Lung cytochrome P450-dependent benzyloxyphenoxazone debenzylase and ethoxyphenoxazone deethylase activities in total microsomal and isolated alveolar type II cells: responses to changes in assay conditions with special reference to non-linear dependence at low enzyme concentration.
1. Responses of cytochrome P450-dependent ethoxyphenoxazone deethylase (EtOPx'ase) and benzyloxyphenoxazone debenzylase (BzOPx'ase) activities to changes in assay conditions were measured in total microsomal and isolated alveolar type II (tII) cells from rats pretreated with beta-naphthoflavone. 2. Whereas microsomal EtOPx'ase activity was unaffected by storage at -80 degrees C for up to 4 months, BzOPx'ase activity began to decline after only 1 month. 3. The microsomal and type II activities were unaffected by changes in pH (7.2-8.0) or salt content. 4. The type II activities increased after sonication 2.3-2.7-fold or in the presence of 10 microM dicumarol 1.7-1.9-fold. 5. Type II BzOPx'ase was sensitive to metyrapone (MP) whereas EtOPx'ase was sensitive to alpha-naphthoflavone (ANF). I50 values for the tII activities were calculated as: 0.63 microM--MP (BzOPx'ase), 80 microM--MP (EtOPx'ase), 0.024 microM--ANF (EtOPx'ase). At the highest concentration of ANF (10 microM), 50% inhibition tII BzOPx'ase was not observed. The results were similar to those obtained with the total lung microsomal fraction. 6. Microsomal and tII BzOPx'ase activities exhibited non-linear dependence at low enzyme concentration. Linearity was restored by 0.5 mM dimyristoylphosphatidylcholine.
California State Department of Health Services, Sacramento 95814.
J
J
Rabovsky
D J
DJ
Judy
M
M
Goddard
W H
WH
Pailes
V
V
Castranova
D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D001728:Dicumarol / Q000494:pharmacology; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008168:Lung / Q000201:enzymology*; D008297:Male; D008797:Metyrapone / Q000494:pharmacology; D008861:Microsomes / Q000201:enzymology*; D010088:Oxidoreductases / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000166:cytology / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000494:pharmacology; D013010:Sonication; D013395:Sucrose / Q000494:pharmacology
D001571:Benzoflavones; D012965:Sodium Chloride; D013395:Sucrose; C011512:alpha-naphthoflavone; D001728:Dicumarol; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; C063849:benzyloxyphenoxazone debenzylase; D019363:Cytochrome P-450 CYP1A1; D008797:Metyrapone