BINDING OF ROSE-BENGAL ONTO BOVINE SERUM-ALBUMIN

The binding of rose bengal (RB) to bovine serum albumin (BSA) occurs w ith both the folded (at pH 7-4) and the unfolded (pH 12.7) forms of BS A. Absorption spectroscopy has revealed an identical red-shift of 15 n m in lambda(max) of RB in presence of BSA both at pH 7.4 and 12.7. The affinity constants (K) at pH 12.7 have been reduced only by 50% in ma gnitude from those at pH 7.4. These lead us to infer that neither disu lphide loops nor buried residues are involved but that the binding of RB occurs at the sites near the surface of BSA. Moreover, the drastic alterations in the near-UV circular dichroism suggest tertiary structu ral changes induced by RB on binding to BSA. The conformational change s at the binding sites of BSA at pH 7-4 and the affinity of RB particu larly towards the exposed residues in BSA at pH 12.7 are the significa nt factors in the binding of RB to BSA.