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[Characteristics of 3,4-benzopyrene-induced cytochrome P-448 forms isolated from mouse liver microsomes]
Abstract:
Two cytochrome P-448 fractions, B1 and B2, were isolated from liver microsomes of 3,4-benzpyrene-induced inbred C57Bl/6 mice, using chromatography on octyl-Sepharose CL-4B and on Whatman 52E. During subsequent chromatography on hydroxylapatite fraction B1 was separated into 2 subfractions, G1 and G2. Cytochrome fractions B1, G1 and G2 have similar "peptide maps" differing from that of fraction B2. Cytochrome fraction B1 is immunologically identical to G2, partly to fraction B2 but is distinct from fraction G1. Fraction G2 is identified as the form of cytochrome P-448 catalyzing the hydroxylation of 3,4-benzpyrene and 7-ethoxyresorufin and existing in a low spin form. Cytochrome fraction G1 is apparently identical to the form P3-450. Fraction B2 was not yet described in current literature, since cytochrome P-448 (Mr = 53,000 Da) was identified only after the induction of mice with 3,4-benzpyrene but not with other inducers, e.g., polycyclic aromatic hydrocarbons.
Insights
Researchers isolated and characterized two cytochrome P-448 fractions (B1 and B2) from mouse liver microsomes. Fraction G2 was identified as the key enzyme for 3,4-benzpyrene hydroxylation.
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- Cytochrome P-450 enzymes are crucial for metabolizing xenobiotics.
- 3,4-benzpyrene is a model polycyclic aromatic hydrocarbon inducer of specific cytochrome P-450 forms.
- Understanding distinct cytochrome P-448 isoforms is vital for drug metabolism and toxicity studies.
Purpose of the Study:
- To isolate and characterize distinct cytochrome P-448 fractions from 3,4-benzpyrene-induced mouse liver microsomes.
- To identify the specific cytochrome P-448 isoform responsible for 3,4-benzpyrene hydroxylation.
- To differentiate between various cytochrome P-448 forms based on biochemical and immunological properties.
Main Methods:
- Isolation of cytochrome P-448 fractions using octyl-Sepharose CL-4B and Whatman 52E chromatography.
- Further separation of fractions using hydroxylapatite chromatography.
- Analysis of fractions using peptide mapping and immunological techniques.
Main Results:
- Two main cytochrome P-448 fractions, B1 and B2, were isolated.
- Fraction B1 was further separated into G1 and G2 subfractions.
- Fraction G2, identified as cytochrome P-448, catalyzes 3,4-benzpyrene and 7-ethoxyresorufin hydroxylation and exists in a low spin form.
- Fraction G1 is similar to P3-450, and fraction B2 represents a novel, previously undescribed form.
Conclusions:
- Cytochrome P-448 fraction G2 is the primary enzyme responsible for 3,4-benzpyrene hydroxylation in induced mice.
- Distinct cytochrome P-448 isoforms (G1, G2, B2) possess unique biochemical and immunological characteristics.
- The characterization of these fractions advances the understanding of xenobiotic metabolism and enzyme specificity.