Taurocholic acids, structure

A related protein, MRP3, has similar structure to this mutated MRP2 and can transport taurocholic acid but mutation of the equivalent residue, leucine 1084, with lysine-blocked transport of taurocholic acid. In cholestasis there is an induction of MRP3 mRNA suggesting that this transporter is active, at least when bile-acid concentrations are raised within the hepatocyte. This transporter function is shown in Figure 2.1. 

The structures of the salts of glycocholic acid and taurocholic acid are ... 

The structure of cholic acid helps us understand how bile salts such as sodium taurocholate promote the transport of lipids through a water-rich environment. The bottom face of the molecule bear s all of the polar groups, and the top face is exclusively hydrocarbon-like. Bile salts emulsify fats by forming micelles in which the fats are on the inside and the bile salts are on the outside. The hydrophobic face of the bile salt associates with the fat that is inside the micelle the hydrophilic face is in contact with water on the outside. 

Figure 7.13 shows some of the structures of common bile acids. In low ionic strength solutions, sodium taurocholate forms tetrameric aggregates, with critical... 

Figure 4.14 Structures of cholic and chenodeoxycholic acids which are the acids that form the bile salt The asterisk indicates the position at which an ester bond is formed with taurine or glycine so that bile salts are taurocholate, chenodeoxytaurocholate, gly-cocholate, and glycochenodeoxycholate are formed. The structure of taurine is H2NCH2CH2SO3 and glycine is H2NCH2COOH.

The taurine residue can also be found as an amide derivative of the 26-carboxylic acid function in the 3p,5a,6p,15a-polyhydroxylated steroids 328 and 329, which were obtained from the starfish Myxoderma platyacanthum [245]. The structures of both compounds were determined from spectral data and chemical correlations. The bile of the sunfish Mola mola has been shown to contain a new bile acid conjugated with taurine (330) together with sodium taurocholate. Compound 330 was identified as sodium 2-[3a,7a, 11 a-trihydroxy-24-oxo-5P-cholan-24-yl]amino]ethane-sulfonate on the basis of its physicochemical data and chemical transformations [246]. 

Primary bile acids generally exist in bile in the form of conjugates with glycine or taurine through a peptide bond. These water-soluble conjugates, by virtue of their surface active properties, solubilize lipophilic substances in the gut, forming micelles in the process. The structures of two such compounds, glycocholic (XIII) and taurocholic (XIV) acids, are shown in Fig. 8. 

Simple micelles, composed only of bile salts, have a limited capacity to solubilize cholesterol. With taurocholate for example, one molecule of cholesterol is solubilized by 25 molecules of bile salt, while addition of a monoglyceride to the preparation essentially doubles the solubilization of cholesterol[17]. Obviously, the participation of additional amphipaths and amphiphiles, such as phospholipids and fatty acids, in the micellar structure causes dramatic increases in sterol solubility (from 100-1000 fold)[48]. 

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