Characterization Of Sterols Research Articles

Characterization of the Sterol 24-C-Methyltransferase Genes Reveals a Network of Alternative Sterol Biosynthetic Pathways in Mucor lusitanicus.

Certain members of the order Mucorales can cause a life-threatening, often-fatal systemic infection called mucormycosis. Mucormycosis has a high mortality rate, which can reach 96 to 100% depending on the underlying condition of the patient. Mucorales species are intrinsically resistant to most antifungal agents, such as most of the azoles, which makes mucormycosis treatment challenging. The main target of azoles is the lanosterol 14α-demethylase (Erg11), which is responsible for an essential step in the biosynthesis of ergosterol, the main sterol component of the fungal membrane. Mutations in the erg11 gene can be associated with azole resistance; however, resistance can also be mediated by loss of function or mutation of other ergosterol biosynthetic enzymes, such as the sterol 24-C-methyltransferase (Erg6). The genome of Mucor lusitanicus encodes three putative erg6 genes (i.e., erg6a, erg6b, and erg6c). In this study, the role of erg6 genes in azole resistance of Mucor was analyzed by generating and analyzing knockout mutants constructed using the CRISPR-Cas9 technique. Susceptibility testing of the mutants suggested that one of the three genes, erg6b, plays a crucial role in the azole resistance of Mucor. The sterol composition of erg6b knockout mutants was significantly altered compared to that of the original strain, and it revealed the presence of at least four alternative sterol biosynthesis pathways leading to formation of ergosterol and other alternative, nontoxic sterol products. Dynamic operation of these pathways and the switching of biosynthesis from one to the other in response to azole treatment could significantly contribute to avoiding the effects of azoles by these fungi. IMPORTANCE The fungal membrane contains ergosterol instead of cholesterol, which offers a specific point of attack for the defense against pathogenic fungi. Indeed, most antifungal agents target ergosterol or its biosynthesis. Mucormycoses-causing fungi are resistant to most antifungal agents, including most of the azoles. For this reason, the drugs of choice to treat such infections are limited. The exploration of ergosterol biosynthesis is therefore of fundamental importance to understand the azole resistance of mucormycosis-causing fungi and to develop possible new control strategies. Characterization of sterol 24-C-methyltransferase demonstrated its role in the azole resistance and virulence of M. lusitanicus. Moreover, our experiments suggest that there are at least four alternative pathways for the biosynthesis of sterols in Mucor. Switching between pathways may contribute to the maintenance of azole resistance.

Recent developments and applications of clickable photoprobes in medicinal chemistry and chemical biology.

Photoaffinity labeling is a well-known biochemical technique that has grown significantly since the turn of the century, principally due to its combination with bioorthogonal/click chemistry reactions. This review highlights new developments and applications of clickable photoprobes in medicinal chemistry and chemical biology. In particular, recent examples of clickable photoprobes for target identification, activity- or affinity-based protein profiling (ABPP or AfBPP), characterization of sterol- or lipid-protein interactions and characterization of ligand-binding sites are presented.

Evolution of phytosterols in Chardonnay grape berry skins during last stages of ripening

This study presents the results of rapid phytosterols analysis in grape skins during last stages of ripening. The analysis is related to the evolution of sterol content by comparison with ripening degree on two vineyards of Chardonnay grape variety in Burgundy: Meursault ler Cru and Hautes Cotes de Beaune. The characterization of sterols is realized by using combined gas chromatography-mass spectrometry from trimethylsilyl ethers of sterols. After optimization of extraction by azeotropic mixture (chloroform/methanol 2:1 v/v), the analysis allows to identify four sterols in grape skins: beta-sitosterol, campesterol, stigmasterol and lanosterol. In all the samples, beta-sitosterol is the major phytosterol (86 to 89 % of the total detected phytosterols). The evolution of phytosterols content during last stages of ripening shows a similar comportment of β-sitosterol, campesterol and stigmasterol in grape skins: the maturation induces a loss of phytosterols in grape skins. An increase of phytosterol contents occurs at peak maturity and can be related with over-maturation phenomenon. The relationship between phytosterol content in grape skins and S/A ratio indicates a markedly negative correlation.

Characterization of sterols in refined borage oil by GC‐MS

AbstractBorage oil sterols were isolated by TLC and characterized using GC and GC‐MS. Several diunsaturated Δ5‐sterols, some of them not previously recorded in vegetable oils, were found. Of these, 24‐methylcholesta‐5,23‐dienol and 24‐ethylcholesta‐5,23‐dienol could be useful markers for borage oil. Two other diunsaturated Δ5‐sterols that are rarely found in vegetable oils, 24‐methylcholesta‐5,24(25)‐dienol and 24‐ethylcholesta‐5,24(25)‐dienol, were identified. The diunsaturated C‐24(28)‐sterol, isofucosterol, was also found, as well as the monounsaturated Δ5‐sterols campesterol and sitosterol. These are normally present in vegetable oils, which makes them unsuitable as markers for borage oil.

GC-MS characterization and quantification of sterols and cholesterol oxidation products

A GC-MS method has been studied for characterization and quantification of phytosterols, cholesterol and cholesterol oxidation products. Baseline separations have been achieved between cholesterol, cholesterol 5α-6α-epoxide, 5-cholestene-3β-ol-7one (7-keto-cholesterol), cholestene-3β-5α-6β-triol, 5-cholestene-3β-25-diol (25-hydroxycholesterol), 5-cholestene-3β-20α-diol (20α-hydroxycholesterol), 5-cholestene-3β-7β-diol (7β-hydroxycholesterol) and 5-cholestene-3β-19-diol (19-hydroxycholesterol) as well as between α-cholestane, cholesterol, stigmasterol, campesterol and β-sitosterol. Excellent linearity of response has been obtained permitting reliable quantification. The characterization of each derivatized sterol has been performed by mass-spectrometry. The results confirm the utility of combined gas chromatography-mass spectrometry in the analysis and characterization of sterols and cholesterol oxidation products.

Studies on the Sterols and Triterpene Alcohols of Vegetable Oils

Studies on the constituents of sterols, 4α-methylsterols, and triterpene alcohols in a number of vegetable oils have led to the identification and characterization of one twenty-eight compounds in all (fifty-six of sterols, thirty-one of 4α-methylsterols, and forty-one of triterpene alcohols) which included a number of compounds detected for the first time in higher plants, in addition to twenty-eight new or newly found natural products. The occurrence and distribution of these compounds in vegetable oils were extensively investigated. In addition to these, the characterization of sterols and triterpene alcohols has been studied with the aid of gas chromatography, especially on glass capillary columns, and nuclear magnetic resonance (NMR) spectroscopy. The determination of the stereochemistry at C-24 of a large number of 24-alkylated sterols, 4α-methylsterols, and tetracyclic triterpene alcohols was performed with high-resolution 1H-NMR and 13C-NMR spectroscopy.

Characterization of sterols of three digenetic trematodes of buffalo

Sterols of three digenetic trematodes were isolated and characterized by infrared and 1H nuclear magnetic resonance spectroscopies, and gas-liquid chromatography and gas chromatography-mass spectrometry. Sterols identified were cholesterol, cholestanol, 24-methylcholesterol, 24-methylcholestanol, 24-ethyl-22-dehydrocholesterol, 24-ethyl-22-dehydrocholestanol, 24-ethylcholesterol and 24-ethylcholestanol.

Isolation and characterization of sterols and an aliphatic alcohol from <i>Tsuga dumosa</i> D. Don of Nepal

In the course of our continuing research on Himalayan conifers, the phytochemical screening and isolation of chemical constituents of Tsuga dumosa D. Don of Nepali origin was carried out. Three sterols, namely â-sitosterol (1), stigmasterol (2), â-sitosterol glucoside (3) and an alcohol, nonacosan-10-ol (4) were isolated. Their structures were elucidated on the basis of spectroscopic evidences. Key Words: Phytochemical screening; Tsuga dumosa; Sterols; Nonacosan-10-ol. DOI: http://dx.doi.org/10.3126/sw.v9i9.5511 SW 2011; 9(9): 16-17

Characterization of sterols by gas chromatography‐mass spectrometry of the trimethylsilyl ethers

The utility of combined gas chromatography-mass spectrometry in the analysis and characterization of sterols has been explored. Methylene unit (MU) values and principal mass spectrometric data are presented for trimethylsilyl ethers of 28 sterols, including the major natural sterols. The diagnostic value of the fragmentation of trimethylsilyl ethers of Delta(5)-3 beta-hydroxysteroids has been confirmed. Characteristic fragmentations of Delta(4)-3 beta-trimethylsilyloxysteroids, and of Delta(5,7)-3 beta-trimethylsilyloxysteroids were also found. Location of side-chain hydroxyl groups is facilitated by the alpha-cleavages typical of the trimethylsilyl ethers. Fragmentations of saturated sterols, and of Delta(7), Delta(8(9)) and Delta((14)) stenols, are less influenced by trimethylsilyl ether formation, but the derivatives still afford satisfactory mass spectra. The combination of gas chromatographic and mass spectrometric information allows positive identification of any of the sterols examined, whereas application of either technique alone may give inconclusive results.