<prompt> Metabolism of drugs is mostly done by which enzyme-Cytochrome CCytochrome P450Glucronyl transferaseAcetylase  <response>: Ans. is b i.e., Cytochrome P450 o Biotransformation reactions metabolism of drugs can be classified :A. Non-synthetic phase I reactions Metabolism brings about a change in the drug molecule by:1. Oxidation2. Reduction3. Hydrolysis4. Cyclization5. Decyclization The new metabolite may retain biological activity or it may be an inactive metabolite. Oxidation is the most important metabolizing reaction. The most important enzyme for oxidation reaction is cytochrome P450B.Synthetic phase II or conjugation reaction Metabolism involves union of the drug with one of several polar water-soluble endogenous molecules that are products of intermediary metabolism, to form a water-soluble conjugate which is readily eliminated by kidney or, if the molecular weight exceeds 300, in the bile. Phase II metabolism almost invariably terminates biological activity, i.e. metabolites are usually inactive. Reactions are:-1. Acetylation2. Glucuronide conjugation3. Glycine conjugation4. Glutathione conjugation5. Sulfate conjugation6. Methylation7. Neucleotide synthesis 