Spectral investigations of the interactions of eosine blue and rose bengal with bovine serum albumin

Abstract

The spectrophotometric investigation of the binding of two structurally resembling halogen-substituted fluorescein dyes, eosine blue (EB) and rose bengal (RB), to bovine serum albumin (BSA) at <em>p</em>H 7.4 has resulted in the observance of a single complex for EB but two types of complexes, one absorbing at 540 nm (comp-1) and the other at 555 nm (comp-2), for RB. The analysis of the dependence of binding constant <em>(K) </em> on [BSA] has revealed the binding of EB by ligand-facilitated self-association mechanism. In the case of RB, <em>K </em> has been found to be independent of [BSA] for comp-l but has showed inverse dependence on [BSA] for comp-2, the mechanisms of binding for both these complexes being different from that of EB-BSA interaction. Moreover, it has been noticed that surface bound comp-1 of RB-BSA is stronger than the interior bound comp-2, i.e., <em>K _comp-1</em> > <em>K</em> _comp-2, which could be explained by the bulkiness of EB in preventing its effective interaction with the hydrophobic interior of BSA. Thus contrasting binding mechanisms in the interaction of structurally similar dyes can be monitored.