Showing papers on "Lanosterol published in 1977"
TL;DR: Tetrad analysis showed that the pleiotropic properties of each of the mutants resulted from a single mutation in one of five unlinked loci affecting heme biosynthesis, and each mutation resulted in loss of a single enzyme activity.
217 citations
TL;DR: In this article, the effects of cholesterol, 4,4-dimethylcholesterol, and lanosterol (4,4',14alpha-trimethyl-delta8,24-cholestadiene-3beta-ol) on lecithin vesicles have been compared.
Abstract: The effects of cholesterol, 4,4-dimethylcholesterol, and lanosterol (4,4',14alpha-trimethyl-delta8,24-cholestadiene-3beta-ol) on some properties of lecithin vesicles have been compared. Unlike cholesterol, lanosterol retards the exit of trapped glucose from phospholipid vesicles only slightly. The 13C nuclear magnetic resonance spectrum of cholesterol/lecithin vesicles shows no resonances attributable to the sterol. By contrast, several resonances attributable to quaternary carbon atoms or methyl groups are seen in the 13C nuclear magnetic resonance spectrum of lanosterol/lecithin vesicles, indicating that lanosterol is much less immobilized than cholesterol. Because the membrane behavior of 4,4-dimethylcholesterol is closely similar to that of cholesterol, it is concluded that the axial 14-alpha-methyl group is responsible for the lessened membrane immobilization of lanosterol. The results emphasize the importance of a planar sterol alpha-face for interaction with phospholipid acyl chains.
99 citations
01 Nov 1977
TL;DR: It is concluded that the axial 14-alpha-methyl group is responsible for the lessened membrane immobilization of lanosterol, and emphasizes the importance of a planar sterol alpha-face for interaction with phospholipid acyl chains.
Abstract: The effects of cholesterol, 4,4-dimethylcholesterol, and lanosterol (4,4',14α-trimethyl-δ 8,24 -cholestadiene-3β-ol) on some properties of lecithin vesicles have been compared. Unlike cholesterol, lanosterol retards the exit of trapped glucose from phospholipid vesicles only slightly. The 13 C nuclear magnetic resonance spectrum of cholesterol/lecithin vesicles shows no resonances attributable to the sterol. By contrast, several resonances attributable to quaternary carbon atoms or methyl groups are seen in the 13 C nuclear magnetic resonance spectrum of lanosterol/lecithin vesicles, indicating that lanosterol is much less immobilized than cholesterol. Because the membrane behavior of 4,4-dimethylcholesterol is closely similar to that of cholesterol, it is concluded that the axial 14-α-methyl group is responsible for the lessened membrane immobilization of lanosterol. The results emphasize the importance of a planar sterol α-face for interaction with phospholipid acyl chains.
94 citations
TL;DR: The highly unsaturated fatty acids, arachidonate and linoleate, were specific inhibitors of 3-hydroxy-3-methyl-glutaryl-CoA synthase and ricinoleate and phytanate diminished the conversion of mevalonate to sterols by inhibiting a step or steps between squalene and lanosterol.
85 citations
TL;DR: Sterols of a nystatin resistant mutant of the wild type parent of Saccharomyces cerevisiae were separated by a newly developed procedure involving high-pressure liquid chromatography and were identified and indicated a block in removal of the methyl group at C-14 of lanosterol.
Abstract: Sterols of a nystatin resistant mutant of the wild type parent of Saccharomyces cerevisiae were separated by a newly developed procedure involving high-pressure liquid chromatography and were identified. The mutant contained larger amounts of squalene and lanosterol (I) than the wild type, as well as 4,14-dimethylcholesta-8,24-dien-3beta-ol (II), 4,14-dimethylergosta-8,24(28)-dien-3beta-ol (III), and 14-methylergosta-8,24(28)-dien-3beta-ol (IV), which were not hitherto found in yeast. These results indicated a block in removal of the methyl group at C-14 of lanosterol. An ergosterol requiring derivative of the mutant which carried in addition a mutation in heme biosynthesis had the same sterols as the parent, but at one-third the concentration. The low level of sterols may be due to a requirement for a heme or cytochrome in oxygenation reactions between lanosterol and ergosterol.
73 citations
TL;DR: Gas-liquid chromatographic analyses of radioactive sterol composition after whole cell pulse experiments with [3H]squalene and with [ 3H]anosterol suggest that the fundamental enzymatic defect of the mutant is at the stage of lanosterol demethylation.
Abstract: A sterol-requiring mutant has been isolated from mutagenized Chinese hamster ovary cells. This mutant grows normally only when cholesterol is present in the medium. Cell lysis occurs within 3 days in the absence of cholesterol. The frequency of reversion of this mutant to prototrophic growth is low (less than or equal to 10(-6). Whole cell pulse experiments with [14C]acetate or [3H]mevalonate indicate that the rate of synthesis of digitonin-precipitable material is greatly diminished in the mutant cells as compared to that in normal Chinese hamster ovary cells. Enzyme assays in vitro with crude cell extracts show that the biosynthetic conversion of mevalonate to squalene and the conversion of squalene to lanosterol are not impaired in the mutant cells. Gas-liquid chromatographic analyses of radioactive sterol composition after whole cell pulse experiments with [3H]squalene and with [3H]anosterol suggest that the fundamental enzymatic defect of the mutant is at the stage of lanosterol demethylation. When cells were grown in serum-free medium, lanosterol and dihydrolanosterol accumulated intracellularly in the mutant cells before cell lysis occurred; neither of these two intermediary sterols was detected in the wild-type cells grown under the same condition.
56 citations
TL;DR: The compound 2,3;22,23-dioxidosqualene has been found to accumulate in yeast grown in the presence of 10−4m 3β-(β-dimethylaminoethoxy)-androst-5-en-17-one and subsequent removal of the latter compound permits the formation of 24,25-oxidolanosterol and more polar unidentified compounds.
48 citations
TL;DR: In this paper, Lanost-8-ene-3β,32-diol is synthesized and is shown to be demethylated by a rat liver microsomal preparation to give 4,4′-dimethylcholesta-8,14-dien-3 β-ol with the release of C-32 as formic acid.
45 citations
TL;DR: The distribution of the first eight triterpene alcohols in the seeds of eleven plants belonging to seven genera of Solanaceae family was determined.
44 citations
Journal Article•
TL;DR: Evidence in this report suggests that the postmicrosomal supernatant fraction of both liver and hepatoma contains a cytosolic protein that may participate in the regulation of the rate-determining attack of 4alpha-methyl sterol substrates.
Abstract: Previously, we reported that the properties of microsomal 4-methyl sterol demethylase isolated from liver and Morris hepatomas 5123C and 7777 are grossly similar. The individual enzymic steps of this multicomponent system have now been studied, and the rate-determining step has been determined and shown to be identical for liver and these hepatomas.
The rates of microsomal oxidative attacks of the 4α-methyl, 4α-hydroxymethyl, and 4-aldehydic groups are similar for microsomes prepared from rat liver and hepatoma 7777. The rates of mixed-function oxidative attack appear to increase in the order: —CH3 < —CH2OH < —CHO. Furthermore, the hepatic and hepatoma NAD-dependent decarboxylase, which catalyzes the reaction following the three oxidative attacks, is similar in properties and velocity. The fifth step, an NADPH-dependent reduction of the 3-ketosteroid that is produced by decarboxylation, is also similar. For both tissues, the latter two reactions, under in vitro conditions, proceed at rates that exceed the initial oxidative process. Thus, for elimination of both of the 4-methyl groups of lanosterol, the 10 individual reactions catalyzed in this multicomponent system are identical in liver and hepatoma 7777 microsomes, and the rate-determining step for both liver and hepatoma is the initial oxidative attack on the 4α-methyl group of cholesterol precursors.
When the rate-determining reaction of both liver and hepatoma 7777 microsomes is assayed at different temperatures, the same activation energies and the same characteristic breaks in the Arrhenius plots are observed. Thus, for both liver and hepatoma, both the nature and the site of rate determination in this multienzymic system must be similar.
Since the microsomal enzymes of liver and hepatoma appear to be catalytically similar and rate determination appears to be similar, too, the characteristic lack of response of tumor microsomes to treatments in vivo that alter host liver microsomal demethylation activity suggests that the insensitivity of these tumors to dietary cholesterol should not be ascribed to alterations in the catalytic proteins. Evidence in this report suggests that the postmicrosomal supernatant fraction of both liver and hepatoma contains a cytosolic protein that may participate in the regulation of the rate-determining attack of 4α-methyl sterol substrates. Thus, either qualitative or quantitative differences between the postmicrosomal supernatant fractions obtained from liver and hepatomas may account for the observed differences in rates of cholesterol biosynthesis.
31 citations
TL;DR: The results suggest that the major metabolic block in the pathway of sterol biosynthesis occurs between the step of farnesol and squalene, which supports significant population growth in all four nematodes.
Abstract: The quantitative sterol requirements were studied in C. briggsae, C. elegans (Be), C. elegans (Br), and T. aceti. It was shown that all four nematodes had similar minimal sterol requirements (0.1-2.0 μg/ml) and toxicity appeared in T. aceti at 50 μg/ml. Cholesterol and five precursors were tested for population growth. We found that acetic acid, DLmevalonic acid lactone, and farnesol did not support population growth; while squalene, lanosterol, and cholesterol supported significant population growth in all four nematodes. Our results suggest that the major metabolic block in the pathway of sterol biosynthesis occurs between the step of farnesol and squalene.
TL;DR: The authors showed that triparanol altered the sterol composition of Saccharomyces cerevisiae and promoted an increase in the steryl ester and total sterol per organism.
TL;DR: It is suggested that growth of the organism in the presence of defined amounts of delta-aminolaevulinate will be useful in the investigation of the role of lipids and cytochromes in the function and assembly of mitochondrial membranes.
Abstract: 1. The ole-3 mutant of Saccharomyces cerevisiae has an early lesion in the pathway of porphyrin biosynthesis. 2. This results in the loss of all haem-containing enzymes, including the mitochondrial cytochromes, and prevents the synthesis of components whose formation requires haem-containing enzymes, including unsaturated fatty acids, ergosterol and methionine. 3. The pleiotropic effects of the primary lesion are reversed by growing mutant ole-3 aerobically in the presence of intermediates of the porphyrin-biosynthetic pathway, and the present work reports the degree of manipulation of lipid and respiratory-cytochrome composition. 4. Supplements of delta-aminolaevulinate in the range 0.5--500 mg/l result in a progressive increase in the cellular content of unsaturated fatty acids and respiratory cytochromes, cause the replacement of lanosterol and squalene by ergosterol, and an increase in total sterol content. 5. Haematoporphyrin and protoporphyrin IX have similar but less extensive effects on cellular composition, whereas haematin allows unsaturated fatty acid synthesis and some sterol synthesis, but has no effect on the formation of respiratory cytochromes. 6. These results suggest that growth of the organism in the presence of defined amounts of delta-aminolaevulinate will be useful in the investigation of the role of lipids and cytochromes in the function and assembly of mitochondrial membranes.
TL;DR: The growth retardant action of triarimol and ancymidol in higher plants most likely results from inhibition of a reaction in the gibberellin biosynthetic pathway analogous to sterol C-14 demethylation.
Abstract: Triarimol and triforine inhibit ergosterol biosynthesis in fungi and cause accumulation of free fatty acids, 24-methylenedihydrolanosterol, obtusifoliol and 14α-methyl-δ8,24(28)-ergostadienol. Triparanol also inhibits ergosterol synthesis and causes accumulation of free fatty acids, but not of the latter 3 sterols. Triparanol appears to inhibit prior to lanosterol in the sterol biosynthetic pathway of Ustilago maydis and at unidentified sites subsequent to lanosterol which lead to the accumulation of a sterol which migrates with desmethylsterols on TLC plates. Quantitative abnormalities in sterols and free fatty acids in U. maydis are not produced by the fungicides carbendazim, chloroneb, carboxin and cycloheximide. A deficiency in nitrogen leads to a marked increase in triglycerides, but a normal distribution pattern for other lipids.
TL;DR: The metabolism of lanosterol and 24,25-dihydrolanosterol was examined in a patient with cerebrotendinous xanthomatosis, and isotope ratio measurements and specific activity decay curves suggested that reduction of the Lanosterol side chain may occur as an early step in the synthesis of cholesterol.
Abstract: The metabolism of lanosterol and 24,25-dihydrolanosterol (DL) was examined in a patient with cerebrotendinous xanthomatosis after intravenous pulse labeling with a mixture of DL-2-14C and 3S,4S,3R,4R-(4-3H)mevalonate. Sterols were isolated from the feces and purified by silver nitrate thin-layer chromatography, and their identities were confirmed by gas-liquid chromatography and mass spectrometry. Their specific activities were then determined and plotted as a function of time. These isotope ratio measurements and specific activity decay curves were consistent with 24,25-dihydrolanosterol and delta7-cholestenol being intermediates in the synthesis of cholesterol from mevalonate and lanosterol, and they suggested that reduction of the lanosterol side chain may occur as an early step in the synthesis of cholesterol. These results are in contrast to the results reported after the administration of triparanol, a delta24-reductase inhibitor.
TL;DR: Lanosterol and lanostenol, whose occurrence in higher plants has hitherto been known as extremely rare, are identified in the fraction by gas liquid chromatography, combined gas liquid Chromatography-mass spectrometry, and isolation as their epoxides.
TL;DR: It appears therefore, that the squalene which escapes incorporation into cholesterol is degraded to metabolite(s) suited for the synthesis of isoprene compounds.
Abstract: (1) Radioactivity of biosynthetically labeled squalene, injected in tracer amounts in rats is incorporated to about equal parts into cholesterol and component(s) of the fatty acid fraction of the liver. The ubiquinones isolated from the liver are radioactive and show about the same specific radioactivity as the cholesterol. It appears therefore, that the squalene which escapes incorporation into cholesterol is degraded to metabolite(s) suited for the synthesis of isoprene compounds.
(2) Radioactivity of injected biosynthetically and chemically labeled cholesterol is traced in the ubiquinones and the squalene of rat liver indicating that a degradation of cholesterol and a recycling of the metabolite(s) occurs.
(3) A recycling of metabolite(s) of squalene and of cholesterol can explain the observation that after labeled mevalonate or acetate as precursor, radioactivity can be traced in the squalene of the liver many hours after the injection and maintains a constant value during a period of several hours.
(4) Radioactivity of biosynthetically labeled lanosterol is not only incorporated into cholesterol but a considerable part of it into component(s) of the bile acid fraction of the liver. Evidence is obtained that this transformation occurs by circumventing cholesterol as intermediate.
TL;DR: In this article, the stereochemistry of the hydrogen atom migration from C-24 to C-25 has been established during the biosynthesis of isofucosterol from lanosterol in Pinus pinea.
Abstract: During the biosynthesis of isofucosterol from lanosterol in Pinus pinea the stereochemistry of the hydrogen atom migration from C-24 to C-25 has been established.
TL;DR: It was evident that Denmert directly affects the enzymatic formation of ergosterol, selectively inhibiting the demethylation at the C-14 position of the sterol nucleus.
Abstract: Effects of the fungicide Denmert on sterol biosynthesis were examined. The rates of inhibition of ergosterol formation were roughly correlated to its fungitoxic activity among four fungal species tested. In cell-free homogenates of yeast (S. cerevisiae), the fungicide blocked the conversion of lanosterol to 14-desmethyl-lanosterol. It was evident that Denmert directly affects the enzymatic formation of ergosterol, selectively inhibiting the demethylation at the C-14 position of the sterol nucleus. The fungicide triarimol was found to exhibit the same effects on sterol biosynthesis as Denmert in cell-free homogenates of yeast.
TL;DR: Dihydroagnosterol is demethylated by a rat liver homogenate to give 4,4'-dimethylcholesta 7,9-dienol and then cholesta-7, 9- dienol, which is converted into cholesterol by the normal pathway.
Abstract: Dihydroagnosterol is demethylated by a rat liver homogenate to give 4,4'-dimethylcholesta 7,9-dienol and then cholesta-7,9-dienol. The cholesta-7,9-dienol is isomerized to cholesta-8,14-dienol, which is converted into cholesterol by the normal pathway.
01 Jan 1977
TL;DR: The most detailed knowledge of terpenoid biosynthesis comes from studies with rat liver systems as mentioned in this paper, which established in complete stereochemical detail the formation of squalene, lanosterol and cholesterol.
Abstract: In spite of their extraordinary structural variety and complexity all mevalonoids derive from one simple C6 compound, (R)-mevalonic acid (1). This was discovered (34) by Folkers and his colleagues in 19 56 in dried distillers’ solubles and shown to replace acetate as a growth factor for Lactobacillus acidophilus. In the same year Tavormina, also at the Merck laboratories, found (32) that racemic mevalonic acid was efficiently (43.4%) incoporated into cholesterol by rat liver homogenates. Thereafter, mevalonic acid was rapidly recognized as the progenitor of the “biogenetic isoprene unit,” isopentenyl pyrophosphate, and hence of all mevalonoids. Our most detailed knowledge of terpenoid biosynthesis comes from studies with rat liver systems. This includes the superb work of Cornforth, Popjak and their colleagues (11), which established in complete stereochemical detail the formation of squalene, lanosterol and cholesterol. Beyond this, the most fruitful studies to date of mevalonoid biosynthesis have been carried out with fungal metabolites. Verrucarol (2), gibberellic acid (3) and ophiobolin A (4) provide three examples of fungal terpenoids of complex and contrasting structural types whose biosynthesis has been studied in detail (2, 12, 9).
TL;DR: It is shown that the isoprenic synthesis is inhibited between squalene and Lanosterol but that other regulation site(s) after the lanosterol formation must exist, and another regulating site controlling the utilization of acetylcoenzyme A for the synthesis of mevalonate is also shown to exist.
Abstract: (1)
The existence of a main regulation site(s) of the cholesterol synthesis located after the squalene formation is demonstrated by cholesterol feeding with labelled glucose, acetate, mevalonate as precursors and by measuring the incorporation rates into cholesterol, squalene, ubiquinones, and fatty acids in rat liver in vivo.
(2)
By administration of labelled squalene in vivo it is shown that the isoprenic synthesis is inhibited between squalene and lanosterol but that other regulation site(s) after the lanosterol formation must exist.
(3)
A regulation site of the cholesterogenesis in rat liver located after the squalene synthesis is also shown after a lipogenic diet administered during 5 days. The cholesterol synthesis is thus reduced to about one third of the control rats. Another regulating site controlling the utilization of acetylcoenzyme A for the synthesis of mevalonate is also shown to exist. No indication was obtained for a regulating influence located between mevalonate and squalene.