Palmitic acid esterified

Here R, and R2 are long, fatty acid side chains. The parent fatty acids RjC02H and R2C02H usually have an even number of carbon atoms 16- and 18-carbon acids are the most common. The acid esterified to the hydroxyl group on C-l of the glycerol (that at the top of phosphatidylcholine is drawn above) usually has a fully saturated chain, whereas the acid attached at C-2 often has one or more double bonds, which are almost always cis double bonds. Table 17.1 lists some of the fatty acids commonly found in these positions. A phosphatidylcholine that has palmitic acid esterified at both the C-l and C-2 positions of the glycerol is known by... 

Although fatty acids are abundant in the body, only a small fraction is present as free fatty acids (FFA) by far the greater amount is found in the form of esters. The simple fatty acid esters are the glycerides and the waxes. In the waxes the fatty acids are esterified with long chain fatty alcohols contmning from 12 to 34 C atoms, for example beeswax is composed chiefly of palmitic acid esterified with myricyl ( 14) alcohol. 

This structure shows a triglyceride with three identical saturated fatty acids. Tripalmitin, in which all fatty acids are palmitic acid (n = 14), provides one example of a fat. Triolein is an oil containing only oleic acid moieties esterified to glycerol. In contrast to these two examples, it is by no means necessary that the three fatty acid groups be derived from only one fatty acid. For example, we might have a triglyceride that contains one saturated fatty acid, say palmitic acid, one monounsaturated fatty acid, say oleic acid, and one polyunsaturated fatty acid, perhaps arachidonic acid. 

Sodium, potassium, and calcium salts of ascorbic acids are called ascorbates and are used as food preservatives. These salts are also used as vitamin supplements. Ascorbic acid is water-soluble and sensitive to light, heat, and air. It passes out of the body readily. To make ascorbic acid fat-soluble, it can be esterified. Esters of ascorbic acid and acids, such as palmitic acid to form ascorbyl palmitate and stearic acid to form ascorbic stearate, are used as antioxidants in food, pharmaceuticals, and cosmetics. 

L-Ascorbic acid (Figure 10.8) proved to be less recalcitrant than glucose and could be esterified with palmitic acid in the presence of CaLB in [BMIm][BF4] and similar ionic liquids [116, 117]. The equilibrium was shifted toward the product by applying a vacuum to remove the water, and undesirable precipitation of the reaction product on the biocatalyst was obviated by the addition of a hydrophobic phase such as hexane or polypropylene beads [116]. 

As the chain length increases up to C,6 0, an increasing proportion is esterified at the sn-2 position this is more marked for human than for bovine milk fat, especially in the case of palmitic acid (C,6 0). 

As can be seen in Table 4.2, the fatty acids are not randomly distributed among the three positions of the TG in bovine milk. Control of esterification is not understood, but there are several factors known to affect it. The presence of glucose is known to stimulate the synthesis of milk TG (Dimmena and Emery 1981 Rao and Abraham 1975). In the mouse, Rao and Abraham concluded that glucose was supplying factors other than NADPH or acylglycerol precursors that stimulated milk fat synthesis. The fatty acid that is esterified is known to be affected by the concentration of the acyl donors present (Marshall and Knudsen 1980 Bickerstaffe and Annison 1971). However, in studies under various conditions, palmitic acid was consistently esterified at a greater rate than other fatty acids (Bauman and Davis 1974 Moore and Christie 1978 Smith and Abraham 1975). 

Over 100 fatty acids are known to occur naturally. They vary in chain length and degree of unsaturation. Nearly all have an even number of carbon atoms. Most consist of linear chains of carbon atoms, but a few have branched chains. Fatty acids occur in very low quantities in the free state and are found mostly in an esterified state as components of other lipids. The pKa of the carboxylic acid group is about 5, and under physiological conditions, this group will exist in an ionized state called an acylate ion e.g., the ion of palmitic acid is palmitate, CH3(CH2)i4COO". 

To measure the activity in acidolysis, triolein was esterified with equimolar amounts of palmitic acid at 60°C by means of immobilized lipase (Fig. 4). The incorporation of palmitic acid into the triolein is measured by GIC of fatty acid methyl esters obtained after methoxylation of the triglycerides (8,9). One Batch Interesterification Unit (BIU) corresponds to 1 /xmol of palmitic acid incorporated (initial activity) into triolein per min. 

Unlike many fats and oils, the cocoa butter used to make chocolate is remarkably uniform in composition. All triacylglycerols contain oleic acid esterified to the 2° OH group of glycerol, and either palmitic acid or stearic acid esterified to the 1 ° OH groups. Draw the structures of two possible triacylglycerols that compose cocoa butter. 

Plant waxes are usually found on leaves or seeds. Thus, cabbage leaf wax consists of the primary alcohols C12 and Cis—C28 esterified with palmitic acid and other acids. The dominant components are stearyl and ceryl alcohol (C26H53OH). In addition to primary alcohols, esters of secondary alcohols, for example, esters of nonacosane-15-ol, are present ... 

The atherogenicity of fats containing palmitic acid is higher when this fatty acid is esterified at the i 2-position than at the outer positions, even when cholesterole-mia is not affected (68). 

Retinol is esterified to palmitic acid in the intestinal mucosa and secreted as components of chylomicrons into the lymphatic system and through blood stored in liver. 

Fig. 4 Separation of dipalmitoyl phosphatidylcholine and distearoyl phosphatidylcholine. The solvent system used for the TC-CCC was hexane/ethyl acetate/ethanol/1% trifluoroacetic acid (5 5 5 4). The upper phase (organic phase) was mobile. The rotational speed was maintained at 1500-700 rpm. The highest column pressure was 360 psi. Amounts (100 pg each) of phosphatidylcholine dipalmitoyl and phosphatidylcholine distearoyl were loaded. Each fraction was spotted and developed on the HPTLC using chloroform/methanol/ 0.2% CaCl2 (60 32 4). Distearoyl phosphatidylcholine contains 2 mol of esterified stearic acids and dipalmitoyl phosphatidylcholine contains 2 mol of esterified palmitic acids. PC C16 0, dipalmitoyl phosphatidylcholine PC C18 0, distearoyl phosphatidylcholine. SF, solvent front.

To assess the ability of the TC-CCC molecular species, two molecular species of phosphatidylcholine, which were synthesized, were subjected to TC-CCC. Dipalmi-toyl phosphatidylcholine (PC C16 0) and distearoyl phosphatidylcholine (PC C18 0), two of the major molecular species of phosphatidylcholine, were completely separated as shown in Fig. 4. Distearoyl phosphatidylcholine contains 2 mol of esterified stearic acids and dipal-mitoyl phosphatidylcholine contains 2 mol of esterified palmitic acid. The structures of these compounds are shown in Fig. 4. These two compounds were completely separated. This result indicates that the TC-CCC system can separate molecular species in both phospholipids and glycolipids categories. 

The esters utilized oleic, palmitic, linoleic, stearic, palmitoleic, myristic, and laurlc acids, but collectively these lipophilic conjugates represented <0.1% of the applied dose. The hydroxyethyl groups of dlpyrldamol (a coronary vasodilator) and mopldamol (a cytostatic agent) are esterified with oleic and palmitic acids (35). These lipophilic derivatives of both drugs are excreted In feces (about 4X of the applied dose for rats and humans). 

Purdon D, Aral T, Rapoport SL No evidence for direct incorporation of esterified palmitic acid from plasma into brain lipids of awake adull rat. J Lipid Res 1997 38 526-530. 

Certain fatty acids (primarily myristic and palmitic acids) are covalently attached to a wide variety of eukaryotic proteins. Such proteins are referred to as acylated proteins. Fatty acid groups (called acyl groups) clearly facilitate the interactions between membrane proteins and their hydrophobic environment. Fatty acids are transported from fat cells to body cells esterified to serum proteins and enter cells via acyl transfer reactions. Some of the acylated proteins in cells... 

The provitamin A, /8-carotene, is cleaved in the enterocyte by a soluble oxygenase w hich requires bile salts for its activity [90]. The product, retinal, is reduced by another soluble enzyme to retinol which is esterified chiefly with palmitic acid by a microsomal enzyme, acyl-CoA retinol acyltransferase which is inhibited by taurocholate in vitro this enzyme is very similar to ACAT [91]. Since j8-carotene is taken up by the intestine and rather efficiently converted to retinyl esters which appear in lymph, it must be inferred that the cytosolic oxygenase is exposed to sufficiently high concentrations of bile salts for the cleavage to occur. 

---