title: Purification and partial characterization of squalene epoxidase from rat liver microsomes.
abstract: Squalene epoxidase (EC 1.14.99.7, squalene 2,3-monooxygenase (epoxidizing) was purified to an apparent homogeneity from rat liver microsomes. The purification was carried out by solubilization of microsomes by Triton X-100, fractionation with ion exchangers, hydroxyapatite, Cibacron Blue Sepharose 4B, and chromatofocusing column chromatography. A total purification of 143-fold over the first DEAE-cellulose fraction was achieved. The purified enzyme gave a single major band on SDS-polyacrylamide gel electrophoresis and the Mr was estimated to be 51 000 as a single polypeptide chain. The enzyme showed no distinct absorption spectrum in the visible regions. The squalene epoxidase activity was reconstituted with the purified enzyme, NADPH-cytochrome P-450 reductase (EC 1.6.2.4), FAD, NADPH and molecular oxygen in the presence of Triton X-100. The apparent Michaelis constants for squalene and FAD were 13 microM and 5 microM, respectively. The Vmax was about 186 nmol per mg protein per 30 min for 2,3-oxidosqualene. The enzyme activity was not inhibited by potent inhibitors of cytochrome P-450. It is suggested that squalene epoxidase is distinct from cytochrome P-450 isozymes.
mesh_terms: D000818:Animals; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D008970:Molecular Weight; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010105:Oxygenases / Q000302:isolation & purification* / Q000378:metabolism; D011335:Proadifen / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D050603:Squalene Monooxygenase
chemical_list: D011335:Proadifen; D010105:Oxygenases; D050603:Squalene Monooxygenase; D009251:NADPH-Ferrihemoprotein Reductase