Evidence for a predominantly NADH-dependent O-dealkylating system in rat hepatic microsomes.
This study compared the NADH- and NADPH-supported p-nitrophenetole (NP) O-deethylase, ethylmorphine (EM) O-deethylase and EM N-demethylase activities of rat hepatic microsomes with respect to dioxygen requirement, inhibition by carbon monoxide, inhibition by classical inhibitors of cytochrome P-450 systems, and the involvement of NADH-cytochrome b5, cytochrome b5 reductase and NADPH-cytochrome P-450 reductase. The results generated the following conclusions and speculations: NADH- and NADPH-supported O-deethylations of NP involve different P-450 hemoproteins. This conclusion was based largely on the observations that the NADPH-supported reaction was inhibited by carbon monoxide and cyanide (5 mM), whereas the NADH-supported reaction was not; the NADH-supported reaction required a relatively high pO2 for maximal activity, whereas the NADPH-supported reaction did not, and the NADPH-supported reaction was depressed in microsomes from rats that had been administered Co2+, Mn2+, allylisopropylacetamide (AIA) or polyriboinosinic acid X polyribocytidylic acid (poly IC), whereas the NADH-supported reaction was not. However, the NADH- and NADPH-supported reactions shared some common features: both were strongly inhibited by alpha-naphthoflavone and weakly inhibited by 2-diethylaminoethyl 2,2-diphenyl valerate HCI (SKF 525-A), both were destroyed by linoleic acid hydroperoxide, and both were induced by 3-methylcholanthrene (MC) and phenobarbital. The use of antibodies against NADPH-cytochrome P-450 reductase, NADH-cytochrome b5 reductase and cytochrome b5 demonstrated that both the NADH- and the NADPH-supported reactions depend on established components of cytochrome P-450 systems. The P-450 hemoproteins involved primarily in both the NADH- and NADPH-supported deethylation of NP are the P1-450 type, i.e. they are markedly induced by MC and inhibited by alpha-napthoflavone. The NADH- and NADPH-supported O-deethylations of NP involve separate electron transfer systems.(ABSTRACT TRUNCATED AT 400 WORDS)
D000818:Animals; D000906:Antibodies / Q000276:immunology; D001571:Benzoflavones / Q000494:pharmacology; D002248:Carbon Monoxide / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D003486:Cyanides / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D003579:Cytochrome Reductases / Q000276:immunology / Q000502:physiology; D003573:Cytochrome b Group / Q000276:immunology / Q000502:physiology; D042966:Cytochrome-B(5) Reductase; D015786:Cytochromes b5; D003640:Dealkylation; D004579:Electron Transport; D005036:Ethylmorphine / Q000378:metabolism; D066298:In Vitro Techniques; D008041:Linoleic Acids / Q000494:pharmacology; D008054:Lipid Peroxides / Q000494:pharmacology; D008297:Male; D008345:Manganese / Q000494:pharmacology; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology*; D009243:NAD / Q000494:pharmacology*; D009249:NADP / Q000494:pharmacology; D009251:NADPH-Ferrihemoprotein Reductase / Q000502:physiology; D009578:Nitrobenzenes / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology; D010313:Partial Pressure; D010634:Phenobarbital / Q000494:pharmacology; D011335:Proadifen / Q000494:pharmacology; D051381:Rats
D000906:Antibodies; D001571:Benzoflavones; D003486:Cyanides; D003573:Cytochrome b Group; D008041:Linoleic Acids; D008054:Lipid Peroxides; D009578:Nitrobenzenes; D009243:NAD; C008285:linoleic acid hydroperoxide; D003035:Cobalt; D008345:Manganese; D009249:NADP; D008748:Methylcholanthrene; C011512:alpha-naphthoflavone; D002248:Carbon Monoxide; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D011335:Proadifen; D003579:Cytochrome Reductases; D042966:Cytochrome-B(5) Reductase; D009251:NADPH-Ferrihemoprotein Reductase; C013154:4-nitrophenetol; D005036:Ethylmorphine; D010100:Oxygen; D010634:Phenobarbital