Interaction of human serum albumin with charge transfer probe ethyl ester of N,N-dimethylamino naphthyl acrylic acid: an extrinsic fluorescence probe for studying protein micro-environment.

The charge transfer (CT) probe ethyl ester of N,N-dimethylamino naphthyl acrylic acid (EDMANA) bound to Human Serum Albumin (HSA) serves as an efficient reporter of the polarity and conformational changes of protein in aqueous buffer (Tris-HCl buffer, pH=7.03) and in presence of denaturant, quencher and reverse micelles. The change in fluorescence intensity and the position of emission maxima of EDMANA in presence of HSA well reflect the nature of binding and location of the probe inside the proteinous environment. The increase in steady state anisotropy values with increase of protein concentration indicate restriction imposed on the mobility of the probe molecules in the proteinous medium. The results of fluorescence quenching of EDMANA by acrylamide, Fluorescence Resonance Energy Transfer (FRET) and Red Edge Excitation Shift (REES) studies throw light on the accessibility to the probe bound to HSA and hence indicate the probable location of the probe within the hydrophobic cavity of HSA. The complicated nature of protein unfolding in presence of urea is well studied by change in the fluorescence properties of EDMANA bound to HSA protein.