Multiple competitive displacement interactions involving human serum albumin, anticoagulants, oleic acid and various drugs

Variation in the binding affinity of warfarin and phenprocoumon to human serum albumin in relation to surgery

The binding equilibria of warfarin and phenprocoumon with defatted human serum albumin were studied by equilibrium dialysis in 33 mM sodium phosphate buffer, pH 7.4, 37 degrees C. The binding isotherms for both ligands were consistent with binding to two similar and independent sites in the albumin molecule. The binding affinity of warfarin was markedly increased on adding palmitic acid up to palmitate 4 mol per mol albumin and then it decreased. The binding affinity of phenprocoumon varied similarly but to a lesser degree. Serum samples were obtained from 14 patients undergoing knee joint surgery, six consecutive samples from each patient. The binding affinity of warfarin and phenprocoumon added in low concentrations to the serum samples was consistently less than to purified albumin. The binding affinity for warfarin increased slightly with increasing fatty acid concentrations during surgery, but the increase was much less than expected from the in vitro studies. The binding of phenprocoumon in the serum samples was not influenced by changing fatty acid concentration. The binding affinity for both drugs decreased markedly during the three days following surgery.

Multiple cobinding of two ligands to serum albumin: a stoichiometric description of binding equilibria

Binding equilibria for simultaneous binding of several molecules of two anionic ligands, sulfamethizole/warfarin in one series and sulfamethizole/diflunisal in another, to human serum albumin were studied by equilibrium dialysis. It was found that Klotz's stepwise binding equilibrium concept, extended to cover interaction of two ligands with one carrier, could be used for a quantitative description of binding equilibria. Reciprocity of ligand effects was established at all levels. Heterotropic anticooperativity was present among these pairs of ligands. The experiments were supplemented with observations of albumin binding equilibria for traces of warfarin in the presence of varying amount of oleate, up to 6 mol/mol albumin, by measuring dialysis rates for unbound warfarin. Binding of warfarin to albumin is enhanced upon binding of oleate up to 4 mol/mol albumin, and decreases at higher oleate concentrations. Using stoichiometric (stepwise) binding constants for oleate previously published by Ashbrook et al. [(1975) J. Biol. Chem. 250, 2333-2338], the reverse effect, of warfarin on binding of oleate, was calculated. Simultaneous binding of these ligands to albumin could be described according to the stoichiometric principles as used above for sulfamethizole/warfarin and sulfamethizole/diflunisal.

Binding of branched-chain 2-oxo acids to bovine serum albumin

1. Binding of branched-chain 2-oxo acids to defatted bovine serum albumin was shown by gel chromatography and equilibrium dialysis. 2. Equilibrium-dialysis data suggest a two-side model for binding in Krebs-Henseleit saline at 37 degrees C with n1 = 1 and n2 = 5. Site association constants were: 4-methyl-2-oxovalerate, k1 = 8.7 x 10(3) M-1, k2 = 0.09 x 10(3) M-1; 3-methyl-2-oxovalerate, k1 = 9.8 x 10(3) M-1, k2 = 0.08 x 10(3) M-1; 3-methyl-2-oxobutyrate, k1 = 1.27 x 10(3) M-1, k2 = less than 0.05 x 10(3) M-1. 3. Binding of 4-methyl-2-oxovalerate to defatted albumin in a phosphate-buffered saline, pH 7.4, gave the following thermodynamic parameters: primary site delta H0(1) = -28.6kJ . mol-1 and delta S0(1) = -15.2J . mol-1 . K-1 (delta G0(1) = -24.0kJ . mol-1 at 37 degrees C) and secondary sites delta H0(2) = -25.4kJ . mol-1 and delta S0(2) = -46.1J . mol-1 . K-1 (delta G0(1) = -11.2kJ . mol-1 at 37 degrees C). Thus binding at both sites is temperature-dependent and increases with decreasing temperature. 4. Inhibition studies suggest that 4-methyl-2-oxovalerate may associate with defatted albumin at a binding site for medium-chain fatty acids. 5. Binding of the 2-oxo acids in bovine, rat and human plasma follows a similar pattern to binding to defatted albumin. The proportion bound in bovine and human plasma is much higher than in rat plasma. 6. Binding to plasma protein, and not active transport, explains the high concentration of branched-chain 2-oxo acids leaving rat skeletal muscle relative to the concentration within the tissue, but does not explain the 2-oxo acid concentration gradient between plasma and liver.