cytochrome P450 family 51 and similar cytochrome P450sThis family is composed of cytochrome P450 51 (CYP51 or sterol 14alpha-demethylase) and related cytochrome P450s. CYP51 is the only cytochrome P450 enzyme with a conserved function across animals, fungi, and plants, in the synthesis of essential sterols. In mammals, it is expressed in many different tissues, with highest expression in testis, ovary, adrenal gland, prostate, liver, kidney, and lung. In fungi, CYP51 is a significant drug target for treatment of human protozoan infections. In plants, it functions within a specialized defense-related metabolic pathway. CYP51 is also found in several bacterial species. This family belongs to the large cytochrome P450 (P450, CYP) superfamily of heme-containing proteins that catalyze a variety of oxidative reactions of a large number of structurally different endogenous and exogenous compounds in organisms from all major domains of life. CYPs bind their diverse ligands in a buried, hydrophobic active site, which is accessed through a substrate access channel formed by two flexible helices and their connecting loop.