Phospatidic acid

A series of iomeprol-containing liposomes were evaluated in animals by Petersein et al. [62] and in healthy volunteers by Spinazzi et al. [63,64]. BR2 and BR21 are liposomes made of phosphatidyl choline (PC),dipalmitoyl phospatidic acid (DPPA) and cholesterol at a molar ratio of 2 1 (PC -i- DPPA/cholesterol) with an iodine content of 260 mg mL (BR2) and 320 mg mL" (BR21), respectively, and a size of 0.4 pm. BR2 contains 40 mg lipid mL and BR21 20 mg mL L In rabbits, BR2 tended to provide a higher and more persistent CT enhancement than BR21. 

Although not shown in the following simplified scheme, the phospatidic acid/ 1,2-diacylglycerol duo is also an intermediate in the pathway to the phospholipids (phosphatidylcholines, phosphatidylethanolamines, phosphatidylinositols, phospha-tidylinositols, and phosphatidylserines) and the mono- and digalactosyldiacylgly-cerols. 

Therraodjmamics of phospholipids depend on their molecular structure the conformation and the geometry of the phospholipids polar head, the orientation of the molecular backbone (glycerol in the case of glycerophospholipids) and the acyl-chaiiis orientation. NMR spectroscopy has been used extensively in order to reveal the lipid orientation in membrane structures [20]. NMR experiments have shown that except for phospatidic acid, in all phospholipid crystal structures a part of the sn-2 fatty acyl chain is parallel to the bilaycr surface. In egg phosphatidylcholines for example the averege size of the sn-2 acyl chain is 18 carbons while the sn- fatty acid is 16 carbons long. The final configuration of the two fatty acyl chains extends to the same depth from the bilayer surface and a thermodynamicaly stable conformation of the acyl lipid chains is formed [21]. 

While phosphatidylcholine and phosphatidylethanolamine are truly amphoteric, phosphatides such as phosphatidylinositol are anionic. These are most efficiently separated into their components by reversed-phase HPLC with an ion pairing agent (210,211). This is also true of the phospatide hydrolysis product, phosphatidic acid [RCOOCH2CH(OOCROCH20P03H]. Total free phospatidic acid may be determined by normal phase HPLC, but the acid can only be further characterized by reversed-phase chromatography after formation of esters such as the methyl ester (212). 

Another aspect of heating soybeans in particular is the impact on the phospholipase enzyme. The phospholipase enzyme is activated at approximately 55°C and remains activated up to approximately 100°C. In this temperature range, and with sufficient exposed surface area and time, the phospholipase enzyme modifies a portion of the phospatides in the oil fraction by splitting off the non-fatty acid moiety (16). The resultant calcium and magnesium salts of phosphatidic acids that are formed tend to be more oil-soluble than water-soluble, thereby converting phospatides from a hydratable form to a nonhydratable form (16). This has a resultant impact on the quantities of acid, caustic and silica needed to reduce the phosphorus content of the soybean oil in the downstream degumming and refining unit operations. 

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See also in sourсe #XX -- [ , ]

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