A Comparison of Triterpenoids with Steroids as Membrane Components

Nes, W. David; Heftmanń, Erich

doi:10.1021/np50016a001

Cited by 79 publications

(39 citation statements)

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“…They also were less efficient than cholesterol in reducing the methanol-induced f3-cyanine efflux from red beet disks (26). Cholesterol has therefore been considered for a long time to be the standard reference for sterol effects on membranes (1,27,28 In contrast, stigmasterol, another major sterol in higher plant membranes, was found to have no significant effect on the swelling rate of soybean PtdCho vesicles (Table 1). In egg PtdCho vesicles, this sterol has been shown to be far less efficient than cholesterol in reducing the membrane permeability to glycerol and erythritol (22).…”

Section: Discussionmentioning

confidence: 99%

Differential effects of plant sterols on water permeability and on acyl chain ordering of soybean phosphatidylcholine bilayers.

Schuler

Milon

Nakatani

et al. 1991

Proc. Natl. Acad. Sci. U.S.A.

210

150

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To gain some insight into the structural and functional roles of sterols in higher plant cells, various plant sterols have been incorporated into soybean phosphatidyicholine (PtdCho) bilayers and tested for their ability to regulate water permeability and acyl chain ordering. Sitosterol was the most efficient sterol in reducing the water permeability of these vesicles and stigmasterol appeared to have no significant effect.Vesicles containing 24fmethylcholesterol exhibited an intermediate behavior, similar to that of vesicles containing cholesterol. Cycloartenol, the first cyclic biosynthetic precursor of plant sterols, reduced the water permeability in a very effective way. Oftwo unusual plant sterols, 246-methylpollinastanol and 14a,24Udimethylcholest-8-en-3fi-ol, the former was found to be functionally equivalent to sitosterol and the latter was found to be relatively inefficient. 2H NMR experiments have been performed with oriented bilayers consisting of soybean PtdCho with sitosterol, stigmasterol, or 24-methylpoll nastanol. The results provided clear evidence that sitosterol and 24k-methylpolinastanol exhibit a high efficiency to order PtdCho acyl chains that closely parallels their ability to reduce water permeability. By contrast, stigmasterol shows a low efficiency for both functions. These results show that sitosterol and stigmasterol, two major 24-ethylsterols differing only by the absence or presence of the A22 double bond in the side chain, probably play different roles in regulating plant membrane properties; they also may explain why 9P,19-cyclopropylsterols behave as good surrogates of sitosterol.In mammalian cells, the bulk of free cholesterol is localized in the plasma membrane where it participates in the regulation of membrane fluidity and in the activity of many membrane-bound enzymes (1). Changes in cholesterol content have been shown to induce modifications in cellular functions, which depend on the dynamics of the cell-surface membrane such as the recognition of an external signal (1). In higher plant cells, the three typical phytosterols: sitosterol, and 24F-methylcholesterol [the mixture of 24R (i.e., campesterol) and 24S (i.e., 22-dihydrobrassicasterol) epimers] are also mainly concentrated in the plasma membrane (2). To investigate whether the different plant sterols play similar roles in higher plant cells, we started a study with well-defined model membrane systems prepared from soybean phosphatidylcholine (PtdCho), a major representative plant phospholipid, and various sterols in different molar ratios. Because of their high content in polyunsaturated fatty acyl chains (3), soybean PtdCho bilayers can be considered a valuable model of higher plant membrane. The present work deals with the effect of some plant sterols on water permeability and acyl chain ordering of these bilayers. Permeability changes were monitored by measuring the swelling rates of large unilamellar vesicles (LUVs) following an osmotic shock in a stopped-flow spectrophotometer. This method had been develo...

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Section: Discussionmentioning

confidence: 99%

Differential effects of plant sterols on water permeability and on acyl chain ordering of soybean phosphatidylcholine bilayers.

Schuler

Milon

Nakatani

et al. 1991

Proc. Natl. Acad. Sci. U.S.A.

210

150

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“…In membranes from fenpropimorph-treated tissues, the remaining A5-sterols are present only in very low amounts (3-5% of total sterols). It is possible that these trace levels of usual sterols play nonstructural, specific roles and are involved in some metabolic functions that remain to be investigated (21). About half of the accumulating cyclopropyl sterols are 4a-methyl sterols, whereas such sterols, which are precursors of A5-sterols, are minor compounds in control plants.…”

Section: Discussionmentioning

confidence: 99%

Cyclopropyl Sterol and Phospholipid Composition of Membrane Fractions from Maize Roots Treated with Fenpropimorph

Grandmougin¹,

Bouvier-Navé²,

Ullmann³

et al. 1989

Plant Physiol.

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Maize (Zea mays L.) caryopses were grown in the presence of fenpropimorph, a systemic fungicide, for 7 days in the dark. Membrane fractions enriched, respectively, in endoplasmic reticulum, plasma membrane, and mitochondria were isolated from control and treated maize roots and analyzed for their free sterol, phospholipid, and fatty acid composition. In treated plants, the intracellular distribution of free sterols was dramatically modified both qualitatively and quantitatively. The normally occurring A5-sterols disappeared almost completely and were replaced by 9,B,19-cyclopropyl sterols, mainly cycloeucalenol and 24-methyl pollinastanol. These new compounds were found to accumulate in all the membrane fractions in such a way that the endoplasmic reticulum-rich fraction became the richest one in free sterols instead of the plasma membrane. In contrast, the fenpropimorph treatment of maize roots was shown not to affect either the relative proportions or the amounts of the individual phospholipids, but an increase in the unsaturation index of phospholipidfatty acyl chains of the endoplasmic reticulum-rich fraction was observed. The present data suggest that, in higher plant membranes, cyclopropyl sterols could play a structural role similar to that of the bulk of A5-sterols.Whereas animal and fungal cells generally contain one major sterol, respectively, cholesterol (1)1 and ergosterol (17), ' Chemical nomenclature: cholesterol (1), cholest-5-en-3,B-ol; 24-methyl cholesterol (2), (24r)-24-methylcholest-5-en-3(3-ol; stigmas-(28)Z-dien-3f-ol; 24-methyl pollinastanol (6), (24r)-24,14a-dimethyl-9fl, 19-cyclo-5a-cholestan-3#-ol; 24-methylene pollinastanol (7), 14a-methyl-9f,19-cyclo-5a-ergost-24(28)-en-33-ol; 24-ethyl pollinastanol (8), 14a-methyl-9j3, 19-cyclo-5a-stigmastan-3f-ol; obtusifoliol (9), 4a, 14a-dimethyl-5a-ergosta-8,24(28)-dien-3(-ol; cycloeucalenol (10), 4a, 14a-dimethyl-9(, 19-cyclo-5a-ergost-24(28)-en-3(-ol; 24-dihydrocycloeucalenol (11), (24R)-24,4a, 14a-trimethyl-9,B, 19-cyclo-5a-cholestan-3,B-ol; 31-norcyclobranol (12), 4a,14a-dimethyl-9,3,19-cyclo-5a-ergost-24(25)-en-3fl-ol; cyclofuntumienol (13), 4a, 14a-dimethyl-93,19-cyclo-5a-stigmast-24(28)Z-en-3,3-ol; cycloartenol (14), 4,4,14a-trimethyl-9,B, 19-cyclo-5a-cholest-24-en-3,-ol; 24-methylene cycloartanol (15), 4,4,14a-trimethyl-93, 19-cyclo-5a-ergost-24(28)-en-33-ol; f-amyrin (16), olean-12-en-3,B-ol; ergosterol (17), (24R)-24-methylcholesta-5,7,22E-trien-3,B-ol; fenpropimorph, (R,S)-4-[3-(4-tert-butylphenyl)-2-methyl-propyl]-2,6-dimethylmorpholine.in most higher plants, sterols are present as mixtures in which 24-methyl cholesterol (2), stigmasterol (3), and sitosterol (4) often predominate (20). These A5-sterols mostly accumulate in the plasma membrane (pM)2 (13), where they are believed to regulate the membrane fluidity and, consequently, the activity of membrane-bound enzymes. In addition to this structural role, a few sterol molecules might be involved in metabolic functions. To obtain a better insight into sterol functions in plant...

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“…The fate of ␤-amyrin in these other cells is not known. Triterpenoids may act as structural components of membranes under certain conditions in some plant tissues (5,34). Alternatively other minor nonfluorescent avenacins (16,17) may be produced in the inner part of the root.…”

Section: Expression Of Asbas1 In Oatsmentioning

confidence: 99%

A new class of oxidosqualene cyclases directs synthesis of antimicrobial phytoprotectants in monocots

Haralampidis

Bryan²,

Qi³

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

167

204

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Here we show the novel oxidosqualene cyclase AsbAS1 catalyzes the first committed step in the synthesis of antifungal triterpenoid saponins that accumulate in oat roots. We also demonstrate that two sodium azide-generated saponin-deficient mutants of oat, which define the Sad1 genetic complementation group, are defective in the gene encoding this enzyme and provide molecular genetic evidence indicating a direct link between AsbAS1, triterpenoid saponin biosynthesis, and disease resistance. Orthologs of AsbAS1 are absent from modern cereals and may have been lost during selection, raising the possibility that this gene could be exploited to enhance disease resistance in crop plants.

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A Comparison of Triterpenoids with Steroids as Membrane Components

Abstract: TABLE 1. Prokaryotic organisms containing sterols or triterpenoids.

Cited by 79 publications

References 1 publication

Differential effects of plant sterols on water permeability and on acyl chain ordering of soybean phosphatidylcholine bilayers.

Differential effects of plant sterols on water permeability and on acyl chain ordering of soybean phosphatidylcholine bilayers.

Cyclopropyl Sterol and Phospholipid Composition of Membrane Fractions from Maize Roots Treated with Fenpropimorph

A new class of oxidosqualene cyclases directs synthesis of antimicrobial phytoprotectants in monocots

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