Abstract
Equilibrium dialysis, ultrafiltration and frontal analysis gel chromatography have been shown to produce comparable results for the binding, to bovine serum albumin, of a number of drugs with markedly different degrees of binding and physico-chemical properties. The binding of sodium salicylate to rat serum has been studied by in vivo dialysis and the results shown to be in good agreement with those obtained by in vitro ultrafiltration. The binding of a series of aliphatic carbamates to bovine serum albumin has been used to study the importance of hydrophobic bonding in small molecule-protein interactions. Binding was found to be directly correlated with the lipophilic character of the carbamates and associated with negative free energy and positive entropy changes. A model is proposed to account for the fluorescence observations on the binding of the carbamates to albumin. Warfarin has been shown to be a fluorescent probe and this property used to investigate the nature of its interaction with different species and preparations of albumin. The binding site of warfarin on albumin was shown to be located in a hydrophobic region of the protein and its binding suggested to involve the amino acid residues;lysine, tyrosine and histidine. Differences in the affinity and nature of the binding sites were apparent for the interaction of warfarin with rat, human and bovine (crystalline and fraction V) albumins. Binding was found to occur through one primary binding site for all species, except perhaps for bovine albumin (fraction V). Approximately eight secondary sites were apparent for all albumins. Good agreement was found for the fluorescence of warfarin between rat and human albumins and serums. The potential of the fluorescent probe technique to evaluate drug displacement from protein binding sites was demonstrated. l-Anilino-8-naphthalenesulphonate and the novel fluorescent probes warfarin (R+ and S- isomers) and benzidine, together with difference spectra, have been used to investigate the nature of the hepatic Microsomal cytochrome P-450 binding sites(type I, type II and Reverse type I). The type I and Reverse type I sites were found to be closely associated and appear to be in a hydrophobic environment, whereas the type II was hydrophilic in nature. The binding of R(+) warfarin presents and interesting species difference being type I in the hamster, but Reverse type I in the rat. The binding of these fluorescent probes to albumin and microsomal protein has been compared and the binding sites found to be located in similarly hydrophilic or hydrophobic environments.