Sk. Patra et Mk. Pal, DICHROIC PROBE OF THE EQUILIBRIUM-CONSTANT OF THE DISTRIBUTION OF BILIRUBIN TO HUMAN AND BOVINE SERUM ALBUMINS, Journal of macromolecular science. Pure and applied chemistry, A34(9), 1997, pp. 1569-1579
We describe here a method to evaluate the equilibrium constant of the
distribution of a ligand, bilirubin, to two different albumins (human
and bovine serum albumins, HSA and BSA) and hence to determine the ass
ociation constant of the ligand to an albumin (in this case HSA) with
the knowledge of the association constant of the ligand to the other-a
lbumin (in this case BSA). The circular dichroic (CD) spectra of bilir
ubin (BR) induced by HSA and BSA are characteristically different. if
in a pre-formed BSA-BR complex HSA is added, the negative bisignate CD
spectrum of BSA-BR progressively changes sign characteristic to that
of HSA-BR (positively bisignate). This change in dichroism has been us
ed to calculate the equilibrium constant K of the process: BSA-BR + HS
A = HSA-BR + BSA, the value of K comes to be 1.25. The individual asso
ciation constant of BSA-BR has been determined fluorimetrically to be
2.7 x 107 M-1. Since, K of the above process must be the ratio of the
individual association constants of HSA-BR and BSA-BR, the association
constant of HSA-BR comes to be 3.37 x 107 M-1.