Bilirubin interaction with ganglioside: possible mechanism in kernicterus

Reaction of bilirubin with increasing amounts of ganglioside purified from neonatal brain significantly alters the spectral absorption of bilirubin in proportion to the quantity of ganglioside added. Increments in absorbance occur at 353 nm with a prompt but transient increase at 486 nm. A decrease in absorbance occurs which is most marked at 447 nm. When gangliosides are added to bilirubin (9.1 mug/ml or 0.016 muM/ml), the decrease in absorbance is essentially linear up to the highest concentration of purified ganglioside tested (182 mug/ml or 0.097 muM/ml), which represents a molar ratio of 6.1:1. The asymptotic nature of the bilirubin-ganglioside reaction as measured by the decrease in absorbance with time suggests a stoichiometric relationship between the two substances. An isosbestic point was demonstrated at 405 nm. Observations reported here suggest bilirubin reaction with ganglioside is at least a two-step process.