Molecular Pharmacology, Vol 5, 244-252, Copyright © 1969 by the American Society for Pharmacology and Experimental Therapeutics

Optical Studies of Drug-Protein Complexes

II. Interaction of Phenylbutazone and Its Analogues with Human Serum Albumin

¹ Laboratory of Chemical Pharmacology, National Heart Institute, National Institutes of Health, Bethesda[unknown] Maryland 20014

The binding of phenylbutazone to human serum albumin generated a positive ellipticity band at 287 mµ in the circular dichroic spectrum of time protein. This extrinsic Cotton effect resulted from perturbation of the carbonyl chromophore of phenylbutazone by an asymmetrical locus at the albumin binding site. Hydrophobic interactions appeared to be important for the maintenance of a rigid drug-protein complex, since the introduction of hydrophilic groups into phenylbutazone caused considerable reduction in the magnitude of induced optical activity. Phenylbutazone competitively displaced 1-dimethylamino-naphthalene-5-sulfonyl-N-glycine (a fluorescent probe for the hydrophobic regions of proteins) from human serum albumin. This suggested that there was a hydrophobic area at or near one of the phenylbutazone-binding sites. The red shift in the ultraviolet absorption maximum of phenylbutazone on binding to albumin provided some evidence that the phenyl groups of the drug were located in a region of the protein where the dielectric constant was less than that of water.