Cytochrome P450 monooxygenases carry out most Phase I biotransformation reactions. Which pair of substrates must be supplied for the CYP450 enzyme system to insert one atom of oxygen into a xenobiotic molecule?
- A Molecular oxygen (O2) and NADH
- B Molecular oxygen (O2) and NADPH ✓
- C Hydrogen peroxide and NADPH
- D Water and FADH2
Correct answer: B. Molecular oxygen (O2) and NADPH
Explanation
The CYP450 system is a mixed-function oxidase: one atom of molecular oxygen enters the substrate (as hydroxyl group) and the other is reduced to water, with electrons donated by NADPH via NADPH-cytochrome P450 reductase. NADH can feed electrons through cytochrome b5 only as a secondary helper, never as the primary donor, so option A is incorrect. Hydrogen peroxide is a product of uncoupled reactions, not a required substrate.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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