The occurrence of sterols

If one specifies the differences between bacteria (prokaryotes) and higher organisms (eukaryotes), one point Is always mentioned. Higher organisms contain sterols whereas bacteria do not. Only a few exceptions are known for the occurrence of sterols In bacteria. 

M. Kalinowska and Z.A. Wojciechowski, The occurrence of sterol eater hydrolase activity in roots of white mustard seedlings. Phytochemistry 22 59 (1983)... 

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. 

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... 

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. 

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). 

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,... 

Alkan-1,15-diols and alkan-15-one-l-ols. The occurrence of long chain 1,15-diols (III) and alkan-15-one-l-oIs (IV) have been reported in the sterol and stand fractions of Black Sea Unit I and Unit II sediment extracts for the first time ( n). 

In considering the mechanism of action of azoles on sterol biosynthesis in powdery mildew (see figure 4), we should discuss a variation in the biosynthetic sequence to the end-product. The occurrence of obtusifoliol and 24-methylenedihydrolanosterol following azole treatment confirms that the oxidative removal of the C-14-methyl group by the cytochrome P-450 system is also inhibited. The fact that side chain alkylation is performed prior to this step in powdery mildew seems worthy of note, reflecting as it does a principal difference to cholesterol biosynthesis in mammals. 

After the discovery of the C26-sterols in marine planktons, all the marine Cje-sterols were suggested to have originated from a phytoplankton. The occurrence of 19-nor-C26-sterol in A. polypoides, probably originating from C26-sterol in the diet, suggests that one of the processes involved in the biosynthesis of these 19-nor-sterols could be the removal of the Cjo-methyl group from the substrates [13]. The sterols in Axinella verrucosa were found to consist of a mixture of unique stanols containing a 3)8-hydroxymethyl-A-nor-5a-cholestane (22) nucleus with conventional side chains [14]. Cholest-4-en-3-one was found to be an intermediate in the bioconversion of cholesterol into 3)8-hydroxymethyl-A-nor-5a-cholestane [15]. 

Conventional marine sterols have A -, A - or A Miene nuclei, but the occurrence of A -sterols was reported in Axinella cannabina [36]. Recently a complete analysis of sterols in the same species by Itoh et al. [37] showed the presence of 74 sterols with a variety of nuclei A , A, A , A, Sa-saturated and 5a-methoxy-... 

The occurrence of secosterols 59, and 60, in Pseudopterogorgia sp. appears to represent the first example of the 9,11-secosterols with the dinosterane skeleton. Furthermore, the side chain hydroxylation at C24 is very rare among marine sterols [41]. 

The bacterial genus Mycoplasma Is well known for the occurrence of and dependence on sterols [3], but these bacteria without cell walls do not synthesize their sterols by themselves [4]. Bacterial species which contain and synthesize sterols by themselves are Methylococcus capsulatus [5,6], Hannocystls exedens [7] and an L-form of Staphylococcus aureus [8]. It Is Interesting to note that Methylococcus capsulatus simultaneously contains hopanolds [6]. 

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