<unk>  consists of an open chain tetrapyrrole. It is formed by oxidative cleavage of a porphyrin in heme, which affords<unk> verdin.<unk> verdin is reduced to<unk> . After conjugation with glucuronic acid,<unk>  is excreted.<unk>  is structurally similar to the pigment phycobilin used by certain algae to capture light energy, and to the pigment phytochrome used by plants to sense light. All of these contain an open chain of four pyrrolic rings. Like these other pigments, some of the double-bonds in<unk>  isomerize when exposed to light. This isomerization is relevant to the phototherapy of jaundiced newborns: the E,Z-isomers of<unk>  formed upon light exposure are more soluble than the unilluminated Z,Z-isomer, as the possibility of intramolecular hydrogen bonding is removed. Increased solubility allows the excretion of unconjugated<unk>  in<unk> e. Some textbooks and research articles show the incorrect geometric isomer of<unk> . The naturally occurring isomer is the Z,Z-isomer.
Bilirubin
Lumirubin
Bile acid
Uric acid
Lipoprotein
Blood protein
Hemoglobin
Alanine transaminase