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Polyamines as modulators of drug oxidation reactions catalyzed by cytochrome P-450 from liver microsomes
Abstract:
The effect of polyamines on the activity of the mixed-function oxidase (MFO) system from human, rat and rabbit liver microsomes was investigated in detail. It was shown that polyamine (spermine) stimulates NADPH-dependent activity of the MFO system several-fold whatever the substrate (foreign drug or natural), not only with microsomes but also with the reconstituted system consisting of highly purified cytochrome P-450 (LM2 isozyme), cytochrome P-450 NADPH reductase and dilauroylphosphorylcholine. Stimulation (extent and concentration dependence) appeared to be dependent on a number of parameters such as ionic strength, pH, animal species and treatment, nature of the substrate, and was stereospecific (different effect on 6 beta-and 16 alpha-testosterone hydroxylation). Further, the spermine effect was evaluated on some elementary steps of the cytochrome P-450 reaction cycle, like substrate binding, P-450 reduction and second electron transfer. Finally, it was shown that the organic peroxide dependent activity was not stimulated by spermine with microsomes nor with the purified P-450 LM2 isozyme. On the basis of this study, it was concluded that the locus of polyamine action is cytochrome P-450 and that stimulation could result either from increased stability of the oxyferrous intermediate of P-450 or from an increased rate of second electron transfer from reductase to P-450.
Insights
Polyamines like spermine significantly boost the liver
Area of Science:
- Biochemistry
- Enzymology
- Pharmacology
Background:
- The mixed-function oxidase (MFO) system, crucial for metabolizing drugs and endogenous compounds, involves cytochrome P-450 enzymes.
- Polyamines are known to interact with nucleic acids and proteins, but their role in MFO activity is less understood.
Purpose of the Study:
- To investigate the detailed effects of polyamines, specifically spermine, on the activity of the liver MFO system.
- To elucidate the mechanism by which polyamines influence MFO activity and identify the specific component involved.
Main Methods:
- Studied the NADPH-dependent MFO activity in liver microsomes from humans, rats, and rabbits.
- Utilized a reconstituted MFO system with purified cytochrome P-450 (LM2 isozyme), NADPH reductase, and lipids.
- Assessed the impact of spermine on various reaction steps, including substrate binding, reduction, and electron transfer.
Main Results:
- Spermine significantly stimulated NADPH-dependent MFO activity across different substrates and species.
- Stimulation was dependent on parameters like ionic strength, pH, substrate, and stereochemistry.
- Spermine did not stimulate organic peroxide-dependent MFO activity, suggesting a specific interaction with the electron transport chain.
Conclusions:
- Polyamines, particularly spermine, act directly on cytochrome P-450 to enhance MFO activity.
- The stimulation mechanism may involve increased stability of the oxyferrous intermediate or enhanced electron transfer from NADPH reductase.