Hemopexin binds -

Ans. is 'a' i.e., Heme* Heme is a metal containing tetrapyrrole ring, linked by methylene or methenyl bridges.* It is a component of hemoglobin, myoglobin, cytochrome proteins* Major form of heme in our body is haemoglobin. In haemoglobin, the metal in the centre is Fe2+. It is surrounded by four pyrrole rings linked by methylene bridges* Heme is released into circulation from RBCs following oxidative stress in the form of hematin* Hematin has Fe3+ in the centre of tetrapyrrole rings.* This non protein bound hematin is cytotoxic as the iron in the centre can act as a Fenton's reagent generating free radicals* These free radicals cause lipid peroxidation of membranes of cells and organelles, protein and DNA damage. This induces apoptosis of cells* To avoid such oxidative damage caused by heme, proteins like hemopexin help.HEMOPEXIN* Hemopexin is a glycoprotein which exhibits the highest affinity for free heme* Hemopexin's function is to protect the cell and tissues from oxidstive damage cause by heme. Because hemopexin does not only bind to free heme but also facilitate the uptake of heme into liver by binding to specific receptors on hepatocytes. Hence hemopexin helps in recycling iron and the iron stores are maintained. Hemopexin is also found to cause an upregulation of heme oxygenase 1 enzyme, thereby they facilitate the conversion of heme into bilirubin and biliverdin.