Monounsaturate oleate

Soybean oil contains about 21% of the monounsaturate oleate. Studies have shown that the oxidation rate of oleate is much slower than that of the polyunsam-rates, linoleate and linolenate, which oxidize quickly and are the major contributors to the poor stability of soybean oil (287, 323). A diet high in monounsaturates may help to reduce elevated levels of total plasma cholesterol without reducing the high-density lipoprotein-cholesterol level (324). Therefore, high-oleate soybean oil is not only more stable than conventional soybean oil (275), but also has enhanced nutritive value. 

The ability of titanium-grafted silicas in catalyzing the epoxidation with TBHP of fatty compounds was first tested on two pure Qg monounsaturated FAMEs methyl oleate (ds-9-octadecenoate Scheme 12.1) and methyl elaidate (trans-9-octadecenoate) [49]. In both cases, selectivity to 9,10-epoxystearate was very high (>95%) and the reaction was fully stereospecific, confirming that epoxidation with titanium catalysts and TBHP proceeds via a non-radical mechanism with retention of configuration at the C=C bond. Ti-MCM-41 was more active than Ti-SiC>2 (Fig. 12.1). Actually, methyl oleate was almost completely converted after... 

For all these reasons, the monounsaturated methyl oleate and methyl palmitoleate (C16 l) have been identified as the ideal components of biodiesel [41]. 

The salts of fatty acids (not naturally occurring) have long been known to have insecticidal properties. The most effective potassium salts center around oleate in the monounsaturated and saturated series, although potassium caprate (Cio) was especially active against Choristoneura occidentalis (Western spruce budworm) and Acleris gloverana (Western blackheaded budworm) (117). 

FIGURE 21-12 Routes of synthesis of other fatty acids. Palmitate is the precursor of stearate and ionger-chain saturated fatty acids, as well as the monounsaturated acids palmitoleate and oleate. Mammals cannot convert oleate to linoleate or a-linolenate (shaded pink), which are therefore required in the diet as essential fatty acids. Conversion of linoleate to other polyunsaturated fatty acids and eicosanoids is outlined. Unsaturated fatty acids are symbolized by indicating the number of carbons and the number and position of the double bonds, as in Table 10-1. 

Palmitate and stearate serve as precursors of the two most common monounsaturated fatty acids of animal tissues palmitoleate, 16 1(A9), and oleate, 18 1(A9) both of these fatty acids have a single cis double bond between C-9 and C-10 (see Table 10-1). The double bond is introduced into the fatty acid chain by an oxidative reaction catalyzed by fatty acyl-CoA desatu-rase (Fig. 21-13), a mixed-function oxidase (Box 21-1). Two different substrates, the fatty acid and NADH or NADPH, simultaneously undergo two-electron... 

The released unesterified cholesterol can then be usedfor membrane biosynthesis. Alternatively, it can be reesterified for storage inside the cell. In fact, free cholesterol activates acyl CoA cholesterol acyltransferase (ACAT), the enzyme catalyzing this reaction. Reesterified cholesterol contains mainly oleate and palmitoleate, which are monounsaturated fatty acids, in contrast with the cholesterol esters in LDL, which are rich in linoleate, a polyunsaturated fatty acid (see Table 24.1). It is imperative that the cholesterol be reesterified. High concentrations of unesterified cholesterol disrupt the integrity of cell membranes. 

The ready hydrogenation and isomerization of methyl oleate and palmitoleate with Fe(CO)s confirm the results of Ogata and Misono (18) with monounsaturated aliphatic compounds. In the isomerization of monoolefins Manuel (15) suggested the occurrence of equilibria involving either 7r-olefin HFe(CO)3 and a-alkyl Fe(CO)3 complexes, or TT-olefin Fe(CO)3 and 7r-allyl HFe(CO)3 complexes. The formation of olefin-iron tetracarbonyl complexes has been reported (19). The reaction of butadiene and Fe2(CO)9 has been observed to lead to the formation of butadiene-Fe(CO)4 and butadiene-[Fe(CO)4]2 complexes in which one or both double bonds are pi-bonded to the iron (16). A mechanism involving both monoene-Fe(CO)4 (I) and allyl-HFe(CO)3 complexes (II) is postulated for the isomerization of methyl oleate (Scheme II) and for its homogeneous hydrogenation. 

Oleate is an abundant 18-carbon monounsaturated fatty acid with a cis double bond between C-9 and C-10 (denoted A ). In the first step of oxidation, oleate is converted to oleoyl-CoA and, like the saturated fatty acids, enters the mitochondrial matrix via the carnitine shuttle (Fig. 17-6). Oleoyl-CoA then undergoes three passes through the fatty acid oxidation cycle to yield three molecules of acetyl-CoA and the coenzyme A ester of a A, 12-carbon unsaturated fatty acid, cis-A -dodecenoyl-CoA (Fig. 17-9). This product cannot serve as a substrate for enoyl-CoA hydratase, which acts only on trans double bonds. The auxiliary enzyme A, A -enoyl-CoA isomerase isomerizes the ci5-A -enoyl-CoA to the fra/J5-A -enoyl-CoA, which is converted by enoyl-CoA hydratase into the corresponding L-/3-hydroxyacyl-CoA (fra/75-A -dodecenoyl-CoA). This intermediate is now acted upon by the remaining enzymes of /3 oxidation to yield acetyl-CoA and the coenzyme A ester of a 10-carbon saturated fatty acid, decanoyl-CoA. The latter undergoes four more passes through the pathway to yield five more molecules of acetyl-CoA. Altogether, nine acetyl-CoAs are produced from one molecule of the 18-carbon oleate. 

Fig. 1.6. Structure of a triacylglycerol. Paknitate and stearate are saturated fatty acids, i.e., they have no double bonds. Oleate is monounsaturated (one double bond). Pol5mnsaturated fatty acids have more than one double bond.

The most common dietary fatty acids are the saturated long-chain fatty acids palmitate (C16) and stearate (C18), the monounsaturated fatty acid oleate (C18 l), and the polyunsaturated essential fatty acid, linoleate (C18 2) (To review fatty acid nomenclature, consult Chapter 5). Animal fat contains principally saturated and monounsaturated long-chain fatty acids, whereas vegetable oils contain linoleate and some longer-chain and polyunsaturated fatty acids. They also contain smaller amounts of branched-chain and odd-chain-length fatty acids. Medium-chain-length fatty acids are present principally in dairy fat (e.g., milk and butter), maternal milk, and vegetable oils. 

Ethyl oleate n. C2H5OOCC17H33. This monounsaturated fatty ester is a solvent, lubricant, and plasticizer. 

The results presented above show that active E. coli CPFA synthase can be expressed in plants. Since no specific targeting sequence was used, the enzyme is presumed to have interacted with oleate moieties in membranes accessible to the cytoplasm. Although not an integral membrane protein, the synthase is normally associated with membranes in the bacterium and is active on monounsaturated vesicles in vitro [3]. 

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