Biliverdins

Biliverdins are a group of bile pigments derived from heme. They are linear tetrapyrroles produced when heme oxygenase opens the heme ring to form biliverdin IXα (the most abundant isomer) and related isomers such as IXβ, IXγ, and IXδ. Biliverdin IXα is subsequently reduced by biliverdin reductase to bilirubin IXα, a key step in heme catabolism.

In mammals and other animals, biliverdin is produced in the liver and reticuloendothelial tissues and is excreted in bile; it gives a green color to bruises and to bile. Biliverdin and bilirubin can function as antioxidants; bilirubin is normally conjugated and excreted. Excess biliverdin is typically quickly converted to bilirubin or excreted.

Plants and some microorganisms use biliverdin IXα as a precursor to phytochromobilin, the chromophore of plant phytochromes. In plants, HY2 enzyme reduces biliverdin to phytochromobilin, enabling light sensing.

Properties: Biliverdin is a green tetrapyrrole pigment; it absorbs in the blue-green region and can be fluorescent under certain conditions. In research, biliverdin is used as a substrate for near-infrared fluorescent proteins (iRFPs) that derive their chromophore from biliverdin.

Summary: Biliverdins are the coordinated family of heme-derived pigments with roles in heme catabolism, coloration, redox biology, and as a biosynthetic precursor to key photoreceptors in plants.