Members of this family adopt a structure consisting of four alpha helices and six beta sheets, in an alpha-beta-alpha-alpha-alpha-beta-beta-beta-beta-beta arrangement. They contain a catalytic active site, capable of reducing the gamma-methene bridge of the open tetrapyrrole, biliverdin IX alpha, to bilirubin with the concomitant oxidation of a NADH or NADPH cofactor [1].

1: Crystal structure of a biliverdin IXalpha reductase enzyme-cofactor complex. Whitby FG, Phillips JD, Hill CP, McCoubrey W, Maines MD; J Mol Biol. 2002;319:1199-1210. PMID:12079357