Cyclization Of Squalene Research Articles

Nonoxidative cyclization of squalene by Tetrahymena pyriformis. Incorporation of a 3.beta. hydrogen (deuterium) atom into tetrahymanol

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNonoxidative cyclization of squalene by Tetrahymena pyriformis. Incorporation of a 3.beta. hydrogen (deuterium) atom into tetrahymanolD. John Aberhart and Eliahu CaspiCite this: J. Am. Chem. Soc. 1979, 101, 4, 1013–1019Publication Date (Print):February 1, 1979Publication History Published online1 May 2002Published inissue 1 February 1979https://doi.org/10.1021/ja00498a036RIGHTS & PERMISSIONSArticle Views93Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (884 KB) Get e-Alerts Get e-Alerts

Minor and trace sterols in marine invertebrates: VI. Occurrence and possible origins of sterols possessing unusually short hydrocarbon side chains

Sterols with biosynthetically unusually short side chains (fewer than eight carbon atoms expected for primary squalene cyclization products) have been identified in the extracts of numerous marine invertebrates. The structures of the short side chain and conventional side chain sterols have been determined for various species of Porifera and Coelenterata. Sterol structures were determined by comparison of their mass spectra and gas chromatographic retention times with those of authentic or synthetic samples. Evidence is presented supporting the natural occurrence of these compounds in the tissues of the marine invertebrates as opposed to formation by degradative processes during sample handling or laboratory work-up. The short side chain sterols were found to possess predominantly the androst-5-en-3β-ol nucleus with C-17 alkyl side chains ranging from zero to six carbon atoms. Concentrations of short side chain sterols range from trace levels to over 5% of the sterol mixture in various species. The possible origins of these short side chain sterols are evaluated in the light of current knowledge of sterol function, biosynthesis, dealkylation, microbial degradation, and autoxidation. Known sterol autoxidations are reviewed, and possible singlet oxygen and free radical mechanisms of sterol side chain autoxidation (at physiological temperatures) which may lead to sterols with shortened hydrocarbon side chain are suggested. The possible autoxidative generation of short side chain sterols from known marine sterols by the suggested mechanisms is evaluated through application of the REACT computer program. Predicted short side chains are tabulated for each parent marine sterol side chain and then compared with the compositions of the actual sterols found in the marine extracts examined. The possible natural environmental or in vivo autoxidative formation of the short side chain marine sterols is supported by these evaluations.

STEROL BIOSYNTHESIS BY STRAINS OFSACCHAROMYCES CEREVISIAEIN THE PRESENCE AND ABSENCE OF DISSOLVED OXYGEN

The content of sterols in Saccharomyces cerevisiae which has been harvested after anaerobic growth and then added to a complex nutrient medium, rises rapidly from ca. 1 mg/g dry yeast to ca. 10 mg in the presence of dissolved oxygen. A range of sterols, present principally as sterol esters, is formed during this period. The concentration of free sterols does not rise above 3 mg/g and esters are thought to form a reserve sterol pool. Cyclization of squalene to lanosterol in the presence of oxygen seems not to be markedly affected by oxygen concentration in contrast to demethylation and desaturation reactions on the pathway to ergosterol. When oxygen concentration falls to zero, further metabolism of preformed sterols continues, with the accumulation of episterol and ergosterol and reduction in the concentration of zymosterol and 24(28)-dehydroergosterol. During anaerobic growth a marked hydrolysis of sterol esters occurs and free sterols eventually predominate.

Nonoxidative cyclization of squalene by Tetrahymena pyriformis. The incorporation of a 3β-hydrogen (deuterium) atom into tetrahymanol

It was shown by 2H-n.m.r. spectroscopy that the proton introduced by T. pyriformis in the cyclization of squalene assumes the 3β-stereochemistry in the biosynthesized tetrahymanol.

Intracellular distribution and origin of pentacyclic triterpenes in Calendula officinalis leaves

In Calendula officinalis leaves the cyclization of squalene to β-amyrin and its further oxidation to oleanolic acid as well as the biosynthesis of all derivatives of oleanolic acid 3-glucoside and some derivatives of oleanolic acid 3-glucuronoside occur in the microsomal fraction. The final metabolites of oleanolic acid 3-glucoside series i.e. pentaglycosides, are translocated from this fraction, one to the cell wall and plasmalemma fraction and the other to the cytosol. The derivatives of oleanolic acid 3-glucoronoside are synthesized partially in other fractions and accumulate in the different membraneous structures of the cell.

In vitro cyclization of squalene 2,3-epoxide to α-amyrin by microsomes from bramble cell suspension cultures

Squalene 2,3-epoxide incubated with microsomes from bramble cell suspension cultures is shown to be converted into α-amyrin.

Biosynthesis of oleanene- and ursene-type triterpenes from [4-13C]mevalonic acid in tissue cultures of Isodon japonicus Hara

On the basis of the 13C-labelling patterns elucidated by 13C n.m.r. spectroscopy in oleanene- and ursene-type triterpenes (1)–(5) isolated from Isodon japonicus tissue cultures fed with [4-13C]mevalonic acid, Ruzicka's hypothesis for cyclisation of squalene 2,3-oxide to the pentacyclic triterpenes has been verified experi-mentally.

Mechanism of oxidative cyclization of squalene. Concerning the mode of formation on the 17(20) double bond in the biosynthesis of fusidic acid by Fusidium coccineum.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMechanism of oxidative cyclization of squalene. Mode of formation of the 17(20) double bond in the biosynthesis of fusidic acid by Fusidium coccineumRichard C. Ebersole, W. O. Godtfredson, S. Vangedal, and Eliahu CaspiCite this: J. Am. Chem. Soc. 1974, 96, 20, 6499–6507Publication Date (Print):October 1, 1974Publication History Published online1 May 2002Published inissue 1 October 1974https://doi.org/10.1021/ja00827a039RIGHTS & PERMISSIONSArticle Views131Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Microsomal synthesis of cholesterol from squalene, lanosterol, and desmosterol: Evidence for the presence of two noncatalytic activator proteins in the 105,000 g supernatant fraction from brain, heart, and kidney

The biosynthesis of C 27 sterols (used as a generic term for 3 β-hydroxysterols containing 27 carbon atoms) from squalene and lanosterol, of cholesterol from desmosterol, and of lanosterol from squalene by microsomal fractions from adult rat heart, kidney, and brain was investigated. These conversions required the presence of 105,000 g supernatant fraction. Heat treatment of the supernatant fractions resulted in a significant loss of their capacity to stimulate the conversion of squalene to sterols, but the capacity to stimulate conversion of lanosterol to C 27 sterols and desmosterol to cholesterol was unaffected. The stimulatory activity (for the conversion of all three substrates) of both the heated and unheated supernatant fractions was lost on treatment with trypsin. Thus the soluble fraction appears to contribute at least two essential protein components for the overall conversion of squalene to cholesterol; one a heat labile protein, which functions in the squalene to lanosterol sequence, and the other a heat-stable protein, which is operative in the pathway between lanosterol and cholesterol. Hepatic supernatant factors required for cholesterol synthesis by liver microsomal enzymes function with heart, kidney, and brain microsomal enzymes in stimulating sterol synthesis from squalene and sterol precursors. Moreover, heart, kidney, and brain supernatant fractions prepared in 100 m m phosphate buffer stimulated cholesterol synthesis from squalene and other sterol precursors by liver microsomes. The supernatant fractions of the extrahepatic tissues prepared in 20 m m phosphate buffer lacked the ability to stimulate the biosynthesis of lanosterol from squalene by liver microsomes but were able to stimulate the conversion of lanosterol to C 27 sterols or conversion of desmosterol to cholesterol. These findings indicate that the heat-stable protein factor present in the supernatant fractions from extrahepatic tissues is perhaps identical to that in liver, but that the heat-labile factor in extrahepatic tissues, which catalyzes the cyclization of squalene to lanosterol, differs in some respect from that in liver.

Model Calculations on the Squalene Cyclization

AbstractAs a model for the squalene cyclization the interaction between a methyl cation or a methyl radical and two double bonds has been studied using the CNDO/2 and INDO method. In both cases bond formation between the CH3‐group and one double bond is facilitated by a second one, but not in a concerted way.

Mechanism of oxidative cyclization of squalene. Evidence for cyclization of squalene from either end of the squalene molecule in the in vivo biosynthesis of fusidic acid by Fusidium coccineum.

Mechanism of oxidative cyclization of squalene. Evidence for cyclization of squalene from either end of the squalene molecule in the in vivo biosynthesis of fusidic acid by Fusidium coccineum.

Mechanism of squalene cyclization: The chiral origin of the C-7 and C-15 hydrogen atoms of fusidic acid

The C-2 protons of mevalonic acid are incorporated into C-7 and C-15 of fusidic acid with retention of their stereochemical integrity; this finding is in agreement with the accepted mode of squalene-oxide cyclization to the C-20 protosterol cation, and supports the proposed mechanisms for the enzymatic events at C-7 and C-15 in the biosynthesis of cholesterol in rat liver.

A Comparison of the effects of some hypocholesteremic compounds on squalene metabolism in Tetrahymena pyriformis and rat liver

1. 1. Six dialkylaminoethoxy compounds, five of which exhibit hypocholesteremic activity, have been compared for their effects on the growth of Tetrahymena pyriformis and on the in vitro cyclization of squalene to tetrahymanol by this organism. With one exception, there was good correlation between ability of the compounds to inhibit growth and squalene cyclization. There was also good correlation between inhibition of T. pyriformis squalene cyclase and hypocholesteremic activity. 2. 2. The above compounds have also been compared for their effects on the conversion of 2,3-oxidosqualene to C 30 and C 27, sterols by rat liver homogenate. Only two of the six (one of which did not display hypocholesteremic activity) inhibited this process at the concentrations employed. The effect of these two agents on the conversion of squalene to C 30 and C 27 sterols by rat liver homogenate was also examined. 3. 3. Cholesterol had no effect on either in vivo or in vitro squalene cyclization by T. pyriformis, nor did it overcome the in vitro inhibition of squalene cyclization by 3β-(β-dimethylaminoethoxy)-androst-5-en-17-one (DMAE-DHA). 4. 4. A lag period is associated with tetrahymanol synthesis by a cell-free preparation of T. pyriformis. Two fat-soluble antioxidants inhibited squalene cyclization by this preparation; one water-soluble one did not. Sulfhydryl-blocking agents had little effect on squalene cyclase activity.

TRITERPENOID BIOSYNTHESIS. THE STEREOSPECIFICITY IN THE ENZYMATIC CYCLIZATION OF SQUALENE TO β-AMYRIN

Abstract It was first proved that the 20α-methyl group, as well as the 4β-, 8-, 10-, 14-, and 17-methyls of β-amyrin biosynthesized from [6-D3-mevalonic acid in Pisum sativum are stereospecifically derived from the 3-methyl group of the acid. The result has substantiated the stereospecificity in the enzymatic cyclization of squalene to β-amyrin.

The effect of nicotinamide on the cholesterol biosynthesis by cell-free rat brain extract.

It has been reported that cell-free extracts of adult rat brain incubated with mevalonic acid-2-14C synthesize radioactive nonsaponifiable materials consisting largely of squalene, and the synthesis of digitonin-precipitable sterols from mevalonic acid is depressed by nicotinamide[1]. The evidence suggested that the cyclization of squalene was inhibited by nicotinamide. BOWEN et al.[2] reported that the cyclization of squalene in yeast was also inhibited by nicotinic acid. Serum cholesterol levels were reduced by nicotinic acid but not nicotinamide[3]. However, the mechanisms of this inhibition are not known. This paper reports the stimulation of formation of squalene from mevalonic acid in cell-free extracts in adult rat brain by nicotinamide. DL-Mevalonic acid-2-14C lactone (specific activity : 5.58 mCi/mM) was obtained from Daiichi Pure Chemicals Co., Ltd., and before use, lactone was converted to the acid by alkali. Squalene-14C (specific activity : 21.2 mCi/mM) used was prepared by rat liver enzyme according to the method of GOODMAN[4]. Male rats of Donryu strain weighing about 250 g were used. The rats were sacrificed by decapitation, and their brains were quickly excised. The brain homogenate and the components of incubation mixture were prepared according to the method of KELLEY et al. [1] except 0.1 μCi of mevalonic acid-14C or 0.05 μCi of squalene-14C as substrate was used. Incubation was carried out for 2 hours at 37°, and the reaction was stopped by the addition of 3.0 ml of water- ethanol (1:1) containing 15% KOH (w/v) and 20 μg each of carrier squalene and cholesterol, after which the mixture was heated for 1 hour at 90°. The mixture was added 6 ml of distilled water and extracted three times each time with 20 ml of petroleum ether. The combined petroleum ether was washed three times, each time with 20 ml of distilled water and evaporated to dryness. The dried nonsaponifiable extract obtained was dissolved in a small volume of benzene, and was applied on a silica gel plate for thin-layer chromatography. n-Hexene-ethyl acetate (9 :1) was used as an ascending solvent. After development, the plate was sprayed with 0.1 % 2, 7'-dichlorofluorescein ethanol solution to detect the carriers. The spots on the plate were determined by ultraviolet absorption. Then, the radioactive areas on the plate were determined using a thin-layer radiochromatogram scanner, and the radioactive products were scraped off and eluted from the gel by three washes with ethyl acetate. The ethyl acetate was transferred into a counting vial and dried under a stream of nitrogen. Radioactivity of each sample was assayed with a liquid scintillation counter. The results are summarized in Tables 1 and 2.The activity of the cell-free extracts of rat brain for the incorporation of mevalonic acid-2-14C into squalene-14C was markedly increased about 7 times by nictinamide. However, nicotinamide had no significant stimulatory effects on the formation of cholesterol-14C from squalene-14C.

魚類におけるスクワレンおよびコレステロールの生合成-II.

The biosynthesis of squalene and cholesterol from acetate-1-14C by the homogenate supernatant of carp hepatopancreas and from mevalonate-2-14C by that of rainbow trout liver was studied in vitro. The incubation was carried out with the addition of ATP, NAD, NADH, NADP and NADPH for four hours in the carp hepatopancreas preparation with acetate, and for two hours in the rainbow trout liver preparation with mevalonate under aerobic and anaerobic conditions at 30°C. The total radioactivities incorporated into the lipids of carp hepatopancreas preparations were less than 5% of the initial acetate, in which most of the label was found in the saponifiable fraction, whereas in the nonsaponifiable fraction the percentage radioactivities were not over 10%. Therefore, the net acetate incorporation into squalene and cholesterol does not exceed 0.5%. However, it was shown that the mevalonate incorporation by the rainbow trout liver preparation into such compounds was almost quantitative, if only one enantiomorph of DL-mevalonate were utilized on the pathway of cholesterogenesis. In general, the coenzyme requirements for cholesterol synthesis in the fish are not markedly different from those needed by land animals. As one of the cofactors required for the cyclization of squalene to lanosterol, molecular oxygen plays an important role as in the case of aerobic conditions. Moreover, the metabolic pathway from acetate or mevalonate via squalene to cholesterol and their relations as the precursor, intermediate and product are discussed.

Mechanism of squalene cyclization: the chiral origin of the C-22 hydrogen atoms of fusidic acid

The C-2 protons of mevalonic acid are incorporated with retention of configuration into C-22 of fusidic acid; this finding excludes the intermediacy of products with a Δ20(22) double bond in the formation of a Δ17(20) double bond in fusidic acid.

Dehydrogenation and dealkylation of various sterols byTetrahymena pyriformis

AbstractSterols are not found inTetrahymena pyriformis when this protozoan is grown in a medium free from exogenous sterols; instead, the principal solid alcohol that can be isolated from the organism is tetrahymanol. a pentacyclic triterpenoid alcohol with an unusual structure. The biosynthesis of tetrahymanol has been shown by appropriate labeling studies to involve a direct, nonoxidative, proton‐initiated cyclization of squalene rather than the more commonly found type of mechanism involving squalene 2,3‐oxide as an intermediate. In contrast, whenT. pyriformis is incubated with any one of a wide variety of added sterols, the biosynthesis of tetrahymanol is inhibited and the added sterol is accumulated by the organism and, in most cases, is converted metabolically into one or more other sterols. Four different types of transformation have been observed: the introduction of Δ5, Δ7 and Δ22 double bonds, and the removal of ethyl groups, but not methyl groups, from C‐24.

Biosynthesis of terpenes and steroids. Part III. Squalene cyclisation in the biosynthesis of triterpenoids; the biosynthesis of fern-9-ene in Polypodium vulgare Linn

An examination of the pentacyclic triterpenes of Polypodium vulgare Linn. has shown the presence of 21-epifern-9-ene, fern-7-ene, hopene-1, and an as yet unidentified triterpene hydrocarbon, in addition to the previously reported constituents. The biosynthesis of fern-9-ene was shown to involve a direct proton-catalysed cyclisation of squalene, rather than a cyclisation–reduction process based on 2,3-epoxysqualene.

Tetrahymanol Biosynthesis: STUDIES IN VITRO ON SQUALENE CYCLIZATION

Abstract The biosynthesis in vitro of tetrahymanol (II) from squalene (I) by enzyme preparations of the protozoan Tetrahymena pyriformis is described. The enzyme system involved has been obtained in a soluble, cell-free, lipid-free form, and remains active after freeze-drying. As with the live protozoa, the biosynthesis of tetrahymanol in vitro does not proceed via the intermediacy of 2,3-oxidosqualene; instead a nonoxidative, enzymatic cyclization of squalene occurs. This is an anaerobic process, and has been shown by isotopic labeling experiments with D2O and H218O to result in the acquisition of a hydrogen atom from the medium, presumably at C-3 of tetrahymanol and an oxygen atom from the medium at C-21 of tetrahymanol. The biogenetic implications of these findings are discussed.