Sterols occurrence

With certain Oomycetes, "sterol-like molecules, eg. tetracyclic and pentacyclic triterpenoids (Fig. 2), may produce the same physiological end response as sterols (2). The growth response to these polycyclic isopentenoids is intimately associated with their 3-dimen-sional geometry, molecular features and subcellular quantity. In order to discuss sterol function for What we assume is an evolutionary determinant of developmental change, a brief overview of sterol occurrence and biosynthesis is given first. 

Table 2. Occurrence of the Provitamins D in Selected Plants and Animals, Parts per Thousand of Total Sterol...

Establishment of the dietary or symbiotic origin of sterols could be a difficult task, unless the tracer sterol has an unusual structure and restricted occurrence. There is little doubt, for example, that petrosterol (59) found in the nudibranch Peltodoris atromaculata [112] arises from predation of the mollusc on the sponge Petrosia ficiformis, from which the sterol was first isolated [113]. However, the origin of gorgosterol (60) in Tridacna species has not yet been established [114] despite its unusual structure. 

Studies of Gossypiim metabolites have uncovered the occurrence of a few plant sterols, including the representative 3-sitosterol (219) (, 1, 59). These widely occurring phyto-... 

Ballantine, J.A. Lavis, A. Roberts, J.C. Morris, R.J. (1977) Marine sterols. V. Staol of some tunicata. The occurrence of saturated ring sterols in these filter-feeding aganisms. J. Exp. Mar. Biol. Ecol., 30,29-44. 

The rearrangement of this initially created C-20 carbocation to lanosterol (Fig. 22-6, step c) is also a remarkable reaction that requires the shift of a hydride ion and of two methyl groups, as indicated by the arrows in the figure. In addition, a hydrogen at C-9 (sterol numbering) is lost as a proton. Lanosterol is named for its occurrence in lanolin, the waxy fat in wool. Although the principal component of lanolin is cholesterol, lanosterol is its precursor both in sheep and in all other animals. Cholesterol is in turn the precursor to other animal sterols. The cholesterol biosynthetic pathway also provides cells with a variety of important signaling molecules.1603... 

Sterols are widely distributed in both plants and animals. Many are of vital importance to animal physiology, such as cholesterol, the bile acids, vitamin D, sex hormones, and corticoid hormones. Many have value as medic-inals, such as the cardiac glycosides, hormones, and steroidal antibiotics. The occurrence and physiological properties of representative steroids are included in Table 30-2. 

Another complication is the possible interaction of inorganic sulfur species with A - and A -sterols. The occurrence of thiosteroids and of sulfur-bound steroid units in high-molecular-weight fractions of sediments and oils has been observed recently (15.16.20,26). The thiosteroids with the thiophene ring condensed to the D-ring almost exclusively possess the 140(H) configuration (26). Thiosteroids with a thiophene unit in the side chain mainly... 

Nichols, P.D., Palmisano, A.C., Rayner, M.S., Smith, GA., and White, D.C. (1990) Occurrence of novel C20 sterols in Antarctic sea ice diatom communities during spring bloom. Org. Geochem. 15, 503-508. 

Nishimura, M., and Koyama, T. (1977) The occurrence of stands in various living organisms and the behavior of sterols in contemporary sediments. Geochim. Cosmochim. Acta 41, 379-385. 

Dyas, L. and Goad, L.J. (1994) The occurrence of free and esterified sterols in the oil bodies isolated from maize seed scutella and a celery cell suspension culture. Plant Physiology and Biochemistry Paris 32(6), 799-805. 

Desbordes, S., Morin, O. and Prevot, A. (1983) Study of occurrence of brassicasterol in sunflower oil and variations in sterol composition of French sunflower seeds. Ann. Falsif. Exp. Chim. Toxicol., 76, 151-169. 

Radioactive carbon dioxide was detected in the breath of rats and men almost immediately after the administration, either orally or by injection, of (RS)-[5-14C]MVA,36 and up to 6.5% of the administered dose was exhaled within 100 minutes. Since the carbon dioxide was not derived from the unnatural S-enantiometer of MVA, or from degradation of cholesterol biosynthesized from the additive MVA, the observations support the hypothesis that there exists a metabolic shunt of intermediates of sterol biosynthesis which, although derived from MVA, do not lead to sterol formation. The significance of this shunt is that its occurrence could explain some of the human hypercholesterolaemias. The authors claim that MVA has no metabolic fate (hitherto known) except the biosynthesis of terpenoids is quite... 

The occurrence of cholesterol and related sterols in the membranes of eukaryotic cells has prompted many investigations of the effect of cholesterol on the thermotropic phase behavior of phospholipids (see References 23-25). Studies using calorimetric and other physical techniques have established that cholesterol can have profound effects on the physical properties of phospholipid bilayers and plays an important role in controlling the fluidity of biological membranes. Cholesterol induces an intermediate state in phospholipid molecules with which it interacts and, thus, increases the fluidity of the hydrocarbon chains below and decreases the fluidity above the gel-to-liquid-crystalline phase transition temperature. The reader should consult some recent reviews for a more detailed treatment of cholesterol incorporation on the structure and organization of lipid bilayers (23-25). 

Volkman J. K., Barrett S. M., Dunstan G. A., and Jeffrey S. W. (1993) Geochemical significance of the occurrence of dinosterol and other 4-methyl sterols in a marine diatom. Org. Geochem. 20, 7-15. 

Other Components of the Unsaponifiable Matter The unsaponifiable matter in a cmde regular sunflower oil is usually in the range of 0.5-1.5% (9, 17), or lower than 15 g/kg according to the Codex-Stan 210-1999. In addition to sterols (around 2.4. 6 g/kg) and tocopherols and tocotrienols (0.4-1.5 g/kg), there are minor components of sunflower oil. Aliphatic compounds and terpenoids occur naturally in oils. Of the terpenoid family, squalene is the most widely occurring compound. The occurrence of squalene in regular sunflower oil is fairly low 0.008-0.019% (5) or 15-20 mg/100 g (9). The aliphatic alcohol content is 100-mg/lOO-g oil (9). 

The sterol composition of both oils is compared in Table 12. Clearly, for HOSO, p-sitosterol is the sterol with the highest occurrence (42-70% of total sterols), followed by A7-stigmasterol (6.5-24%), campesterol (5-13%), and stigmasterol (4.5-13%). Although there are differences in the sterol composition of both oils, they are not large enough to enable easy analysis. 

Table 15 shows the sterol composition of mid-oleic sunflower oil according to the Proposed Draft Amendments to the Standard for Named Vegetable Oils (Report of the Eighteenth Session of the Codex Committee on Fats and Oils, London, 2003). Clearly, p-sitosterol is the sterol with the highest occurrence (56-58% of total sterols), followed by campesterol (9.1-9.6%) and stigmasterol (9.0-9.3%). p-sitosterol is the main sterol in aU three types of sunflower oil (regular, mid-oleic, and high-oleic). 

Tobacco leaf has a complicated chemical composition including a variety of polymers and small molecules. The small molecules from tobacco belong to numerous classes of compounds such as hydrocarbons, terpenes, alcohols, phenols, acids, aldehydes, ketones, quinones, esters, nitriles, sulfur compounds, carbohydrates, amino acids, alkaloids, sterols, isoprenoids [48], Amadori compounds, etc. Some of these compounds were studied by pyrolysis techniques. One example of pyrolytic study is that of cuticular wax of tobacco leaf (green and aged), which was studied by Py-GC/MS [49]. By pyrolysis, some portion of cuticular wax may remain undecomposed. The undecomposed waxes consist of eicosyl tetradecanoate, docosyl octadecanoate, etc. The molecules detected in the wax pyrolysates include hydrocarbons (Cz to C34 with a maximum of occurrence of iso-Czi, normal C31 and anti-iso-C32), alcohols (docosanol, eicosanol), acids (hexadecanoic, hexadecenoic, octadecanoic, etc ). The cuticular wax also contains terpenoids such as a- and p-8,13-duvatriene-1,3-diols. By pyrolysis, some of these compounds are not decomposed and others generate closely related products such as seco-cembranoids (5-isopropyl-8,12-dimethyl-3E,8E,12E,14-pentadecatrien-2-one, 3,7,13-trimethyl-10-isopropyl-2,6,11,13-tetradecatrien-1al) and manols. By pyrolysis, c/s-abienol, (12-Z)- -12,14-dien-8a-ol, generates mainly frans-neo-abienol. 

Bile alcohols are polyhydroxy C27 sterols that serve as intermediates in the biosjmthesis of cholic acid and chenodeoxycholic acid from cholesterol (1, 2). Recently several studies have shown that increased amounts of bile alcohols namely 27-nor-5p-cholestane-3a,7a,12a,24, 25-pentol and 5P-cholestane-3a, 7a,12a,25,26-pentol are excreted (as glucuronides in urine of patients with liver diseases such as primary biliary cirrhosis (3), liver cirrhosis (4, 5) and a-antitrypsin deficiency (6). Ichimiya et. al., described the occurrence of 5P-cholestane-3a,7a,12a,26,27-pentol (5P-cyprinol) and 5P-cholestane-3a,7a,... 

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