title: The binding isotherms for the interaction of 5-doxyl stearic acid with bovine and human albumin.
abstract: Binding isotherms for the interaction of 5-doxyl stearic acid with bovine and human albumin are reported. The critical micelle concentration (CMC) and the limiting solubility of 5-doxyl stearic acid were determined using the electron spin resonance (ESR)-spin label method. The CMC and the limiting solubility of this spin-label stearic acid in saline-phosphate buffer are 3.5 x 10(-5) M and 2 x 10(-4) M, respectively. We found no ESR line width evidence for pre-association of the spin-label stearate below the CMC. Maximum binding of the spin-label stearate to both bovine and human albumin occurs before micelle formation. The binding isotherm for spin-label stearic acid interaction with bovine albumin is in agreement with data obtained by others using [1-(14)C]stearic acid. For human albumin, comparison is difficult since previous data obtained with [1-(14)C]stearic acid vary widely. Comparison of the ESR 2T(||) values (the splitting between low and high field extremes, a measure of the degree of immobilization of protein-bound spin-label stearate) for bovine and human albumin indicates a greater immobilization of the spin-label molecules bound to human albumin. The binding data indicate that complexes are formed with bound spin-label stearate/albumin ratios of at least 18. The computed equilibrium constants for both bovine and human albumin indicate that the first seven spin-label molecules are tightly bound, log K > 5.0. The species predicted to form in solution by these equilibrium constants are reported.
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D007700:Kinetics; D010080:Oxazoles; D011485:Protein Binding; D012709:Serum Albumin; D012710:Serum Albumin, Bovine; D013113:Spin Labels; D013229:Stearic Acids; D013696:Temperature
chemical_list: D010080:Oxazoles; D012709:Serum Albumin; D013113:Spin Labels; D013229:Stearic Acids; D012710:Serum Albumin, Bovine