Photo-oxidation and photoprotection in the IXγ bile pigment series: A comparison of the photoprotective roles of pterobilin, phorcabilin and sarpedobilin in vitro

Abstract

Pterobilin ( L9, biliverdin IXγ), a blue green bile pigment from butterflies, is an effective photoprotector of the methylene blue-sensitized photo-oxidation of bilirubin (both as dimethyl esters). The observed effect is of the same order as that observed for the isomerie biliverdins IXα, IXβ, and IXδ ( L4, L8, and L10, respectively). However the dimethyl esters of phorcabilin ( 1) and sarpedobilin ( 2), the cyclized derivatives of pterobilin, are unable to provide photoprotection under the same conditions. The possible significance of this result is considered.