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© 1985 Oxford University Press

research-article

Interaction of Trichloroethane Isomers with Cytochrome P-450 in the Perfused Rat Liver

TAKEHITO TAKANO, YOSHIFUMI MIYAZAKI and YUTAKA MOTOHASHI

Department of Hygiene, School of Medicine, Tokyo Medical and Dental University Tokyo 113, Japan

Interaction of Trichloroethane Isomers with Cytochrome P-450 in the Perfused Rat Liver. TAKANO, T., MIYAZAKI, Y., and MOTOHASHI, Y. (1985). Fundam. Appl. Toxicol. 5, 353–360. The real-time interactions of 1,1,1-trichloroethane (TCE) and 1,1,2-TCE with cytochrome P-450 were observed using in vivo optical methods to measure the spectral changes of cytochrome P-450 and the reduction-oxidation transition of pyridine nucleotides in the perfused liver of rats treated with phenobarbital. Changes in oxygen consumption and TCE uptake were also measured. The spectral changes of cytochrome P-450 indicated that both TCE isomers bound to low spin (substrate free) ferric cytochrome P-450 and formed a high spin (substrate complexed) form. However, 1,1,1-TCE bound more tightly to cytochrome P450 and seemed to be only slowly metabolized compared to 1,1,2-TCE. The stoichiometry of the change in oxygen consumption rate to the change in 1,1,1-TCE uptake rate ranged between 5/1, and 9/1, whereas that of 1,1,2-TCE was 1.4 to 2.0. Decreases in reduced pyridine nucleotides associated with TCE administration were significantly larger with 1,1,1-TCE than with 1,1,2-TCE. The inhibitory effect of 1,1,1-TCE on hexobarbital metabolism in the perfused liver was greater than that of 1,1,2-TCE. Considering our previous data indicating that TCE did not stimulate mitochondrial respiration, it is postulated that the far higher amount of oxygen consumption associated with the binding of 1,1,1-TCE to cytochrome P450 than the amount which was necessary to mixed-function oxidation of this compound was due to an uncoupling effect of 1,1,1 -TCE on the mixed-function oxidase system.


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