Glucuronidation conjugates, types

FIGURE 7.2 Examples of various types of glucuronide conjugates. 

These studies indicate 1) fermentable fiber increases the total number of viable anaerobic bacteria in the cecum, but not the stomach or small intestine of rats 2) the microfloral capacity for hydrolysis of glucuronide conjugates, for nitroreduction, and for azoreduction is elevated in fermentable fiber-fed rats 3) this increased capacity for microfloral metabolism of nitrobenzene and dinitrotoluene is correlated with an elevation in the toxicity of these nitroaromatics 4) the role fiber plays in the modulation of chemical toxicity is a function of the fiber-type and the structure of the toxicant. 

Three new monoterpenoid lactones, (28)—(30), isolated from the urine of koala bears fed on Eucalyptus punctata, appear to have arisen from the cyclization of carboxylic acids formed as hydrolysis products of glucuronide conjugates from the metabolism of a- and /3-pinenes.70 Linalool injected into various plant species has been claimed to be converted into a-terpineol and other monoterpenoids.71 However, direct interconversions cannot be inferred from this type of non-radioactive tracer study. The terpenoids alleged to be produced may well be stress metabolites or be formed b secondary processes that perturb the usual pattern of terpenoid formation. 

Except for the recognized generalizations that glucosides are found in plants and glucuronides are found in animals, it is difficult to establish a consistent correlation of conjugate type and species. 

Mobile-phase additives are known to play an important role in the efficient separation of chromatographic peaks in LC-MS. Mobile-phase additives used for LC-MS studies are most often volatile molecules that can be easily evaporated in the LC-MS interface to prevent ionization suppression and/or detection contamination. The most commonly used mobile-phase additives in LC-MS analysis are the small organic acids, acetic and formic acids, together with their ammonium salts. Trifluoroacetic acid (TFA) is also widely used in LC-MS analysis despite reports of ionization suppression in the ESI mode. Some studies suggest that the drawback of TFA use can be overcome for some neutral analytes by using minute concentrations of the acid in the mobile phase. A number of studies presented here used TFA as the mobile-phase additive, and in all those instances, ESI was the ionization interface. However, formic acid was the additive most commonly used, followed closely by TFA and then by the ammonium salts of both formic and acetic acid. The type of glucuronide conjugate (O vs. N) did not appear to influence the type of mobile-phase additive used. 

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