Quantitative Studies on Competitive Ligand Binding to Bovine Serum Albumin by Use of the Spin Label 5-Doxyl Dodecanoic Acid

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Abstract
The binding of the spin label 5-doxyl dodecanoic acid to bovine serum albumin in phosphate buffer at pH 7.4 was studied by ESR spectroscopy. Free label and label bound to serum albumin could be quantitatively measured and evaluated from the superposition spectra of these 2 species with no previous separation. The efficiency relative to the spin label as competitors for binding to serum albumin was studied with salicylic acid and some fatty acids of medium length. The results were represented by the stoichiometric model involving equilibrium constants Ki, by binding isotherms constructed from the Ki values and by a purely graphical representation of the experimental data points without connection with any special binding model.