scholarly journals The mechanism of the elaboration of ring b in ergosterol biosynthesis

1968 ◽  
Vol 108 (4) ◽  
pp. 527-531 ◽  
Author(s):  
M Akhtar ◽  
M. A. Parvez
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Double Bond ◽  
Ergosterol Biosynthesis ◽  
Hydrogen Atoms ◽  
Aerobic Conditions ◽  
Whole Cells ◽  
Dehydration Mechanism ◽  
Dehydrogenation Mechanism

Methods for the preparation of [3α−3H]ergosta-7,22-dien-3β-ol (5,6-dihydro-ergosterol), [5,6−3H2]ergosta-7,22-dien-3β-ol and [3α−3H]ergosta-7,22-diene-3β,5α-diol are described. It is shown that 5,6-dihydro[3α−3H]ergosterol on incubation under aerobic conditions with whole cells of Saccharomyces cerevisiae LK2G12 is efficiently converted into ergosterol. Studies carried out with dihydro[5α,6α−3H2]-ergosterol demonstrate that the introduction of the 5,6-double bond in ergosterol biosynthesis is attended by an overall cis-elimination of two hydrogen atoms. To differentiate between a hydroxylation–dehydration mechanism and a dehydrogenation mechanism, the metabolism of [3α−3H]ergosta-7,22-diene-3β,5α-diol was studied. It was shown that this diol is converted into ergosterol only under aerobic conditions. It is therefore suggested that the introduction of the 5,6-double bond of ergosterol does not occur through a hydroxylation–dehydration mechanism.

scholarly journals The introduction of the C-22–C-23 ethylenic linkage in ergosterol biosynthesis

1968 ◽  
Vol 106 (3) ◽  
pp. 623-626 ◽  
Author(s):  
M Akhtar ◽  
M. A. Parvez ◽  
P. F. Hunt
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Chemical Synthesis ◽  
Good Yield ◽  
The Other ◽  
Side Chain ◽  
Ergosterol Biosynthesis ◽  
Hydrogen Atoms ◽  
Whole Cells ◽  
C 23 ◽  
Methylene Derivative

Methods for the chemical synthesis of [23−3H2]lanosterol, [23,25−3H3]24-methyldihydrolanosterol and [24,28−3H2]24-methyldihydrolanosterol are described. It is shown that, in the biosynthesis of ergosterol from [26,27−14C2,23−3H2]lanosterol by the whole cells of Saccharomyces cerevisiae, one of the original C-23 hydrogen atoms is lost and the other is retained at C-23 of ergosterol. It is also shown that 24-methyldihydrolanosterol is converted into ergosterol in good yield and without prior conversion into a 24-methylene derivative. On the basis of these results possible pathways for the formation of the ergosterol side chain from a 24-methylene side chain are discussed.

scholarly journals The conversion of cholest-7-en-3β-ol into cholesterol. General comments on the mechanism of the introduction of double bonds in enzymic reactions

1967 ◽  
Vol 105 (3) ◽  
pp. 1187-1194 ◽  
Author(s):  
S. Marsh Dewhurst ◽  
M Akhtar
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Experimental Evidence ◽  
Double Bonds ◽  
Anaerobic Conditions ◽  
Hydrogen Atoms ◽  
Aerobic Conditions ◽  
Metabolic Studies ◽  
Hypothetical Mechanism ◽  
Dehydration Mechanism

Convenient syntheses of 6β-tritiated Δ7-cholestenol and 3α-tritiated Δ7-cholestene-3β,5α-diol are described. It was shown that the conversion of 6β-tritiated Δ7-cholestenol into cholesterol is accompanied by the complete retention of label. It was unambiguously established that the overall reaction leading to the introduction of the double bond in the 5,6-position in cholesterol occurs via a cis-elimination involving the 5α- and 6α-hydrogen atoms and that during this process the 6β-hydrogen atom remains completely undisturbed. Metabolic studies with 3α-tritiated Δ7-cholestene-3β,5α-diol revealed that under anaerobic conditions the compound is not converted into cholesterol. This observation, coupled with the previous work of Slaytor & Bloch (1965), is interpreted to exclude a hydroxylation–dehydration mechanism for the origin of the 5,6-double bond in cholesterol. It was also shown that under aerobic conditions 3α-tritiated Δ7-cholestene-3β,5α-diol is efficiently converted into cholesterol and that this conversion occurs through the intermediacy of 7-dehydrocholesterol. Cumulative experimental evidence presented in this paper and elsewhere is used to suggest that the 5,6-double bond in cholesterol originates through an oxygen-dependent dehydrogenation process and a hypothetical mechanism for this and related reactions is outlined.

Inhibition of Ergosterol Biosynthesis by Etaconazole in Ustilago maydis

1983 ◽  
Vol 38 (1-2) ◽  
pp. 28-34 ◽  
Author(s):  
Edith Ebert ◽  
John Gaudin ◽  
Wolfgang Muecke ◽  
Klaus Ramsteiner ◽  
Christian Vogel ◽  
...  
Keyword(s):  
Double Bond ◽  
Growth Phase ◽  
Ustilago Maydis ◽  
Ergosterol Biosynthesis ◽  
Triazole Fungicide ◽  
Dehydration Mechanism

The triazole fungicide etaconazole (CGA64 251) interferes with the ergosterol biosynthesis in Ustilago maydis by inhibiting the C-14 demethylation of the sterol nucleus. During the late log growth phase of U. maydis a novel endogenous sterol metabolite (14α-methyl-ergosta-8,24(28)- dien-3β,6α-diol) was discovered and analyzed, which accumulates under the influence of the fungicide. The structure of this metabolite points to a hydroxylation-dehydration mechanism for the introduction of the double bond at C-5 during the ergosterol biosynthesis.

scholarly journals Genomic Approach to Identification of Mutations Affecting Caspofungin Susceptibility in Saccharomyces cerevisiae

2004 ◽  
Vol 48 (10) ◽  
pp. 3871-3876 ◽  
Author(s):  
Sarit Markovich ◽  
Aya Yekutiel ◽  
Itamar Shalit ◽  
Yona Shadkchan ◽  
Nir Osherov
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Wall ◽  
Ergosterol Biosynthesis ◽  
Membrane Function ◽  
Minimum Effective Concentration ◽  
Fourfold Increase ◽  
Microdilution Method ◽  
New Genes ◽  
Broth Microdilution Method ◽  
Glucan Synthesis

ABSTRACT The antifungal agent caspofungin (CAS) specifically interferes with glucan synthesis and cell wall formation. To further study the cellular processes affected by CAS, we analyzed a Saccharomyces cerevisiae mutant collection (4,787 individual knockout mutations) to identify new genes affecting susceptibility to the drug. This collection was screened for increased CAS sensitivity (CAS-IS) or increased CAS resistance (CAS-IR). MICs were determined by the broth microdilution method. Disruption of 20 genes led to CAS-IS (four- to eightfold reductions in the MIC). Eleven of the 20 genes are involved in cell wall and membrane function, notably in the protein kinase C (PKC) integrity pathway (MID2, FKS1, SMI1, and BCK1), chitin and mannan biosynthesis (CHS3, CHS4, CHS7, and MNN10), and ergosterol biosynthesis (ERG5 and ERG6). Four of the 20 genes (TPO1, VPS65, VPS25, and CHC1) are involved in vacuole and transport functions, 3 of the 20 genes (CCR4, POP2, and NPL3) are involved in the control of transcription, and 2 of the 20 genes are of unknown function. Disruption of nine additional genes led to CAS-IR (a fourfold increase of MIC). Five of these nine genes (SLG1, ERG3, VRP1, CSG2, and CKA2) are involved in cell wall function and signal transduction, and two of the nine genes (VPS67 and SAC2) are involved in vacuole function. To assess the specificity of susceptibility to CAS, the MICs of amphotericin B, fluconazole, flucytosine, and calcofluor for the strains were tested. Seven of 20 CAS-IS strains (with disruption of FKS1, SMI1, BCK1, CHS4, ERG5, TPO1, and ILM1) and 1 of 9 CAS-IR strains (with disruption of SLG1) demonstrated selective susceptibility to CAS. To further explore the importance of PKC in CAS susceptibility, the activity of the PKC inhibitor staurosporine in combination with CAS was tested against eight Aspergillus clinical isolates by the microdilution assay. Synergistic or synergistic-to-additive activities were found against all eight isolates by use of both MIC and minimum effective concentration endpoints.

Characterization of squalene epoxidase activity from the dermatophyte Trichophyton rubrum and its inhibition by terbinafine and other antimycotic agents.

1996 ◽  
Vol 40 (2) ◽  
pp. 443-447 ◽  
Author(s):  
B Favre ◽  
N S Ryder
Keyword(s):  
Biochemical Characterization ◽  
Trichophyton Rubrum ◽  
Side Chain ◽  
Ergosterol Biosynthesis ◽  
Squalene Epoxidase ◽  
High Potency ◽  
Whole Cells ◽  
Absolute Requirement ◽  
Tertiary Amino

Squalene epoxidase (SE) is the primary target of the allylamine antimycotic agents terbinafine and naftifine and also of the thiocarbamates. Although all of these drugs are employed primarily in dermatological therapy, SE from dermatophyte fungi has not been previously investigated. We report here the biochemical characterization of SE activity from Trichophyton rubrum and the effects of terbinafine and other inhibitors. Microsomal SE activity from T. rubrum was not dependent on soluble cytoplasmic factors but had an absolute requirement for NADPH or NADH and was stimulated by flavin adenine dinucleotide. Kinetic analyses revealed that under optimal conditions the Km for squalene was 13 microM and its Vmax was 0.71 nmol/h/mg of protein. Terbinafine was the most potent inhibitor tested, with a 50% inhibitory concentration (IC50) of 15.8 nM. This inhibition was noncompetitive with regard to the substrate squalene. A structure-activity relationship study with some analogs of terbinafine indicated that the tertiary amino structure of terbinafine was crucial for its high potency, as well as the tert-alkyl side chain. Naftifine had a lower potency (IC50, 114.6 nM) than terbinafine. Inhibition was also demonstrated by the thiocarbamates tolciclate (IC50, 28.0 nM) and tolnaftate (IC50, 51.5 nM). Interestingly, the morpholine amorolfine also displayed a weak but significant effect (IC50, 30 microM). T. rubrum SE was only slightly more sensitive (approximately twofold) to terbinafine inhibition than was the Candida albicans enzyme. Therefore, this difference cannot fully explain the much higher susceptibility (> or = 100-fold) of dermatophytes than of yeasts to this drug. The sensitivity to terbinafine of ergosterol biosynthesis in whole cells of T. rubrum (IC50, 1.5 nM) is 10-fold higher than that of SE activity, suggesting that the drug accumulates in the fungus.

scholarly journals Combined Biosynthetic Pathway Engineering and Storage Pool Expansion for High-Level Production of Ergosterol in Industrial Saccharomyces cerevisiae

2021 ◽  
Vol 9 ◽  
Author(s):  
Zhi-Jiao Sun ◽  
Jia-Zhang Lian ◽  
Li Zhu ◽  
Yi-Qi Jiang ◽  
Guo-Si Li ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Biosynthetic Pathway ◽  
Metabolic Flux ◽  
Feeding Strategy ◽  
Pathway Engineering ◽  
Ergosterol Biosynthesis ◽  
Sterol Esters ◽  
Storage Pool ◽  
Ergosterol Content ◽  
Dry Cell Weight

Ergosterol, a terpenoid compound produced by fungi, is an economically important metabolite serving as the direct precursor of steroid drugs. Herein, ergsosterol biosynthetic pathway modification combined with storage capacity enhancement was proposed to synergistically improve the production of ergosterol in Saccharomyces cerevisiae. S. cerevisiae strain S1 accumulated the highest amount of ergosterol [7.8 mg/g dry cell weight (DCW)] among the wild-type yeast strains tested and was first selected as the host for subsequent metabolic engineering studies. Then, the push and pull of ergosterol biosynthesis were engineered to increase the metabolic flux, overexpression of the sterol acyltransferase gene ARE2 increased ergosterol content to 10 mg/g DCW and additional overexpression of a global regulatory factor allele (UPC2-1) increased the ergosterol content to 16.7 mg/g DCW. Furthermore, considering the hydrophobicity sterol esters and accumulation in lipid droplets, the fatty acid biosynthetic pathway was enhanced to expand the storage pool for ergosterol. Overexpression of ACC1 coding for the acetyl-CoA carboxylase increased ergosterol content from 16.7 to 20.7 mg/g DCW. To address growth inhibition resulted from premature accumulation of ergosterol, auto-inducible promoters were employed to dynamically control the expression of ARE2, UPC2-1, and ACC1. Consequently, better cell growth led to an increase of ergosterol content to 40.6 mg/g DCW, which is 4.2-fold higher than that of the starting strain. Finally, a two-stage feeding strategy was employed for high-density cell fermentation, with an ergosterol yield of 2986.7 mg/L and content of 29.5 mg/g DCW. This study provided an effective approach for the production of ergosterol and other related terpenoid molecules.

Photolyse du butène-1 dans l'ultraviolet à vide

1973 ◽  
Vol 51 (17) ◽  
pp. 2853-2859 ◽  
Author(s):  
Guy J. Collin
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Kinetic Energy ◽  
Thermal Energy ◽  
Hydrogen Atoms ◽  
Excited Molecules

The vacuum u.v. photolysis of 1 -butene was studied in the 147–105 nm region. The main products formed from the fragmentation of excited molecules are allene, 1,3-and 1,2-butadienes, ethylene, and acetylene. The addition of a hydrogen atom to the double bond produces mainly secondary butyl radicals (91%) at 147 nm. At 123.6 nm, this proportion becomes 82%. Thus at shorter wavelengths (10 and 11.6–11.8 eV), hydrogen atoms are produced with a kinetic energy higher than the thermal energy.

Cis-trans Isomerization in Polyisoprenes. Part VII. Double Bond Movement During Isomerization of Natural Rubber and Related Olefins

1967 ◽  
Vol 40 (3) ◽  
pp. 921-927
Author(s):  
J. I. Cunneen ◽  
G. M. C. Higgins ◽  
R. A. Wilkes
Keyword(s):  
Double Bond ◽  
Sulfur Dioxide ◽  
Natural Rubber ◽  
Structural Modification ◽  
Anaerobic Conditions ◽  
Aerobic Conditions ◽  
Trans Isomerization ◽  
Acidic Compounds

Abstract When trans-3-methyl-2-pentene or trans-3-methyl-3-hexene is treated with butadiene sulfone, thiolbenzoic acid, and dibenzoyl disulfide under anaerobic conditions, the olefin undergoes only cis-trans isomerization. However, similar reactions in the presence of oxygen or peroxides also cause changes in the position of the double bond. The latter structural modification is probably caused by acidic compounds formed by oxidation of the isomerization reagents. With natural rubber the nonrubber substances prevent movement of the double bond, and cis-trans isomerization is the sole change, even when the reaction with sulfur dioxide is carried out under aerobic conditions.

scholarly journals Transcriptomic Response of Saccharomyces cerevisiae during Fermentation under Oleic Acid and Ergosterol Depletion

Fermentation ◽  
2019 ◽  
Vol 5 (3) ◽  
pp. 57 ◽  
Author(s):  
Giacomo Zara ◽  
Hennie J. J. van Vuuren ◽  
Ilaria Mannazzu ◽  
Severino Zara ◽  
Marilena Budroni
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Oleic Acid ◽  
Lipid Fraction ◽  
Membrane Lipid ◽  
Ergosterol Biosynthesis ◽  
Methionine Biosynthesis ◽  
Transcriptomic Response ◽  
Hypoxic Conditions ◽  
Lipid Supplementation ◽  
Time Point

Under anaerobic/hypoxic conditions, Saccharomyces cerevisiae relies on external lipid supplements to modulate membrane lipid fraction in response to different stresses. Here, transcriptomic responses of two S. cerevisiae wine strains were evaluated during hypoxic fermentation of a synthetic must with/without ergosterol and oleic acid supplementation. In the absence of lipids, the two strains, namely EC1118 and M25, showed different behaviour, with M25 significantly decreasing its fermentation rate from the 72 h after inoculum. At this time point, the whole genome transcriptomic analysis revealed common and strain-specific responses to the lack of lipid supplementation. Common responses included the upregulation of the genes involved in ergosterol biosynthesis, as well as the seripauperin and the heat shock protein multigene families. In addition, the upregulation of the aerobic isoforms of genes involved in mitochondrial electron transport is compatible with the previously observed accumulation of reactive oxygen species in the two strains during growth in absence of lipids. Considering the strain-specific responses, M25 downregulated the transcription of genes involved in glucose transport, methionine biosynthesis and of those encoding mannoproteins required for adaptation to low temperatures and hypoxia. The identification of these pathways, which are presumably involved in yeast resistance to stresses, will assist industrial strain selection.

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