3a,6b,7b-Trihydroxy-5b-cholanoic acid, also known as beta-muricholic acid, is a bile acid. 3a,6b,7b-Trihydroxy-5b-cholanoic acid belongs to the class of compounds known muricholic acids in which the hydroxy groups at positions 6 and 7 both have a beta configuration. It is also classified as a 6beta-hydroxy steroid, a 7beta-hydroxy steroid, a steroid acid and a bile acid. Muricholic acids are a group of bile acids that are particularly abundant in mice, which gives them their name. Muricholic acids are also found at low concentrations in other mammalian species, including humans (PMID: 12543708). Muricholic acids differ from the primary bile acids found in humans (which are cholic acid and chenodeoxycholic acid) by having a hydroxyl group in the beta-conformation at the 6-position. The orientation of the hydroxyl group at the 7 position defines alpha- or beta-muricholic acid. Muricholic acids are detectable at low concentrations in human urine (PMIDL 1629271). The enzyme responsible for the 6-hydroxylation reactions forming muricholates in rodents is the cytochrome P450 Cyp2c70. This produces alpha-muricholic acid from chenodeoxycholic acid, and beta-muricholic acid from ursodeoxycholic acid.  Bile acids, such as muricholic acid, are steroid acids found predominantly in the bile of mammals. The distinction between different bile acids is minute, depending only on the presence or absence of hydroxyl groups on positions 3, 6, 7, and 12. Bile acids are physiological detergents that facilitate excretion, absorption, and transport of fats and sterols in the intestine and liver. Bile acids are also steroidal amphipathic molecules derived from the catabolism of cholesterol. They modulate bile flow and lipid secretion, are essential for the absorption of dietary fats and vitamins, and have been implicated in the regulation of all the key enzymes involved in cholesterol homeostasis. Bile acids recirculate through the liver, bile ducts, small intestine and portal vein to form an enterohepatic circuit. They exist as anions at physiological pH and, consequently, require a carrier for transport across the membranes of the enterohepatic tissues. The unique detergent properties of bile acids are essential for the digestion and intestinal absorption of hydrophobic nutrients. Bile acids have potent toxic properties (e.g. membrane disruption) and there are a plethora of mechanisms to limit their accumulation in blood and tissues (PMID: 11316487, 16037564, 12576301, 11907135).