THE BINDING OF SALICYLIC ACID AND RELATED SUBSTANCES TO PURIFIED PROTEINS

¹ Department of Pharmacology, The George Washington University School of Medicine, Washington, D. C.

The binding of a series of simple derivatives of benzoic acid to bovine serum albumin has been investigated. Drugs such as salicylic acid and -resorcylic acid exhibit extensive binding, while p-aminosalicylate, gentisate, p-aminobenzoate, salicylamide and acetylsalicylate show little or no interaction. The carboxylic acid group confers the primary binding capacity upon the compounds, but the presence of ortho hydrogen donors or of alkyl substitution may enhance this capacity. Hydrogen donors in the meta or para position decrease binding. Most of the compounds exhibit two types of binding sites, one of relatively high affinity but small in number, a second of low affinity but in greater number. The former appears to be more structure specific.

The nature of the binding sites upon the protein has been investigated by the use of changes in hydrogen ion concentration, and of chemically modified proteins. The binding appears to be predominantly to the epsilon-amino and possibly the guanidino groups of the protein molecule.