Pulse Radiolysis of Bilirubin in Aqueous Solution

Abstract

A pulse radiolysis study of bilirubin, the breakdown product of heme, has been made. In aqueous solution at pH 12, short-lived transient spectra have been obtained for reaction of bilirubin with $e{}_{{\rm aq}}{}^{-}$ and OH. Bimolecular rate constants for these reactions have been measured, namely, $k_{{\rm BR}+e{}_{{\rm aq}}{}^{-}}=9.5\times 10^{9} M^{-1} {\rm sec}^{-1}$ and $k_{{\rm BR}+{\rm OH}}=3.45\times 10^{9} M^{-1} {\rm sec}^{-1}$ , and the spectrum of a long-lived product resulting from decay of the bilirubin-OH adduct has been obtained. In addition, solute destruction by OH has been investigated in detail. The transient absorption spectrum for reduction of bilirubin with the H atom at neutral pH has been measured. By measuring the rate of reaction with $e{}_{{\rm aq}}{}^{-}$ in the presence of bovine serum albumin (BSA), the mode of binding of bilirubin to this biologically important compound has been studied.