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Methyl red azo-reductase and its induction by 3-methylcholanthrene in the liver by different species
Abstract:
1. Methyl red azo-reductase activity in the liver cytosol of mouse and sheep was considerably less than in the rat, guinea-pig, rabbit and hamster. In the mouse, the total activity of this soluble enzyme to reduce methyl red was only 4% of that found in rat. 2. Species variation in methyl red azo-reductase of microsomes was relatively small compared to that of the cytosol. 3. Azo-reductase in the cytosol of mouse liver also differed from that of the rat in its resistance to the inductive effects of 3-methylcholanthrene.
Insights
Mouse and sheep liver cytosol show significantly lower methyl red azo-reductase activity compared to other species. This enzyme
Area of Science:
- Biochemistry and Molecular Biology
- Pharmacology and Toxicology
- Comparative Physiology
Background:
- Methyl red azo-reductase is a key enzyme involved in xenobiotic metabolism.
- Understanding species-specific differences in enzyme activity is crucial for drug development and risk assessment.
- Previous studies have indicated variations in drug-metabolizing enzymes across species, but detailed comparisons for methyl red azo-reductase are limited.
Purpose of the Study:
- To investigate and compare the activity and inducibility of methyl red azo-reductase in the liver cytosol and microsomes across various species.
- To elucidate the species-specific differences in the metabolic pathways of methyl red.
- To assess the impact of 3-methylcholanthrene induction on mouse and rat liver azo-reductase activity.
Main Methods:
- Enzyme activity assays were performed on liver cytosol and microsomal fractions from mouse, sheep, rat, guinea-pig, rabbit, and hamster.
- Methyl red was used as the substrate to measure azo-reductase activity.
- The effect of 3-methylcholanthrene on enzyme activity was evaluated in mouse and rat liver preparations.
Main Results:
- Liver cytosol exhibited significant species variation in methyl red azo-reductase activity, with mouse and sheep showing considerably lower levels than rat, guinea-pig, rabbit, and hamster.
- Mouse liver cytosol displayed only 4% of the methyl red azo-reductase activity found in rat liver cytosol.
- Species variation in microsomal methyl red azo-reductase activity was less pronounced compared to the cytosol.
- Mouse liver cytosol azo-reductase demonstrated greater resistance to the inductive effects of 3-methylcholanthrene compared to rat liver azo-reductase.
Conclusions:
- Significant species-specific differences exist in mouse and sheep liver cytosolic methyl red azo-reductase activity, impacting xenobiotic metabolism.
- Microsomal azo-reductase activity shows less interspecies variability than cytosolic activity.
- The differential response of mouse and rat liver azo-reductase to 3-methylcholanthrene suggests distinct regulatory mechanisms and metabolic profiles.