A CIRCULAR-DICHROISM (CD) STUDY OF THE CONSECUTIVE BINDING OF SERUM-ALBUMIN TO BILIRUBIN - POSSIBLE IMPLICATIONS FOR THE BILIRUBIN LEVEL

Binding studies on bovine serum albumin (BSA) with bilirubin (BR) have been performed under physiological conditions using circular dichrois m (CD) and electronic absorption spectroscopy (W-VIS), Analysis of dat a obtained from solutions at varying BSA/BR ratios (R), overall concen trations and pH suggests the coexistence of two similarly strong compl exes with 1:1 stoichiometry (K-ass,K-M ca. 1 x 10(7) dm(3) mol(-1)). F urther binding to BSA affords associates for which a 2:1 stoichiometry (K-ass,K-B ca, 5 x 10(4) dm(3) mol(-1), pH = 7.4) is proposed, Result s indicate that these aggregates comprise the main transport form of B R under physiological conditions. The role of the differently compound ed BSA-BR complexes for controlling the concentration of unbound BR in the plasma is discussed. preliminary experiments performed on human s erum albumin (HSA) are in line with an analogous complexing behaviour.