Examples of the phase II reactions are glucuronidation, sulfation, and murcapturic acid formation. Both glucuronidation and sulfation proceed via enzymatic reactions in which, respectively, active glucuronic acid and active sulfate are used. Mercapturic acid formation is an enzymatic process, which results from the conjugation of reactive intermediates with glutathione. The conjugated product is then converted into a mercapturic acid and excreted. Phase II reactions generally result in the formation of compounds that are less biologically active although sometimes they yield products with a higher bioactivity.
Examples are nitrenium, carbonium, and thiiranium ions.
Biotransformation Reactions Biotransformation reactions are enzymatic conversions of lipophilic foreign substances and endogenous metabolic waste products. Phase II reactions consist mostly of conjugation reactions with, for example glucuronic acid, sulfate, or glutathione. Biotransformation reactions can lead to considerable changes in the biological activity of xenobiotics. If the activity is decreased the reaction is considered a bioinactivation or detoxification reaction. If the toxicity is increased it is referred to as a bioactivation reaction.