title: Biosynthesis of 24,25-epoxycholesterol from squalene 2,3;22,23-dioxide.
abstract: [3H]Squalene 2,3(S);22(S),23-dioxide was prepared by incubation of [3H]mevalonate with S10 rat liver homogenate in the presence of 4,4,10 beta-trimethyl-trans-decal-3 beta-ol, a specific inhibitor of oxidosqualene cyclase (EC 5.4.99.7). Aerobic incubation of [3H]squalene 2,3(S);22(S),23-dioxide with S10 rat liver homogenate affords 24(S),25-epoxycholesterol with an efficiency comparable to that of the formation of cholesterol from squalene 2,3(S)-oxide. The product 24(S),25-epoxy-[3H]cholesterol was identified by reduction to 25-hydroxyl[3H]cholesterol and by benzoylation to 24(S),-25-epoxy[3H]cholesterol benzoate. Both the 25-hydroxy[3H]cholesterol and 24 (S),25-epoxy[3H]cholesterol benzoate were isotopically diluted and recrystallized to constant specific activity. Incubation of either [3H]squalene 2,3(S);22(S),23-dioxide or 24(S),25-epoxy[3H]cholesterol with S10 rat liver homogenate failed to produce any detectable 25-hydroxy[3H]cholesterol.
mesh_terms: D000332:Aerobiosis; D000818:Animals; D002784:Cholesterol / Q000031:analogs & derivatives* / Q000096:biosynthesis; D002855:Chromatography, Thin Layer; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D051381:Rats; D013185:Squalene / Q000031:analogs & derivatives* / Q000378:metabolism; D014316:Tritium
chemical_list: D014316:Tritium; C015171:2,3,22,23-dioxidosqualene; C028358:24,25-epoxycholesterol; D013185:Squalene; D002784:Cholesterol