Steryl esters in a cell suspension culture of celery (Apium graveolens)

Effects of exogenous mevalonic acid on sterol lipid classes in Larix kaempferi callus

In Japanese larch (Larix kaempferi (Lamb.) Carr.) calli, free sterol (FS), acylsterol (AS) and glycosylsterol, including the acylated type, were found in the proportion of 1.0:0.1:0.8. When the calli were cultured in the presence of 10 mM mevalonic acid (MVA), the content of AS, but not FS and glycosylsterol, was increased remarkably. The major component sterol in each sterol lipid class was usually sitosterol (more than 90%) with campesterol as a minor one. There were no differences on the sterol compositions between the calli cultured with or without MVA. When the calli cultured with 10 mM MVA for 6 weeks were transferred to the control medium without exogenous MVA, AS contents decreased to the level of the control calli. Thus, it was shown that sterol lipids, such as FS and glycosylsterols, with the structural functions was maintained in the constant content and the excess sterol biosynthesized from exogenous MVA was esterified to form AS for storage of sterol components.

Three series of high molecular weight alkanoates found in Amazonian plants

Electron impact mass spectra were measured by high temperature high resolution gas chromatography-mass spectrometry (HT-HRGC-MS) for three homologous series of high molecular weight compounds present in the Amazonian plants Marupá (Simaruba amara) and Brazil nut (Bertholettia excelsa). Based on their mass spectra, the compounds were identified as three wax ester series of alpha-tocopherol (vitamin E), beta-tocopherol and phytol (2,6,10,14-tetramethylhexadec-14-en-16-ol). The interpretations are supported by high resolution mass spectrometry and GC retention indices of authentic standards.

Analysis of free and esterified sterols in fats and oils by flash chromatography, gas chromatography and electrospray tandem mass spectrometry

A method for the analysis of free and esterified sterols has been developed. Fat or oil samples were separated on solid-phase extraction silica gel columns into a sterol ester fraction, a fraction of triacylglycerols, and a free sterol fraction containing partial acylglycerols and residual triacylglycerols. Sterol esters and acylglycerols of the free sterol fraction were transesterified to methyl esters. The fatty acid methyl esters from sterol ester fraction and the free sterols from sterol ester fraction and free sterol fraction were determined by GLC. Precursor ion electrospray MS-MS of sterol fragment ions of sterol ester fractions were recorded and used for determination of sterol ester proportions in butterfat and vegetable oil samples.

UDP-glucose sterol beta-D-glucosyltransferase, a plasma membrane-bound enzyme of plants: enzymatic properties and lipid dependence

UDP-glucose sterol beta-D-glucosyltransferase (UDPG-SGTase) catalyzes the glucosylation of plant sterols. This enzyme has been shown to be membrane-bound, most of its activity being associated with plasma membrane in etiolated maize coleoptiles. After solubilization with detergents, total delipidation and purification, kinetic studies performed with a purified enzyme preparation in the presence of detergent and soybean phosphatidylcholine (PC) strongly suggest an ordered bi-bi mechanism for the glucosylation of sterols. A reduced sulfhydryl group and an arginyl residue were shown to be essential for activity. Lipid dependence studies have been performed on the delipidated enzyme in two systems: a micellar one composed of a mixture of enzyme, detergent and phospholipids and another one where the enzymatic activity was reconstituted in unilamellar lipid vesicles. In both systems it was shown that the UDPG-SGTase activity was stimulated to a large extent by negatively charged phospholipids. Enzymatic assays were performed with membrane fractions originating from plants whose sterol content was profoundly modified following treatment with a sterol biosynthesis inhibitor. Results showed that the sterol glucosylating activity was strongly inhibited in these fractions in accordance with sterol substrate specificity studies. All these results show that the UDPG-SGTase is exquisitely sensitive to its lipid environment. Physiological implications of these data are discussed in the light of the putative role of sterols in the plant cell.

Analysis of sterol esters from alga and yeast by high-performance liquid chromatography and capillary gas chromatography-mass spectrometry with chemical ionization

Sterol esters from the green alga Chlorella kessleri and the yeast Saccharomyces cerevisiae were analysed by tandem high-performance liquid chromatography (HPLC-HPLC). Non-polar lipids were separated by normal-phase HPLC into individual classes and the fraction of sterol esters was subsequently separated by reversed-phase HPLC into intact molecular species. Further separation and identification of the fractions after HPLC were effected by capillary gas chromatography-mass spectrometry (cGC-MS) with positive and/or negative chemical ionization. A technique consisting of direct injection of the sample after its passage through the detector into the on-column injector of the gas chromatograph was used to transfer the sample from HPLC-HPLC to cGC-MS. By means of this method it was possible to demonstrate more than 30 sterols in both the alga and the yeast, and more than 20 new sterol esters were detected.