Differential effects of plant sterols on water permeability and on acyl chain ordering of soybean phosphatidylcholine bilayers.
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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 phosphatidylcholine (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 24zeta-methylcholesterol 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. Of two unusual plant sterols, 24-methylpollinastanol and 14alpha,24zeta-dimethylcholest-8-en-3beta-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-methylpollinastanol. The results provided clear evidence that sitosterol and 24zeta-methylpollinastanol 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 Delta22 double bond in the side chain, probably play different roles in regulating plant membrane properties; they also may explain why 9beta,19-cyclopropylsterols behave as good surrogates of sitosterol.Keywords:
Stigmasterol
Cycloartenol
고산 홍경천에 포함된 스테로이드 화합물의 구성을 흡착 컬럼 크로마토그래픽 정제와 GC/MS를 이용하여 측정하였다. 스테롤은 에탄올과 디클로로메탄을 각각 초음파와 Soxhlet의 용매로 사용하여 추출하였다. 추출물은 클로로포름과 물로 액-액 추출을 수행하여 분배하였으며, 실리카 컬럼으로 정제하였으며, BSTFA를 사용하여 silyl유도 반응을 수행하였다. GC/MS를 이용하여 고산 홍경천에서 β-sitosterol, stigmasterol과 cycloartenol을 포함한 18가지 자유 스테롤과 9가지 포합체 스테롤을 검출할 수 있었다. 그중에서 cholest-5-ene-3-ol, cholesterol, stigmasterol, β-sitosterol은 스테롤 표준품으로 확인하고 정량분석을 수행하였다. 대부분의 스테롤은 클로로포름 분액에서 검출되었고, C29는 여러 그룹 중에서 가장 많은 그룹이었다. β-sitosterol은 가장 많이 함유된 성분이며 상대함량은 45.94%이고, 차례로 ergost-7-ene-3-ol(11.33%), 4,14-dimethyl-ergosta-8,24(28)-diene-3-ol (7.07%), stigmasterol (6.09%), cycloartenol (5.43%)과 4-methyl-cholest-5-ene-3-ol (5.39%)이었다.
Stigmasterol
Cycloartenol
BSTFA
Cholestane
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Stigmasterol
Phytosterol
Cycloartenol
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Stigmasterol
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Stigmasterol
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Stigmasterol
Cycloartenol
Phytosterol
Chemotaxonomy
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Sterol levels in dandelion (Taraxacum officinale Weber) leaves were monitored over a period of 19 months. Sitosterol was the most abundant free sterol, followed by stigmasterol, then campesterol. Cholesterol could not be detected. With the exception of stigmasterol and campesterol, esters were present in greater quantities than were free forms, with 4,4-dimethyl sterol esters being the most abundant type. Glycosides occurred only sporadically. Free 4-demethyl sterols were maximal during the winter months; levels correlated negatively with sunshine and temperature, but proportions did not alter significantly. Sitosterol ester and cycloartenol ester (but not others) showed the opposite response, with levels correlating positively with sunshine and temperature. Relative amounts of 4-demethyl sterol esters remained reasonably constant, but those of cycloartenol ester and 24-methylene cycloartanol ester varied on an annual basis and were negatively correlated with each other.
Cycloartenol
Stigmasterol
Taraxacum officinale
Phytosterol
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Cycloartenol
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Phytosterol
Desmethyl
Cholestanol
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Stigmasterol
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Methylene
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Sterol composition and biosynthesis have been examined in seeds, germinating seeds and blades from fally matured leaves ofSorghum bicolor in various stages of development'from seedlings (seven-day plants) to flowering (66-day) plants. The profile of the dominant free sterols of seeds was similar to that of leaf blades; both contained cholesterol, 24α-methylcholesterol (campesterol), 24β-methylcholesterol (dihydrobrassicasterol), 24α-ethylcholesterol (sitosterol) and 24α-ethylcholesta-5,22-dienol (stigmasterol). Sufficient sterol intermediates were identified in the plant to indicate separate post-cycloartenol pathways to sterolic end products. The total free sterol content of the seed (μg/seed) increased somewhat during the 20 hr germination period. However, as the plant developed (seven to 48 days), there was a logarithmic increase in the leaf blade sterol content (μg/leaf blade) which plateaued at the onset of floral differentiation (ca. day 41). Over the next 18 days (48 to 66 days-period of inflorescense development), the sterol content rapidly decreased. In the early stages of plant development, the leaf blade pentacyclic triterpenoid (PT) content was negligible. With the onset of floral differentiation, PT content increased logarithmically, reaching a plateau level that surpassed the sterol content as flowering progressed. These results imply that a critical mass of sterol is associated with sorghum for floral induction. Sterol loss from the leaves of the flowering plants presumably was compensated for by the diversion of 2,3-oxidosqualene (SO) from sterol synthesis to PT production. Additional feeding and trapping experiments with [2-(14)C]mevalonic acid, [2-(3)H]cycloartenol, [24-(3)H]lanosterol [4-(14)C]sitosterol and [4-(14)C]cholesterol fed to germinating seeds and leaves from flowering plants demonstrated that sorghum possessed a cycloartenolbased pathway; germinating seeds synthesized 24-alkylsterols but not cholesterol, although cholesterol was identified in both dry and germinating seeds by gas chromatography-mass spectroscopy (GC-MS); and mature leaves synthesized cholesterol and 24α-alkylsterols but not 24β-methylcholesterol.
Cycloartenol
Stigmasterol
Lanosterol
Phytosterol
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