title: The effect of carbon monoxide on the nature of the accumulated 4,4-dimethyl sterol precursors of cholesterol during its biosynthesis from (2-14C)mevalonic acid in vitro.
abstract: Cholesterol biosynthesis was studied in rat liver subcellular fractions incubated with dl-[2-(14)C]mevalonic acid under gas phases consisting of either N(2)+O(2) (90:10) or CO+O(2) (90:10). CO inhibits cholesterol biosynthesis from [2-(14)C]mevalonic acid and results in a large accumulation of radioactive 4,4-dimethyl sterols. Separation of the components of the 4,4-dimethyl sterol fraction showed that lanosterol and dihydrolanosterol are the major components that accumulate during cholesterol biosynthesis in an atmosphere containing CO, whereas 14-demethyl-lanosterol and 14-demethyldihydrolanosterol are the major components of the much less intensely radioactive 4,4-dimethyl sterol fraction isolated from incubations with N(2)+O(2) as the gas phase. The identities of lanosterol, dihydrolanosterol and 14-demethyldihydrolanosterol were confirmed by both radiochemical and physicochemical methods, including g.l.c. and combined g.l.c.-mass spectrometry. CO therefore results in a qualitative as well as a quantitative difference in the 4,4-dimethyl sterol fraction which arises during cholesterol biosynthesis from mevalonic acid. The specific radioactivity of the [(14)C]lanosterol biosynthesized in the presence of CO was lower than that of its companion, [(14)C]dihydrolanosterol. The relative amounts of 4,4-dimethyl-Delta(24)-sterols and 4,4-dimethyl-24,25-dihydrosterols present in each type of incubation suggest that enzymic reduction of the sterol side chain occurs predominantly at a stage after that of lanosterol.
mesh_terms: D000818:Animals; D001345:Autoradiography; D002247:Carbon Isotopes; D002248:Carbon Monoxide / Q000494:pharmacology*; D002784:Cholesterol / Q000096:biosynthesis*; D002849:Chromatography, Gas; D002855:Chromatography, Thin Layer; D066298:In Vitro Techniques; D007810:Lanosterol / Q000096:biosynthesis; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D008798:Mevalonic Acid / Q000378:metabolism*; D051381:Rats; D013056:Spectrophotometry, Ultraviolet; D013261:Sterols / Q000096:biosynthesis* / Q000138:chemical synthesis; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D013261:Sterols; D007810:Lanosterol; D002248:Carbon Monoxide; D002784:Cholesterol; D008798:Mevalonic Acid