Bile acids characteristic features

The common bile acids and salts possess a characteristic molecular structure shown schematically for sodium cholate in Fig. 1 [7]. In contrast to the all irons arrangement of the alicyclic ring systems in alio bile salts, a crucial feature of the... 

The characteristic features of the coliforms are non-sporing, Gram-negative rods, which are bile tolerant and able to ferment lactose at 37 °C producing acid and gas within 48 hours. The term faecal coliform was used to describe coliforms capable of fermenting lactose to acid and gas within 24 hours at 44 °C. The term thermotolerant coliforms is now used more commonly in the UK, although the term faecal coliform is still widely used elsewhere. It should be pointed out that not all thermotolerant coliforms are faecal in origin. 

Figure 19.10 shows a structural formula for cholic acid, a constituent of human bile. The molecule is shown as an anion, because it would be ionized in bile and intestinal fluids. Bile acids, or, more properly, bile salts, are synthesized in the liver, stored in the gallbladder, and secreted into the intestine, where their function is to emulsify dietary fats and thereby aid in their absorption and digestion. Furthermore, bile salts are the end products of the metabolism of cholesterol and, thus, are a principal pathway for the elimination of that substance from the body. A characteristic structural feature of bile salts is a cis fusion of rings A/B. 

Feature of 24-hydroxy-C27 tetrahydroxy-bile acid Base peaks in A in C27 trihydroxy-bile acid Feature of 24-hydroxy-C27 trihydroxy-bile acid Base peaks in A in C27 trihydroxy-bile acid Prominent in 22-hydroxy-CDCA Characteristic of 3,6,7-trihydroxy structures... 

Base peak in 3P-hydroxy-5-cholestanoate Characteristic of oxo-monohydroxy-C24 structure Feature of C-6 hydroxy bile acids Low intensity in bile acid glucuronides Prominent ion in THCA... 

The occurrence of a species-specific bile acid in pig bile [Haslewood (1) Haslewood and Sjovall (2)] and of two such acids in rat bile [Bergstrom and Sjovall (3) Hsia et al. (4) Matschiner et al. (5)] was observed almost simultaneously. After their isolation and characterization, these acids were found to be isomeric 3a,6,7-trihydroxy-5/5-cholanic acids. The acid from pig bile was named hyocholic acid [Haslewood (6) Ziegler (7)], and the two acids from rat bile were named a- and /3-muricholic acids [Hsia et al. (8)]. The fourth isomer of these glycols was identified as a metabolite of hyodeoxycholic acid (3rt,6a-dihydroxy-5 9-cholanic acid) in the rat [Matschiner et al. (9, 10)], and was named ry-muricholic acid [Hsia et al. (8)]. The vicinal glycol structures in ring B of these acids are unique features, but even more unique are their species-specific characteristics which are particularly demonstrated in the metabolic pathways that lead to their formation. 

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