Sterols higher plant

Green algae Various A -, A - and A -sterols Higher plants p-Sitosterol, other A - and A -sterols... 

It is generally agreed that mevalonate is the precursor to sterols in higher plants as well as in animals and is also the precursor to plant carotenoids. However, it is poorly incorporated into monoterpenes and into some diterpenes such as those of the taxane group.26 27 The alternative glyceraldehyde 3-... 

Cholesterol 7 Animal fats Minor sterols of many higher plants >2.0 Mammary 1 HPA [35,37,47]... 

Sitosterol 33 Major sterol of most higher plants 1.8 Colon, Skin 1, CAR, ODC [20,30,44,50,128,129]... 

GREBENOK, R. J., GALBRAITH, D. W., DELLAPENNA, D, Characterization of Zea mays endosperm C-24 sterol methyltransferase One of two types of sterol methyltransferase in higher plants., Plant Mol.Biol., 1997,34, 891-896. 

Sterols are an important family of lipids, present in the majority of eukaryotic cells. Plant cells typically contain a mixture of sterols, such as P-sitosterol, stigmasterol, and 24-methylenecholesterol (Nabil and Cosson, 1996). Cholesterol is the most abundant of the free sterols found in sea water. Sterol content in chlorophyta is similar to higher plants, and also it contains large amount of cholesterol. Chondrus crispus (Irish moss), one of the red seaweeds harvested in quantity, has cholesterol as its major sterol. Fucosterol is the major sterol in brown algae. Rhodophyta species contain primarily cholesterol and to some extent desmosterol. Fucosterol, the dominant sterol in pheophyta, is apparently the major sterol of every species (Table 26.4). The brown seaweeds contain mainly fucosterol and fucosterol derivatives red seaweeds mainly... 

A24(25)-COmp0und, which is then reduced to give the saturated sterol side-chain. This route is further supported by a recent identification of stigmasta-7,24-dien-3/3-ol in higher plants.167 A similar pathway of alkylation operates for the biosynthesis of clionasterol [(24S)-(95)] from cycloartenol in the yellow-green alga Monodus subter-raneus, with the exception that direct reduction of a A24(28)-sterol [cf. (98)], rather than isomerization and then reduction, appears to occur.168... 

Is a specific Inhibitor of type II fatty acid synthetase In higher plants and . coll 12401. The acetyl-CoA ACP S-acety1-transferase Is the apparent specific site of Inhibition 12411. Another antibiotic, cerulenin (structure not shown) Inhbits -ketococy1-ACP synthetase I In bacteria, fungi, and plants, but also Is Inhibitory to other sites such as polyketide and sterol biosynthesis 1242-2441. Cerulenin and thiolactomycin Inhibited CQ14W-acetate Incorporation Into fatty acids at 150 values of 50 and 4 uM, respectively 12451. Recently cydohexanedlone herbicides have been shown to Inhibit lipid biosynthesis by Inhibition of acetyl-CoA carboxylase 12461. 

Figure 6.2 Proposed pathway for sterol biosynthesis in higher plants.

This enzyme catalyses the reduction of the A -double bond of the A -sterols into A -sterols in vertebrates and higher plants. A microsomal preparation from seedlings of Zea mays catalysed the NADPH-dependent reduction of the A -bond of A -cholestadienol, providing the first in vitro evidence for the intermediacy of A -sterols in plant sterol biosynthesis (Taton and Rahier, 1996). The potent inhibition of the enzyme by ammonium-containing fungicides suggests a cationic mechanism involved in this reduction reaction (Taton and Rahier, 1991). 

Taton, M., Benveniste, P. and Rahier, A. (1989) Microsomal sterol 14-reductase in higher plants. Characterization and inhibition by analogues of a presumptive car-bocationic intermediate of the reduction reaction. Eur.. Biochem., 185, 605-14. 

Taton, M. and Rahier, A. (1996) Plant sterol biosynthesis identification and characterization of higher plant A 7-sterol C5(6)-desaturase. Arch. Biochem. Biophys., 325, 279-88. 

Figure 6 Isoprenoids from bacteria (bacteriohopanepolyols, 20 pentalenolactone, 21 ubiquinone, 22 menaquinone, 23) and from higher plants (phytol, 24 p-carotene, 25 ginkgolide, 26 sterols, 27).

Sterols with the stigmastane skeleton (C29) (66c) typically occur in higher plants (Volkman, 1986), but are also the major sterols in many microalgae, such as several freshwater eustigmatophytes and chrysophytes, and green algae of the class Chlorophyceae. Unfortunately, the C27 to C29 desmethylsteranes are not characteristic for any specific taxon, because the precursors are widely distributed in the domain Eukarya. Even related species within the same class may contain major sterols with different carbon numbers or even mixmres of all three carbon skeletons (Volkman, 1986, 2003, 1980). 

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