RED EDGE EXCITATION SHIFT EMISSION SPECTROSCOPIC INVESTIGATION OF SERUM ALBUMINS AND SERUM ALBUMIN-BILIRUBIN COMPLEXES

The microenvironments around the intrinsic and extrinsic fluorophores in bovine and human serum albumins as well as their complexes with bil irubin have been visualized by red edge excitation shift (REES) emmiss ion spectroscopic investigation. The two albumins and their bilirubin complexes in aqueous buffered solutions (pH 7.5) do not exhibit any ap preciable shift in their emission maxima, upon gradual change in excit ation wavelength towards the red edge of their respective absorption b and. The addition of Triton X-100 triggers REES emission in both the f luorophores. The observations suggest that the microenvironment around the flurophores are not so rigid, and even the extrinsic flurophore b ilirubin having two carboxylic acid groups acts as a hydrophobic non-p olar molecule when bound to albumins. The ligand binding domains (rece ptor sites) are large enough and incorporation of Triton X-100 makes t he fluorophore environments rigid and subtle polarity may also be indu ced. Whereas small polar molecules like CHCl3, ANS and L-trp fail to i nduce REES emission in either of the fluorophores. (C) 1997 Elsevier S cience B.V.