Bilirubin IXalpha is a member of the class of biladienes that is a linear tetrapyrrole with the dipyrrole units being of both exovinyl and endovinyl type. A product of heme degradation, it is produced in the reticuloendothelial system by the reduction of biliverdin and transported to the liver as a complex with serum albumin. It has a role as an antioxidant, a human metabolite and a mouse metabolite. It is a member of biladienes and a dicarboxylic acid. It contains a 24G7 epitope. It is a conjugate acid of a bilirubin(2-).