THE EXISTENCE OF CONFORMATIONALLY LABILE (PREFORMED) DRUG-BINDING SITES IN HUMAN SERUM-ALBUMIN AS EVIDENCED BY OPTICAL-ROTATION MEASUREMENTS

The ability of certain drugs to induce conformational changes in human serum albumin has been examined by differential optical rotation measurements at 233 nm. At drug: protein molar ratios ([D]/[P]) of unity, the optical rotation increased, decreased or remained the same depending on the drug used. The change in the optical rotatory dispersion (ORD) signal was investigated as a function of the drug concentration. Drug-protein interactions were relatively specific. There exists at least one, and possibly more, stable preformed high affinity sites for the binding of drugs to albumin. At low [D]/[P] ratios, the ORD titration curves suggest that the high affinity sites are conformationally labile and that the albumin molecule is flexible.