sites. In accordance with this proposal, low concentrations of stearate had only a small effect on the Phenol Red-displacement effect of octanoate. Phenol Red-binding curves in the presence of 1 mol of octanoate, 8 mol of stearate and 6 or 7 mol of linolenate per mol of albumin respectively indicated that the dye and the fatty acids do not complete for a common primary binding site. In contrast, a secondary Phenol Red-binding site could be identical with the primary octanoate-binding site. Furthermore, the primary Phenol Red-binding site could be the same as a secondary linolenate-binding site. Assignment of the different primary binding sites for Phenol Red and for medium-chain and long-chain fatty acids to a model of the secondary structure of albumin is attempted.
mesh_terms: D001665:Binding Sites; D002210:Caprylates / Q000494:pharmacology; D005227:Fatty Acids / Q000494:pharmacology*; D006801:Humans; D008042:Linolenic Acids / Q000494:pharmacology; D008956:Models, Chemical; D010635:Phenolphthaleins / Q000378:metabolism*; D010637:Phenolsulfonphthalein / Q000378:metabolism*; D011487:Protein Conformation; D012709:Serum Albumin / Q000378:metabolism*; D013228:Stearates / Q000494:pharmacology
chemical_list: D002210:Caprylates; D005227:Fatty Acids; D008042:Linolenic Acids; D010635:Phenolphthaleins; D012709:Serum Albumin; D013228:Stearates; D010637:Phenolsulfonphthalein