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.
Highlights
Cytochrome P-45011 is immunochemically distinct from the major forms of hepatic cytochrome P-450 induced by phenobarbital or
The relatively high proportion of cytochrome P-4501 in the lung appears to be responsible for the higher rates of N-demethylation that have been observed in rabbit pulmonary as compared to hepatic microsomal fractions
AnalytLcal Procedures-Protein concentrations were measured by the method of Lowry et al [19], NADPH-dependent reduction of cytochrome c was determined by the method of Masters et al [20] as modified by Vermilion and Coon [21], cytochrome P-450 content by the method of Omura and Sato [22], flavin composition by the method of Faeder and Siegel [23]. and reduction of the flavin and subsequent oxidation with potassium ferricyanide according to the method of Masters et al [24]
Summary
P-450 reductases have identical physical, catalytic, and immunochemical properties. The relatively high proportion of cytochrome P-4501 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. Considerable progress has been made toward characterizing the rabbit pulmonary monooxygenase system It has been resolved into three components [5, 6], phospholipid, NADPH-cytochrome. P-450 reductase were elicited in goats and used to characterize immunochemically the rabbit pulmonary monooxygenase enzymes. The effects of the antibodies on the activity of reconstituted pulmonary monooxygenase systems and microsomal fractions were investigated and compared with results obtained using hepatic preparations. Spectral, immunochemical, and catalytic properties of pulmonary and hepatic NADPH-cytochrome.
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