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The rabbit pulmonary monooxygenase system. Immunochemical and biochemical characterization of enzyme components
Abstract:
The enzymatic components of the rabbit pulmonary monooxygenase system, cytochromes P-450I and P-450II and NADPH-cytochrome P-450 reductase, are immunochemically distinct proteins. In pulmonary microsomes, the N-demethylation of benzphetamine, amino-pyrine, and ethylmorphine, and the O-deethylation of 7-ethoxycoumarin are dependent only on cytochrome P-450I, and the hydroxylation of coumarin is apparently catalyzed by both cytochromes. Cytochrome P-450II is immunochemically distinct from the major forms of hepatic cytochrome P-450 induced by phenobarbital or 3-methylcholanthrene, whereas cytochrome P-450I is indistinguishable from the former on the basis of physical and catalytic as well as immunochemical characteristics. Pulmonary and hepatic NADPH-cytochrome P-450 reductases also have identical physical, catalytic, and immunochemical properties. The lack of response of the lung monooxygenase system to phenobarbital, therefore, is apparently not due to an inability of the lung to synthesize the enzymes induced by phenobarbital in the liver. The relatively high proportion of cytochrome P-450I in the lung appears to be responsible for the higher rates (per nmol of P-450) of N-demethylation that have been observed in rabbit pulmonary as compared to hepatic microsomal fractions.
Insights
Rabbit lungs contain distinct cytochrome P-450 enzymes (P-450I and P-450II) responsible for drug metabolism. Cytochrome P-450I drives N-demethylation and O-deethylation, explaining higher lung metabolic rates compared to the liver.
Area of Science:
- Biochemistry
- Pharmacology
- Pulmonary Medicine
Background:
- The pulmonary monooxygenase system, crucial for drug metabolism, involves cytochromes P-450 and NADPH-cytochrome P-450 reductase.
- Understanding the specific roles and characteristics of pulmonary cytochromes P-450 is essential for comprehending lung drug metabolism.
Purpose of the Study:
- To immunochemically characterize the enzymatic components of the rabbit pulmonary monooxygenase system.
- To determine the substrate specificity and catalytic roles of pulmonary cytochromes P-450I and P-450II.
- To compare pulmonary and hepatic cytochrome P-450 systems.
Main Methods:
- Immunochemical analysis to distinguish between pulmonary and hepatic cytochrome P-450 proteins.
- Enzymatic assays to assess N-demethylation, O-deethylation, and hydroxylation activities.
- Comparison of physical, catalytic, and immunochemical properties of pulmonary and hepatic enzymes.
Main Results:
- Pulmonary cytochromes P-450I and P-450II are immunochemically distinct.
- Cytochrome P-450I is primarily responsible for N-demethylation and O-deethylation of specific substrates in lung microsomes.
- Pulmonary cytochrome P-450I is indistinguishable from phenobarbital-induced hepatic cytochrome P-450, while P-450II is distinct.
- Pulmonary and hepatic NADPH-cytochrome P-450 reductases share identical properties.
- Higher N-demethylation rates in lung microsomes are attributed to a greater proportion of cytochrome P-450I.
Conclusions:
- The rabbit lung monooxygenase system possesses unique enzymatic profiles compared to the liver.
- Cytochrome P-450I plays a significant role in the metabolic capacity of the rabbit lung.
- The observed differences in metabolic activity are linked to the specific composition of cytochrome P-450 isoforms in the lung.