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Cytochrome P-450 isozyme LM3b from rabbit liver microsomes. Induction by triacetyloleandomycin purification and
Abstract:
Oral administration of triacetyloleandomycin (TAO), 1 mmol/kg/day for 7 days to mature male New Zealand White rabbit results in a significant increase in the content of liver microsomal cytochrome P-450. This increase is accompanied by the occurrence on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the microsomes of a strong band in the zone of electrophoretic mobility associated with the LM3 isozymes and the stimulation of a number of monooxygenase activities of these microsomes including aminopyrine, chlorcyclizine, TAO, and erythromycin demethylation as well as 2-OH-estradiol and 6 beta OH-testosterone hydroxylation. Cytochrome P-450 LM3 (TAO) from these liver microsomes, purified to electrophoretic homogeneity, had Mr = 52,000 as determined by calibrated sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Comparison with isozymes LM3a, LM3b, and LM3c isolated from control animals, by a number of criteria including spectral data, amino acid content, NH2-terminal sequence analysis, peptide mapping, immunological properties, and monooxygenase activities of reconstituted system, indicated that isozymes LM3 (TAO) and LM3b are very similar, if not identical, proteins. We conclude that TAO must be considered as a new type of inducer of microsomal cytochrome P-450 from rabbit liver.
Insights
Triacetyl-oleandomycin (TAO) administration significantly increases liver microsomal cytochrome P-450 in rabbits. This indicates TAO is a novel inducer of this crucial enzyme system.
Area of Science:
- Biochemistry
- Pharmacology
- Enzymology
Background:
- Cytochrome P-450 enzymes are critical for drug metabolism.
- Understanding enzyme induction is vital for drug development and safety.
Purpose of the Study:
- To investigate the effect of triacetyl-oleandomycin (TAO) on liver microsomal cytochrome P-450 in rabbits.
- To characterize the specific cytochrome P-450 isozymes induced by TAO.
Main Methods:
- Oral administration of TAO to male New Zealand White rabbits.
- Analysis of liver microsomes using SDS-PAGE and enzyme activity assays.
- Purification and characterization of induced cytochrome P-450 isozymes.
Main Results:
- TAO significantly increased liver microsomal cytochrome P-450 content.
- SDS-PAGE revealed a prominent band associated with LM3 isozymes.
- Induced microsomes showed enhanced demethylation and hydroxylation activities.
- Purified Cytochrome P-450 LM3 (TAO) was found to be nearly identical to LM3b.
Conclusions:
- Triacetyl-oleandomycin (TAO) acts as a novel inducer of rabbit liver microsomal cytochrome P-450.
- The LM3 isozyme family is a primary target for TAO-mediated induction.
- TAO's induction profile suggests potential interactions with other xenobiotics metabolized by LM3.