Which enzyme is primarily involved in Phase I metabolism?

Which enzyme is primarily involved in Phase I metabolism?

• A. Cytochrome P450
• B. UDP-Glucuronosyltransferase
• C. Glutathione S-Transferase
• D. Sulfotransferase

Answer: (A)

Phase I metabolism involves adding or exposing a functional group on the drug to prepare it for conjugation. The primary players here are the cytochrome P450 enzymes, a family of heme-containing monooxygenases that carry out oxidation, reduction, and sometimes hydrolysis of many drugs. This functionalization often makes the molecule more reactive and sets the stage for Phase II, where conjugation occurs to increase water solubility for elimination. Examples of Phase II enzymes include UDP-glucuronosyltransferases, glutathione S-transferases, and sulfotransferases, which attach polar groups to the Phase I metabolites. Because the main job of Phase I is functionalization via oxidation and related reactions, cytochrome P450 enzymes are the key players.

Phase I metabolism involves adding or exposing a functional group on the drug to prepare it for conjugation. The primary players here are the cytochrome P450 enzymes, a family of heme-containing monooxygenases that carry out oxidation, reduction, and sometimes hydrolysis of many drugs. This functionalization often makes the molecule more reactive and sets the stage for Phase II, where conjugation occurs to increase water solubility for elimination. Examples of Phase II enzymes include UDP-glucuronosyltransferases, glutathione S-transferases, and sulfotransferases, which attach polar groups to the Phase I metabolites. Because the main job of Phase I is functionalization via oxidation and related reactions, cytochrome P450 enzymes are the key players.