Evidence for the possible involvement of the Superoxide radicals in the photodegradation of bilirubin.

The photodecomposition of bilirubin follows first order kinetics with a kB value of 12·5 × 10-3 min–1. In the presence of a model system generating superoxide anions, such as xanthine-xanthine oxidase, the kB value was 103 × 10-3 min-1 This ten-fold enhancement of kB 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 ß–carotene and bistidine did not prevent the enhancement of bilirubin oxidation by xanthinexanthine 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.