Evidence for the possible involvement of the superoxide radicals in the photodegradation of bilirubin

Abstract

The photodecomposition of bilirubin follows first order kinetics with ak B value of 12.5 × 10^-3 min^-1. In the presence of a model system generating superoxide anions, such as xanthine-xanthine oxidase, the k _B value was 103 × 10^-3 min^-1 This ten-fold enhancement ofk B value by xanthine-xanthine oxidase was abolished when the reaction mixture was supplemented with a superoxide ion scavenger- superoxide dismustase. Further, known singlet oxygen quenchers like β -carotene and bistidine did not prevent the enhancement of bilirubin oxidation by xanthine-xanthine oxidase, thereby ruling out the obligatory conversion of Superoxide anion to singlet oxygen. It is concluded that radical oxygen mediated bilirubin degradation might be a natural catabolic route for the bile pigment degradation during oxygen stress.