title: Regulation of ergosterol biosynthesis and sterol uptake in a sterol-auxotrophic yeast.
abstract: Inhibition of sterol uptake in Saccharomyces cerevisiae sterol auxotroph FY3 (alpha hem1 erg7 ura) by delta-aminolevulinic acid (ALA) is dependent on the ability of the organism to synthesize heme from ALA. Sterol-depleted cells not exposed to ALA or strain PFY3 cells, with a double heme mutation, exposed to ALA did not exhibit inhibition of sterol uptake. Addition of ALA to sterol-depleted FY3 stimulated production of a high endogenous concentration of 2,3-oxidosqualene (25.55 micrograms mg-1 [dry weight]) at 24 h, whereas FY3 not exposed to ALA or PFY3 exposed to ALA did not accumulate 2,3-oxidosqualene. The high concentration of 2,3-oxidosqualene in FY3 with ALA decreased, and 2,3;22,23-dioxidosqualene increased to a very high level. The elevation of 2,3-oxidosqualene by ALA was correlated with a fivefold increase in the activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (EC 1.1.1.34). The enhanced activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase was prevented by cycloheximide but not chloramphenicol and was dependent on a fermentative energy source. Inhibition of sterol uptake could not be attributed to 2,3-oxidosqualene or 2,3;22,23-dioxidosqualene but was due to a nonsaturating level of ergosterol produced as a consequence of heme competency through a leaky erg7 mutation.
authors.forename: R T
authors.initials: RT
authors.lastname: Lorenz
authors.forename: L W
authors.initials: LW
authors.lastname: Parks
mesh_terms: D000622:Aminolevulinic Acid / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002784:Cholesterol / Q000378:metabolism; D004875:Ergosterol / Q000096:biosynthesis*; D006418:Heme / Q000378:metabolism; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D008055:Lipids / Q000032:analysis; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000032:analysis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D013185:Squalene / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D013261:Sterols / Q000378:metabolism*
chemical_list: C002821:2,3-oxidosqualene; D008055:Lipids; D013261:Sterols; C015171:2,3,22,23-dioxidosqualene; D006418:Heme; D013185:Squalene; D000622:Aminolevulinic Acid; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D004875:Ergosterol