Diethyl ether as a substrate for acetone/ethanol-inducible cytochrome P-450 and as an inducer for cytochrome(s) P-450.
The ability of diethyl ether to serve as a substrate for microsomal and purified cytochrome P-450 (P-450) and as an inducer for rat hepatic microsomal monooxygenase activities was examined. Microsomal oxidation of ether to acetaldehyde, as monitored by high pressure liquid chromatography, was elevated 3- to 5-fold by treatment of rats with acetone or ethanol, 1.5- to 2-fold by treatment with ether, and only slightly by phenobarbital treatment. Ether also induced N-nitrosodimethylamine demethylase by up to 2-fold and 7-pentoxyresorufin dealkylation by up to 10-fold. These trends agreed with immunoblot experiments in which ether was a weak inducer of the P-450 isozyme IIE1 (encoded by the rat gene P450IIE1), but a stronger inducer of IIB1. A monoclonal antibody against IIE1 inhibited the deethylation by 78% in microsomes from acetone-treated rats and by 45% in controls. N-Nitrosodimethylamine, as well as common inhibitors of IIE1 such as hexane, benzene, pyrazole, and phenylethylamine, strongly inhibited ether deethylation. Using microsomes from acetone-induced rats, the apparent Km for deethylation was 13.4 +/- 2.4 microM and the Vmax was 8.2 +/- 0.2 (nmol of acetaldehyde/min/nmol of P-450). The Km for the controls was 71.3 +/- 9.5 microM. The rates of deethylation at 1 mM ether by purified, reconstituted IIE1 and IIB1 were 4.2 and 0.42 (nmol of acetaldehyde/min/nmol of P-450), respectively. Cytochrome b5 stimulated the rate due to IIE1 apparently by a decrease in the Km. These findings, along with previous work showing marked inhibition by ether of IIE1-dependent reactions, strongly support a major role for this isozyme in ether metabolism.
Brady
J F
JF
Department of Biochemistry, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark 07103.
Lee
M J
MJ
Li
M
M
Ishizaki
H
H
Yang
C S
CS
D000096:Acetone / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D019392:Cytochrome P-450 CYP2E1; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000502:physiology; D004790:Enzyme Induction; D000431:Ethanol / Q000494:pharmacology; D004986:Ether / Q000378:metabolism* / Q000494:pharmacology; D005019:Ethyl Ethers / Q000378:metabolism*; D007530:Isoflurane / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010084:Oxidation-Reduction; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors; D051381:Rats; D011919:Rats, Inbred Strains
D000911:Antibodies, Monoclonal; D005019:Ethyl Ethers; D004986:Ether; D000096:Acetone; D000431:Ethanol; D003577:Cytochrome P-450 Enzyme System; D007530:Isoflurane; D019392:Cytochrome P-450 CYP2E1; D010089:Oxidoreductases, N-Demethylating