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Published on: March 20, 2018
ON THE MECHANISM OF DRUG HYDROXYLATION IN RAT LIVER MICROSOMES
1Department of Pathology at Sabbatsberg Hospital, Karolinska Institutet, and The Wenner-Gren Institute, University of Stockholm, Stockholm, Sweden.
The Journal of Cell Biology
|October 30, 2009
Summary
This study investigates liver microsomal drug hydroxylation using aminopyrine demethylation. Phenobarbital enhances activity, involving TPNH-cytochrome c reductase and a CO-binding pigment.
Area of Science:
- Biochemistry
- Pharmacology
- Enzymology
Background:
- Liver microsomes possess a TPNH- and O(2)-dependent drug hydroxylation system.
- Phenobarbital administration enhances drug-hydroxylating activity in rats.
Purpose of the Study:
- To elucidate the mechanism of liver microsomal drug hydroxylation.
- To characterize the enzyme system involved in oxidative drug metabolism.
Main Methods:
- Aminopyrine oxidative demethylation as an assay for drug hydroxylation.
- Studied normal rats and phenobarbital-treated rats.
- Investigated the effects of TPN, carbon monoxide, and various reductase reactions.
Main Results:
- Optimal assay conditions for TPNH and aminopyrine concentrations were established.
- Drug hydroxylation was inhibited by carbon monoxide, unlike TPNH oxidase.
- Phenobarbital-treated rats showed increased TPNH-linked reductase activities and drug hydroxylation.
- A 1:1:1 stoichiometry of aminopyrine metabolism, TPNH oxidation, and formaldehyde formation was observed.
Conclusions:
- The drug-hydroxylating enzyme system involves microsomal TPNH-cytochrome c reductase and a CO-binding pigment.
- A reaction scheme for drug hydroxylation is proposed based on experimental data.
- Solubilization attempts of the enzyme system were presented.
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