Interactions of Xanthine Molecules with Bovine Serum Albumin

The binding of a number of structurally related xanthine compounds by bovine serum albumin was investigated in an attempt to elucidate some of the structural specificities of the interaction. The study included caffeine, theophylline, 8-nitrotheophylline, 8-chlorotheophylline, theophyIline-7-acetic acid, 8-methoxycaffeine, 8-ethoxycaffeine, 8-chlorocaffeine, 8-methylcaffeine, theobromine, 8-nitrotheobromine, uric acid, 1,3,7-trimethyluric acid, uracil, and 1,3-dimethyluracil. Under the conditions employed, interactions between the protein and uric acid, uracil, and dimethyluracil could not be detected. The remaining compounds were bound to varying degrees and evidence was obtained to indicate that a single site on the protein was responsible for the major portion of the binding. Anionic species were generally found to possess much stronger interactive tendencies than those which had no formal charge.