Regulation of squalene epoxidase activity was examined in rat hepatic microsomes. The hepatic squalene epoxidase activity was high in the dark period and low in the light period. Three percent cholestyramine feeding increased the hepatic squalene epoxidase activity by 2.5-fold, and the administration of lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, incre...

Squalene epoxidase (Erg1p) is an essential enzyme in the ergosterol biosynthesis pathway in yeast. For its enzymatic activity, Erg1p requires molecular oxygen, NAD(P)H and FAD. Amino acid analysis and sequence alignment with other squalene epoxidases revealed two highly conserved FAD-binding domains, FAD I and FAD II. By random PCR mutagenesis of the ERG1 gene, one erg1 allele was isolated that...

Regulation of squalene epoxidase in the cholesterol biosynthetic pathway was studied in a human hepatoma cell line, HepG2 cells. Since the squalene epoxidase activity in cell homogenates was found to be stimulated by the addition of Triton X-100, enzyme activity was determined in the presence of this detergent. Incubation of HepG2 cells for 18 h with L-654,969, a potent competitive inhibitor of...

Squalene epoxidase activity has been studied in cell-free preparations of Chinese hamster ovary (CHO) cells and rat liver. In contrast to rat liver microsomal squalene epoxidase, the enzyme of CHO cells is only slightly activated by the autologous cytosolic fraction, whereas phosphatidylglycerol or rat liver cytosolic preparations are potent stimulators of this enzyme. Triton X-100, a known sti...

We investigated the biochemical basis for resistance in six sequential clinical isolates of Trichophyton rubrum, from the same patient, which exhibited high-level primary resistance to terbinafine. Cellular ergosterol biosynthesis was measured by incorporation of [14C]acetate, and microsomal squalene epoxidase was assayed by conversion of [3H]squalene to squalene epoxide and lanosterol. Direct ...

Squalene epoxidase, encoded by the ERG1 gene in yeast, is a key enzyme of sterol biosynthesis. Analysis of subcellular fractions revealed that squalene epoxidase was present in the microsomal fraction (30,000 x g) and also cofractionated with lipid particles. A dual localization of Erg1p was confirmed by immunofluorescence microscopy. On the basis of the distribution of marker proteins, 62% of ...

Rat liver microsomes previously heated to 50” for 5 mm accumulate 2,3-oxidosqualene on incubation with squalene. Squalene epoxidase activity can be assayed either with squalene and heated microsomes or with lO,ll-dihydrosqualene and intact microsomes. In common with other monooxygenases, the epoxidase requires TPNH and molecular oxygen. Both a soluble fraction of rat liver and microsomes are ne...

Rat liver microsomes previously heated to 50” for 5 mm accumulate 2,3-oxidosqualene on incubation with squalene. Squalene epoxidase activity can be assayed either with squalene and heated microsomes or with lO,ll-dihydrosqualene and intact microsomes. In common with other monooxygenases, the epoxidase requires TPNH and molecular oxygen. Both a soluble fraction of rat liver and microsomes are ne...

Squalene epoxidase enzymes catalyse the conversion of squalene into 2,3-oxidosqualene, the precursor of cyclic triterpenoids. Here we report that the Arabidopsis drought hypersensitive/squalene epoxidase 1-5 (dry2/sqe1-5) mutant, identified by its extreme hypersensitivity to drought stress, has altered stomatal responses and root defects because of a point mutation in the SQUALENE EPOXIDASE 1 (...

Sterol biosynthesis by prokaryotic organisms is very rare. Squalene epoxidase and lanosterol synthase are prerequisite to cyclic sterol biosynthesis. These two enzymes, from the methanotrophic bacterium Methylococcus capsulatus, were functionally expressed in Escherichia coli. Structural analyses of the enzymatic products indicated that the reactions proceeded in a complete regio- and stereospe...