Endogenous substrates glucuronidation

System) Tissue Localization Major Endogenous Substrates Glucuronidated"... 

Biotransformation reactions can be classified as phase 1 and phase 11. In phase 1 reactions, dmgs are converted to product by processes of functionalization, including oxidation, reduction, dealkylation, and hydrolysis. Phase 11 or synthetic reactions involve coupling the dmg or its polar metaboHte to endogenous substrates and include methylation, acetylation, and glucuronidation (Table 1). 

Phase II This phase consists of conjugation reactions. If the metabolite from Phase I metabolism is sufficiently polar, it can be excreted by the kidneys. However, many metabolites are too lipophilic to be retained in the kidney tubules. A subsequent conjugation reaction with an endogenous substrate, such as glucuronic acid, sulfuric acid, acetic acid or an amino acid results in polar, usually more water-soluble compounds that are most often therapeutically inactive. Glucuronidation is the most common and the most important conjugation reaction. Neonates are deficient in... 

Reactions of biotransformation of xenobiotics are usually divided into Phase I and Phase II reactions. In Phase I reactions a polar group, such as hydroxyl (-OH), carboxyl (-COOH), thiol (-SH) and amino (-NH2) group, is introduced into the molecule through the reactions of oxidation, reduction and hydrolysis. Metabolites formed can be more toxic than parent compounds (i.e. paraoxon compared to parathion), but some other nontoxic metabolites can be formed as well. In Phase II reactions polar metabolites are conjugated with endogenous substrates such as glucuronides, sulfates, acetates and amino acids, which form hydrosoluble products that can be readily excreted in urine. However, in the case of OPC it is acceptable to divide reactions of biotransformation to activation and detoxication processes. In these metabolic processes significant role have diflerent enzyme... 

Glucuronidation is an important step in the elimination of many important endogenous substances from the body, including bilirubin, bile acids, steroid hormones, thyroid hormones, retinoic acids, and biogenic amines such as serotonin. Many of these compounds are also substrates for sulfonyltransferases (SULTs) (2). 

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