Which of the following is not a part of phase I reaction? (DNB Dec 2011)
- Guanyl cyclase is not a secondary massager but an enzyme that mediates the conversion of guanosine triphosphate (GTP) to 3',5'-cyclic guanosine monophosphate (cGMP) and pyrophosphate ((BG Katzung, Basic and Clinical Pharmacology; 10th Edition’ 2007, pp-25).
- Glucoronidation is most common phase-II reaction and the bond formed between phase-I metabolite and phase-II endogenous product is covalent by nature.
- Hence, the drug after glucoronidation is eliminated. It increases the tendency of the drug to be eliminated by bile.
It is an important mechanism of making the drug water soluble. Phase-I reactions include, oxidation, reduction, hydrolysis and cyclization. These typically include CYP 450, NADPH and oxygen (BG Katzung, Basic and Clinical Pharmacology; 10th Edition’ 2007, pp-54-55).