DISTRIBUTION OF POLYCYCLIC-HYDROCARBON METABOLISM-LINKED ENZYMES IN SPECIALIZED REGIONS OF THE ENDOPLASMIC-RETICULUM

Microsomal enzymes were partially separated by centrifugation in continuous sucrose gradients containing a low concentration of detergent into four bands in which the following enzymes were enriched: (I) glucose-6-phosphatase (d-glucose-6-phosphate phosphohydrolase, EC 3.1.3.9); (II) cytochrome P-450, NADPH-cytochrome c reductase (NADPH:ferricytochrome oxidoreductase, EC 1.6.2.4), monooxygenase (7-ethoxycoumarin-O-deethylase); (III) cytochrome b5, NADH cytochrome c reductase (NADH:ferricytochrome oxidoreductase, EC 1.6.2.2), epoxide hydratase (glycol hydro-lyase (epoxide-forming), EC 4.2.1.63), and UDPglucuronyltransferase (UDPglucoronate β-glucuronosyltransferase (acceptor-unspecific), EC 2.4.1.17); (IV) glutathione-S-transferases (RX:glutathione R-transferase, EC 2.5.1.18). The distribution of epoxide hydratase in the active fractions was identical whether determined with styrene oxide or benzo(a)pyrene-4,5-oxide as substrate giving further support to the conclusion that both substrates are hydrated by the same enzyme. The fact that epoxide hydratase, UDPglucuronyltransferase and microsomal glutathione-S-transferase activities were not enriched in the same fractions as the cytochrome P-450 monooxygenase system argues against a firm spatial association of the bulk of any of the former enzymes with the bulk of the monooxygenases system, although they catalyze consecutive reactions. Inclusion of antibodies to epoxide hydratase in the sucrose gradients inhibited the epoxide hydratase activity but did not affect monooxygenase activity which again suggests spatial independence of these enzymes. © 1979.