Bile acids hydrolysis

The two most important bile acids, cholic acid C24H40Os and desoxy-cholic acid C24H40O4, occur in ox bile in combination, partly with glycine and partly with taurine as glyco- and taurocholic and glyco- and tauro-desoxycholic acids. The linkage between the amino acids and the bile acids is of an amide nature. On hydrolysis the nitrogenous constituents are split off. 

This method suffered from sensitivity problems initially as the bile-acid molecules lack a chromophore, but did offer the distinct advantage that conjugated bile acids could be determined without hydrolysis. The sensitivity issue was addressed by use of fluorescent derivatives such as dimethoxycoumarin esters with a C18 reverse phase column and were able to resolve endogenous mixtures of bile acids. The combination of hplc and mass-spectroscopy detection has further improved the sensitivity along with providing specific identification, important as the resolution of bile acids by hplc is not as good as capillary column glc. ... 

Of the systems listed in Table VI, melphalan is most stable in the Burroughs-Wellcome injectable kit. The instructions recommend the use of the solution within 15—30 minutes. According to the manufacturer, 8.5% hydrolysis takes place in 24 hours after mixing [86]. The stability of melphalan increases in acidic solutions and higher temperatures accelerate the hydrolysis. The type and concentration of anionic species present in the solution alter the hydrolysis rate. The formation of the intermediate ionized species is retarded and/or reversed by the presence of chloride ions [9,82,87], resulting in a significantly increased stability [53,87,88]. The stability of melphalan is increased in the presence of bovine serum albumin, human plasma, bile acids, and bile, probably by hydrophobic interactions that make the chloroethyl moiety less accessible to nucleophilic attack [40,62,74,87,89—91]. 

These substrate molecules exhibit a wide variety of chemical structures. Some ABC proteins facilitate the transport of inorganic ions, whereas others pump various organic compounds, including lipids, bile acids, glutathione and glucuronide conjugates, or even short peptides. Most ABC family proteins utilize the energy of ATP hydrolysis for this transport activity (active transporters), but some ABC transporters form specific membrane channels. 

Esters, Carboxylic Acids, and Ethers.—The rates of hydrolysis of 3(3- and 6(3-acetoxy-4 ,5 -epoxides and 1 a-acetoxy-2(3,3 (3-epoxides were observed to be accelerated relative to those acetates not containing a neighbouring epoxide group.24 Bile acid methyl esters were readily prepared from the carboxylic acids by reaction with methanol in the presence of toluene-p-sulphonic acid.25 Bile acids were readily converted into the amino-amides (14) by successive reaction with Bu N-... 

The ll-palm-A -THC can be hydrolyzed to II-OH-A -thc by cholesterol esterase and triacylglycerol lipase but not by phospholipase A, acetylesterase or phosphotransacetylase (16). An attempt to modify the retention of fatty acid-conjugated DDT metabolites was carried out by injecting the DDT-treated rats with sodium salt of various bile acids, heparin or lecithin of which all were known to affect the esterification or ester hydrolysis by the cholesterol esterase system. The results Indicated a significant decrease in the retention of the conjugated DDT metabolites in the rat liver and spleen (17). 

For the quantitative estimation of bile acids in body fluids and tissues, consideration must be given as to whether (1) an extraction step is necessary to partially purify the bile acids prior to further analysis (2) hydrolysis is required to remove glycine and taurine or other conjugate moieties and (3) the method of analysis will be of the required sensitivity and provide infer-... 

To deconjugate bile acids for further analysis, particularly by gas-liquid chromatography, different methods are required for the hydrolysis of the peptide bonds in glycine and taurine conjugates than for hydrolysis of the ester sulfate and glucuronide bonds. Glycine and taurine may be removed by either alkaline or enzymatic hydrolysis (Rll). Alkaline hydrolysis is often... 

Chemical hydrolysis or solvolysis is the only method available at present to remove sulfate groups from bile acids. It is known that some colonic bacteria possess a sulfatase which can utilize sulfated bile acids as substrate (H24), but this enzyme has not yet been purified. The position of the sulfate moiety in monosulfated bile acids is nearly always at C-3 and this group is easily removed by acid hydrolysis in ethereal solution after removal of glycine or taurine (VI). This method, however, does not remove sulfate groups from C-7 or C-12 (PI). For complete removal, other methods have been described, including solvolysis in acidified methanol-acetone for 18 hours at 37°C (P6), acidified ethyl acetate-ethanol for 16 hours at 39 C (A6), or acidified 2,2-dimethoxypropane for 12 hours at room temperature (C3). 

Unlike enzymatic or radioimmunoassay methods, GLC requires lengthy sample preparation before bile acid concentrations can be determined. In the case of serum, bile acids must be extracted (see Section 6.1) and hydrolysis carried out to remove glycine and taurine, and also sul te groups, if they are likely to be present (see Section 6.2). The free bile acids are then converted to volatile derivatives. 

Because HPLC ofiers the possibility of rapid separation, quantification, and recovery of both free bile acids and bile acid conjugates, much interest is currently centered on this technique. A significant advant e of HPLC compared to CLC is that potentially destructive hydrolysis steps can be avoided and bile acid conjugates can be analyzed as they occur in bile or serum. The method is relatively fast as the major bile acids in human bile have been separated in less than 1 hour by reverse-phase HPLC (B25, M8). 

G12. Goto, J., Hasegawa, M., Kato, H., and Nambara, T., A new method for simultaneous determination of bile acids in human bile without hydrolysis. Clin. Chim. Acta 87,141-... 

Rll. Roseleur, O. J., and Van Gent, C. M., Alkaline and enzymatic hydrolysis of conjugated bile acids. Clin. Chim. Acta 66, 269-272 (1976). 

Organic solutes such as nutrients (amino acids, sugars, vitamins, and bile acids), neurotransmitters, and drugs are transferred across cellular membranes by specialized transport systems. These systems encompass integral membrane proteins that shuttle substrates across the membrane by either a passive process (channels, facilitated transporters) or an active process (carriers), the latter energized directly by the hydrolysis of ATP or indirectly by coupling to the cotransport of a counterion down its electrochemical gradient (e.g., Na, ... 

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