Choline-containing phosphatides

Figure 3. Biosynthesis of choline-containing phosphatides. Figures in parentheses refer to equations in...

Taurog and his associates (174) found that phosphatides are absorbed quantitatively from a petroleum ether solution by magnesium oxide 0.6 g. magnesium oxide suffices to absorb 0.85 mg. of phosphatide phosphorus dissolved in 15 ml. petroleum ether. Use of 1.75 g. magne.sium oxide is however preferable when choline-eontaining phosphatides have to be separated from non-choline-containing phosphatideS. The separation is based on the elution of the choline-containing phosphatides by methyl alcohol. 

The separation of choline-containing phosphatides from non-choline-containing phosphatides can however also be accomplished by first dissolving the phosphatides in methanol and then treating this methanol solution with magnesium oxide. The following procedure is used. 

Fig. 9. Effect of choline on specific activity - time curve of choline-containing (C.C.Ph.) and non-choline-containing phosphatide (N.C.C.Ph.) phosphorus of liver (45).

It can be seen from Figure 1 that the choline-containing phospholipids, phosphatidylcholine and sphingomyelin are localized predominantly in the outer monolayer of the plasma membrane. The aminophospholipids, conprising phosphatidylethanolamine and phosphatidylserine, by contrast, are enriched in the cytoplasmic leaflet of the membrane (Bretcher, 1972b Rothman and Lenard, 1977 Op den Kamp, 1979). The transmembrane distribution of the minor membrane lipid components has been determined by reaction with lipid-specific antibodies (Gascard et al, 1991) and lipid hydrolases (Biitikofer et al, 1990). Such studies have shown that phosphatidic acid, phosphatidylinositol and phosphatidylinositol-4,5-fc -phosphate all resemble phosphatidylethanolamine in that about 80% of the phospholipids are localized in the cytoplasmic leaflet of the membrane. 

Definition and example of a glycerophospho-lipid Phospholipids that contain glycerol are called glycerophospholipids or phosphoglyc-erides. All contain phosphatidic acid, the simplest glycerophospholipid. When an alcohol, such as choline, is esterified to phosphatidic acid, the product is phosphatidylcholine. 

In neutrophils, phosphatidic acid produced by PLD is then subsequently cleaved by phosphatidic acid phosphohydrolase [32]. In neu-tropohils, choline-containing phosphoglycerides contain approximately equal amounts of alkylacyl- and diacyl-glycerols. Thus the PA is dephos-phorylated to give both DAG and alkylacylglycerol. The DAG produced... 

Data obtained by a variety of methods show that in eukaryotic cells the choline containing phospholipids are preferentially localized in the outer leaflet of the bi-layer (707o and 807o for phosphatidylcholine and sphingomyelin, respectively) while phosphatidylinositol, phosphatidylserine and phosphatidic acid are concentrated in the inner leaflet (VERKLEIJ, 1973 RENOOJ... 

Further evidence in support of the decreased rate of phosphatide turnover in choline deficiency is provided by studies (27) in which choline containing was fed to both normal and choline-deficient animals. Incorporation of new choline (tagged by the presence of was found to be retarded in the choline-deficient rat. 

Three days after choline, containing N, had been administered, 21% or more of the choline present as phosphatide in the whole animal was found to be replaced by isotopic dietary choline. The corresponding replacement figure for labeled ethanolamine was 28% or more. The choline content of liver is renewed at the highest rate. Renewal of the choline of the gastrointestinal tract is slower than that in liver, slowest replacement takes place in the brain (170). 

Soya lecithin is a natural product which contains about 34% glycerides (soya oil), 5% sugars, and 61% phosphatides. The phosphatides in turn are comprised of phosphatidyl choline, i.e., chemical lecithin (20%), phosphatidyl ethanolamine (20%), and phosphatidyl inositol (21%). 

The nomenclature for associating individual fatty acid groups with particular phosphodig-lyceride derivatives is straightforward. For instance, a phosphatidic acid (PA) derivative which contains two myristic acid chains is commonly called dimyristoyl phosphatidic acid (DMPA). Likewise, a PC derivative containing two palmitate chains is called dipalmitoyl phosphatidyl choline (DPPC). Other phosphodiglyceride derivatives are similarly named. 

Amino acids, amino groups, amino sugars, and nucleic acid derivatives usually account for >95% of the organic N in soils (Anderson et al., 1989), and many other N-containing compounds have been reported in trace amounts (Stevenson, 1994). Anderson et al. (1989) have found traces of L-phosphatidic acid, choline, ethanol-amine, and uric acid (the end product of N metabolism of many animals), which can be oxidized to allantoin, cyanuric acid, and urea. 

In the work-up of the diethyl ether reaction, the solvent is removed (in a hood) under a stream of nitrogen. Then the ether-free aqueous dispersion is mixed with 10 ml of a 5 mM EDTA solution to bind the calcium ions. Without the latter treatment, the calcium salt of the phosphatidic acid cannot be recovered (easily) from the reaction mixture. Thus, subsequent to the EDTA treatment, the sample is mixed with sufficient chloroform and methanol to make a mixture of chloroform-methanol-water (1 2 0.8, v/v). Then 0.5 volume chloroform and 0.5 volume water are added, and the mixture is vigorously shaken for 1 min and then allowed to separate into two phases. The upper, water-rich phase contains free nitrogen base—in this case, choline. It can be analyzed by the techniques described earlier. 

It is a complex mixture of acetone-insoluble phosphatides that consists chiefly of phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl inositol combined with various amounts of other substances such as triglycerides, fatty acids, and carbohydrates. Refined grades of Lecithin may contain any of these components in varying proportions and combinations depending on the type of fractionation used. In its oil-free form, the preponderance of triglycerides and fatty acids is removed and the product contains 90% or more of phosphatides representing ah or certain fractions of the total phosphatide complex. Edible diluents, such as cocoa butter and vegetable oils, often replace soybean oil to improve functional and flavor characteristics. Lecithin is only partially soluble in water, but it readily hydrates to form emulsions. The oil-free phosphatides are soluble in fatty acids, but they are practically insoluble in fixed oils. When ah phosphatide fractions are present, Lecithin is partially soluble in alcohol and practically insoluble in acetone. 

Plasmalogens are phospholipids containing an a,P-unsaturated ether at C-1. Phosphatidal choline, the plasmalogen corresponding to phosphatidyl choline, is formed by desaturation of a 1-alkyl precursor. 

Lecithin, a mixture of phosphatidyl choline, phosphaddyl ethanolamine, and phosphatidyl inositol, is used as a surfactant in many food, pharmaceutical, and cosmetic products. Lecithin is a product of soy bean oil degumming operations. It is obtained from the hexane extract of flaked soy beans which contains the seed oil and a portion of the phosphatides that are initially present in the soy bean membrane. The exhact is seated with water at 80 °C, and the phosphatides are hydrated rendering them oil insoluble which makes it easy to filler them from the oil. This oil insoluble fraction is termed cmde lecithin and consists of about 70% phosphatides and 30% oil. De-oiled lecithin is obtained by treating the cmde lecithin with acetone. Lecithin is insoluble in acetone and the oil is, and a separation into a 90 to 9r phosphatides fraction can be achieved quite readily. The prior... 

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