SPECIES DIFFERENCE IN COMPETITIVE BINDING OF 2-(4'-HYDROXYBENZENEAZO)BENZOIC ACID (HBABA) AND ALPHA-(4-CHLOROPHENOXY)-ALPHA-METHYLPROPIONIC ACID (CPMPA) TO SERUM ALBUMIN . A POSSIBLE MODEL SYSTEM FOR STUDYING ALLOSTERIC TRANSITIONS

The comparative competitive binding of 2-(4′-hydroxybenzeneazo)benzoic acid (HBABA) and α-(4-chlorophenoxy)-α-methylpropionic acid (CPMPA) with a number of serum albumin preparations obtained from different species was studied. Data derived from equilibrium dialysis, spectrophotometric, and extrinsic rotatory dispersion (ERD) measurements reveal a unique behavior for rat serum albumin (RSA). With serum albumins obtained from all other species studied CPMPA competitively inhibited the HBABA-protein interaction al all concentration levels. With RSA low concentrations of CPMPA actually enhanced the HBABA-protein interaction. These results suggest that CPMPA is able to cause a small molecular perturbation in the RSA molecule which liberates additional sites on the protein for HBABA binding. Rat albumin, in combination with certain drugs, seems to be a model for studying allosteric transitions. © 1969, American Chemical Society. All rights reserved.