Use of fluorescence enhancement technique to study bilirubin-albumin interaction

Bilirubin-albumin solution gave an emission spectrum in the wavelength rang e 500-600 nm with emission maxima at 528 nm when excited at 487 nm. The mag nitude of fluorescence intensity increased on increasing bilirubin/albumin molar ratio. At three different albumin concentrations, namely, 1.0, 2.5 an d 10.0 mu M, there was an initial linear increase in fluorescence up to a m olar ratio 1.0 in all cases beyond which it sloped off or decreased. This f luorescence enhancement was used to calculate the binding parameters of bil irubin-albumin interaction and the value of binding constant was found to b e 1.72 x 10(7) l/mol similar to the published values obtained with other me thods. Different serum albumins, namely, human (HSA), goat (GSA), pig (PSA) and dog serum albumins (DSA) bound bilirubin with almost the same affinity when studied by the technique of fluorescence enhancement. Bilirubin-album in interaction was also studied at different pH and ionic strengths. There was a decrease in bilirubin-albumin complex formation on either decreasing the pH from 9.0 to 7.0 or increasing the ionic strength from 0.15 to 1.0. T hese results suggest that the technique of fluorescence enhancement can be used successfully to study the bilirubin-albumin interaction. (C) 1999 Else vier Science B.V. All rights reserved.