OXIDATION REACTIONS OF A BOVINE SERUM-ALBUMIN BILIRUBIN COMPLEX - A PULSE-RADIOLYSIS STUDY

Using the technique of pulse radiolysis, oxidation studies of the bovi ne serum albumin-bilirubin (BSA-BR) system with radicals like CCl3OO., N-3(.), (SCN)(2)(.-), Br-2(.-) and OH. generated in neutral and alkal ine medium are reported. In a neutral solution, BSA protects the bound BR very efficiently from the attack of these radicals. The experiment al k/k' Values for the reaction of CCl3OO., N-3(.) and Br-2(.-) radica ls are 2.46, 1.78 and 2.55 respectively, where k and k are the bimolec ular rate constants for the formation of the semi-oxidized BSA and BR radicals respectively. The calculated ratios from our measurements of rate constants k and k' are 0.16, 0.28 and 1.38 for CCl3OO., N-3(.) an d Br-2(.-) respectively. These values indicate protection of BR by BSA from free radical attack. For Br-2(.-) radical-induced oxidation of t he BSA-BR system, a radical transfer from protein to BR was observed. OH. shows very fast adduct formation with both BSA and BR. The bimolec ular rate constant for the formation of BR-OH adducts at PH 8 +/- 0.2 is 9.5 x 10(9) dm(3) mol(-1) s(-1) (540 nm). OH. adds to BSA at neutra l PH with a rate constant of 3.0 +/- 1.0 x 10(10) dm(3) mol(-1) s(-1) (305 nm). In the BSA-BR complex, BSA fully protects BR from OH. attack and the (BSA-BR)-OH adduct further reacts with free BR molecule if pr esent in solution.