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RESEARCH PRODUCT

Evidence for Several Hepatic Proteins Related to Microsomal Epoxide Hydrolase

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Epoxide hydrolases catalyze the conversion of epoxides, some of which have been shown to be carcinogenic, to dihydrodiols (Guenthner and Oesch 1981). At least three forms of epoxide hydrolases exist in rats, two of which, namely mEHb and mEHch, are associated mainly with the microsomal fraction (Oesch et al 1984; Levin et al 1983) whereas one form namely cEH is found to a large extent in the cytosolic fraction (Gill and Hammock 1981). These three forms differ in their immunological and catalytic properties quite considerably (Guenthner et al 1981). In the case of mEHb the existence of several closely related isoenzymes with an identical apparent subunit molecular weight (Mrs) of 50,000 was suggested (Guengerich et al 1979; Guengerich et al 1979) based on the analysis of purified proteins. However a recent study (Falany et al 1987) implied that this finding could be an artefact due to the protein purification procedure. Several studies (Steinberg et al 1987; Galteau et al 1985) showed an apparent molecular weight of 50,000 in hepatocytes or liver. However during the studies for the presence of various epoxide hydrolase activities in hepatic endoplasmic reticulum and peroxisomes, in the latter, organelle proteins immunologically related to mEHb yet with molecular weights clearly distinct from the mEHb of the endoplasmic reticulum were found.