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Menadione-dependent reduction of tertiary amine N-oxide by rat liver cytosol
1Institute of Pharmaceutical Science, Hiroshima University School of Medicine, Japan.
Abstract:
This study demonstrates the menadione-dependent reduction of imipramine N-oxide, a tertiary amine N-oxide, to imipramine by rat liver cytosol in the presence of NADH or NADPH. A mechanism for the cytosolic reduction of the tertiary amine N-oxide is proposed. Menadione is converted to its reduced form by a menadione-reducing enzyme such as DT-diaphorase and the reduced pyridine nucleotide, followed by reduction of the tertiary amine N-oxide to the amine by the heme group of catalytic hemoproteins in the presence of reduced menadione as an electron donor.
Insights
Rat liver cytosol reduces imipramine N-oxide to imipramine using menadione and pyridine nucleotides. A proposed mechanism involves DT-diaphorase and hemoproteins in tertiary amine N-oxide reduction.
Area of Science:
- Biochemistry
- Pharmacology
- Enzymology
Background:
- Tertiary amine N-oxides are metabolites of various drugs and endogenous compounds.
- The reduction of N-oxides is crucial for drug metabolism and detoxification.
- Cytosolic pathways for N-oxide reduction are not fully elucidated.
Purpose of the Study:
- To investigate the menadione-dependent reduction of imipramine N-oxide in rat liver cytosol.
- To elucidate the mechanism of cytosolic tertiary amine N-oxide reduction.
- To identify key enzymes and cofactors involved in this process.
Main Methods:
- Incubation of imipramine N-oxide with rat liver cytosol.
- Addition of reduced pyridine nucleotides (NADH or NADPH) and menadione.
- Enzyme assays to identify menadione-reducing enzymes like DT-diaphorase.
- Spectrophotometric analysis to monitor substrate and product formation.
Main Results:
- Menadione-dependent reduction of imipramine N-oxide to imipramine was observed.
- The reduction required reduced pyridine nucleotides (NADH or NADPH).
- DT-diaphorase was identified as a key menadione-reducing enzyme.
Conclusions:
- A novel cytosolic pathway for tertiary amine N-oxide reduction is proposed.
- This pathway involves menadione, DT-diaphorase, pyridine nucleotides, and hemoproteins.
- This mechanism contributes to the understanding of drug metabolism and N-oxide detoxification.