The molecule is a bilin that consists of 8,12-bis(2-carboxyethyl)-18-ethyl-3-ethylidene-2,7,13,17-tetramethyl-2,3-dihydrobilin bearing two oxo substituents at positions 1 and 19. It has a role as a phytochrome chromophore.
3-[(2Z,5Z)-2-[[3-(2-carboxyethyl)-5-[(Z)-[(3Z)-3-ethylidene-4-methyl-5-oxopyrrolidin-2-ylidene]methyl]-4-methyl-1H-pyrrol-2-yl]methylidene]-5-[(4-ethyl-3-methyl-5-oxopyrrol-2-yl)methylidene]-4-methylpyrrol-3-yl]propanoic acid