Yeast sterol

The active vitamins are produced by conversion of provitamins by ultraviolet light. Ergosterol, a yeast sterol, is converted to its active form, ergocalciferol (vitamin D2), and 7-dehydrocholesterol, which is found in many natural foods and is also synthesized in man, is converted to cholecalciferol (vitamin D3). Fish liver oils are virtually the only source of vitamin D3 in nature. The most active form of vitamin D3 is 1,25-dihydroxycholecalciferol and this is produced by the hydroxylation of cholecalciferol at position 25 in the liver and then at position 1 in the kidney. 

Moebius, F. F., Reiter, R. J., Hanner, M., Glossmann, H. High affinity of sigma rbinding sites for sterol isomerization inhibitors evidence for a pharmacological relationship with the yeast sterol C8-C7 isomerase, Brit. J. Pharmacol. 1997, 121, 1-6. 

Gachotte, D., C.A. Pierson, N.D. Lees, R. Barbuch, C. Koegel, and M. Bard (1997). A yeast sterol aux-otroph (erg25) is rescued by addition of azole anti-fimgals and reduced levels of heme. Proc. Natl. Acad. Sci. USA, 94, 11173-11178. 

The label was introduced into the sterol by base-catalyzed exchange with H20, or by incubating the GL-7 yeast sterol mutant or S. ferax with [ acetate in the presence and absence of tridemorph. 

Although the yeast sterol ergosterol (I) is at the present time not so cheap as diosgenin and its side-chain degradation to pregnane derivatives is more involved, it exhibits the marked advantage over all other readily available ring C unsubstituted steroids in that it already possesses the A -diene system, which in the other instances has first to be introduced. 

The two most commonly encountered yeast sterols are ergosterol and zymosterol other sterols e.g. lanosterol are also found in lesser amounts. 

These two C g molecules combine to yield the Cgg squalene in a reaction requiring the presence of molecular oxygen. Squalene is the precursor of the principal yeast sterols lanosterol, ergosterol and zymosterol. During fermentation, these compounds become esterified once wort oxygen has been utilized [75]. The formation of lanosterol is conducted by a mixed function... 

There is little evidence for the participation of cofactors or other activators in transmethylation reactions. An occasional methyltransferase has been found to be stabilized by mercaptoethanol or other sulfhydryl compounds and to be inhibited by p-chloromercuribenzoate (Mann and Mudd, 1963). A purified yeast sterol methyltransferase requires gluta-... 

ScHWENK, E., and G. J. Alexander Biogenesis of yeast sterols. II. Formation of ergosterol in yeast homogenates. Arch. Biochem. 76, 65 (1958). 

Rodriguez R J, Tkylor F R, Parks L W 1982 A requirement for ergosterol to permit growth of yeast sterol auxotrophs on cholestanol. Biochem Biophys Res Commun 106 435-441... 

Fig. 5 Schematic of the yeast sterol protein interaction network based on biochemical data and results of split-ubiquitin membrane yeast two-hybrid assays. The tethering protein, ERG28, is highlighted in red (Adapted from [52])...

Mo, C. and Bard, M. (2005) A systematic study of yeast sterol biosynthetic protein-protein interactions using the split-ubiquitin system. 

We investigated the ratio of free sterol to steryl ester in auxotrophic cells. Although the principal sterol of yeast is ergosterol, we have found that cholesterol can satisfy the sterol growth requirement of adapted yeast sterol auxotrophs and is readily esterified. We chose to use cholesterol for these experiments because of its stability against oxidative degradation and availability as a high purity radiolabeled compound. 

Plant P450obt.14DM displays a high degree of substrate specificity which is clearly distinct fix>m that of the animal and yeast sterol 14-demethylase [2,3]-... 

Rodriguez RJ, Parks LW. Structural and physiological features of sterols necessary to satisfy bulk membrane an sparldng requirements in yeast sterol auxotrophs. Arch Biochem Biophys 1983 225 861-871. 

Lanosterol has already been mentioned as a biosynthetic intermediate it is abundant in the wool fat of sheep. The related zymosterol, which lacks the three extra methyl groups, was first isolated from yeast. The most important yeast sterol, however, is ergosterol, a Cjs-steroid with three double bonds it is a provitamin D (see below). Plants contain several sterols with additional C substituents in the side chain, such as ergosterol has examples are stigmasterol and sitosterol. Insects are incapable of synthesizing the sterane skeleton they require sterols as essential food components. 

The first vitamin D was isolated from the irradiation of the yeast sterol ergosterol (Figure 2). This vitamin D was thought to be identical to that produced in the skin of animals and humans. However, studies revealed that when vitamin D produced from yeast was fed to chickens, they were unable to utilize it and developed rickets. When chickens were fed natural vitamin D from fish liver oil, rickets was prevented. This led to the conclusion that vitamin D originating from yeast was different from that in fish liver oil and animal and human skin. In 1937, this mystery was solved when the structure of provitamin D from pig skin was determined. A structural analysis revealed that provitamin D derived from ergosterol differed from that derived from pig skin. The provitamin D (ergosterol provitamin D2) that came from yeast had a double bond between carbons 22 and 23 and a methyl group on carbon 24. 

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