Phosphatidylcholine synthetic

B) tobacco phosphatidylcholine ( ), synthetic dioleate phosphatidylcholine ( ), tobacco phosphatidylethanolamine ( ), synthetic dipalmitate phosphatidylethanolamine (O), digalactosyldiacylglycerol ( ), tobacco PG as control ( A ). ... 

The presence of impurities like free fatty acids in egg or soybean phosphatidylcholine, or in the (semi)synthetic phosphatidylcholines (e.g., DMPC, DPPC, DSPC) can be detected by monitoring the electrophoretic behavior of liposome dispersions of these phospholipids in aqueous media with low ionic strength a negative charge will be found on these liposomes when free fatty acids are present in the bilayers. 

There is also inside-outside (transverse) asymmetry of the phospholipids. The choline-containing phospholipids (phosphatidylcholine and sphingomyelin) are located mainly in the outer molecular layer the aminophospholipids (phosphatidylserine and phos-phatidylethanolamine) are preferentially located in the inner leaflet. Obviously, if this asymmetry is to exist at all, there must be limited transverse mobility (flip-flop) of the membrane phospholipids. In fact, phospholipids in synthetic bilayers exhibit an extraordinarily slow rate of flip-flop the half-life of the asymmetry can be measured in several weeks. However, when certain membrane proteins such as the erythrocyte protein gly-cophorin are inserted artificially into synthetic bilayers, the frequency of phospholipid flip-flop may increase as much as 100-fold. 

The second synthetic route involves activation of an alcohol (for example, choline) to produce CDP-choline. The latter participates in the transfer of choline onto diglyceride to form phosphatidylcholine. 

The 2-anthroyl fluorophore can be incorporated synthetically in phosphatidylcholine vesicles (anthroyl-PC), which provides an elegant tool for investigating the bilayers of egg phosphatidylcholine vesicles (Perochon et al., 1992). 

Lipid-protein interactions are of major importance in the structural and dynamic properties of biological membranes. Fluorescent probes can provide much information on these interactions. For example, van Paridon et al.a) used a synthetic derivative of phosphatidylinositol (PI) with a ris-parinaric acid (see formula in Figure 8.4) covalently linked on the sn-2 position for probing phospholipid vesicles and biological membranes. The emission anisotropy decays of this 2-parinaroyl-phosphatidylinositol (PPI) probe incorporated into vesicles consisting of phosphatidylcholine (PC) (with a fraction of 5 mol % of PI) and into acetylcholine receptor rich membranes from Torpedo marmorata are shown in Figure B8.3.1. 

Figure 1. Synthetic pathway for PS and PE in mammalian cells. The major steps occuring in the synthesis and interconversion of PS and PE are shown. The PS synthases condense serine with a phosphatidyl moiety derived from PC and PE. The nascent PS can be converted to PE by decarboxylation. PE can also be formed by transfer of a phosphoethanolamine moiety from CDP-ethanolamine to diacylglycerol via the Kennedy pathway. The abbreviations used are PC, phosphatidylcholine PS, phosphatidylserine PE, phosphatidylethanolamine DG, diacylglycerol PSD, phosphatidylserine decarboxylase PSS, PS synthase.

LEH is primarily composed of a combination of saturated high-carbon phospholipids and cholesterol. Synthetic phospholipids replaced hydrogenated soy lecithin when the latter was found to induce several untoward biological responses (40). Current choice of a saturated high-carbon phospholipid is mostly between distearoyl phosphatidylcholine (DSPC, 55°C) and... 

Figure 4 Design of a chemically defined diepitope liposomal anticancer vaccine. Small unilamellar liposomes (PC/PG/Chol 75/20/50 molar ratio diameter 65nm) containing 5mol% of the synthetic thiol-reactive lipopeptide adjuvant anchor Pam3CSS-Mal were reacted, at 25°C and pH 6.5, with equimolar quantities of the peptides ErbB2 (p63-71), derivatized with a CG linker at its N-terminus, and HA307-319, derivatized with a C-linker at its C-terminus. Abbreviations PC, phosphatidylcholine PE, phosphatidylethanolamine SUV, small unilamellar vesicles. Source From Refs. 11, 74.

Parente RA, Nir S, Szoka FC Jr. pH-dependent fusion of phosphatidylcholine small vesicles. Induction by a synthetic amphipathic peptide. J Biol Chem 1988 263 4724 730. 

Phosphatidylcholine There are three sequential reactions in this synthetic pathway ... 

Fig. 21-5, are also used for formation of both phosphatidylcholine and phosphatidylethanolamine. In both cases, the free base, choline, or ethanolamine180a b is phosphorylated with ATP. Choline phosphate formed in this manner is then converted by reaction with CTP to CDP-choline (Eq. 17-58).181 Phosphatidylcholine is formed from this intermediate1813/b while CDP-ethanolamine is used to form phosphatidylethanolamine (Fig. 21-5). These synthetic reactions occur within cell nuclei as well as on surfaces of cytoplasmic membranes.1810...

We have now extended these studies to synthetic phospholipids that contain short chain fatty acyl groups and which are water soluble, such as dibutyryl and dihexanoyl phosphatidylcholine (PC). These phospholipids are monomeric below their critical micelle concentration (cmc), yet activate the enzyme. In order to carry out kinetic studies, the long chain phospholipid substrate must generally be solubilized by a detergent such as Triton X-100 which serves as an inert matrix. Further understanding of the mechanism of the activation by short-chain phospholipids requires first a quantitation of the solubilization of these compounds by detergent ... 

The influence of substituent size, polarity, and location on the thermotropic properties of synthetic phosphatidylcholines has been studied by Menger et al. [18], The effect of increasing membrane curvature on the phase transition has been investigated by DSC and FTIR [19]. In addition, a data bank, LIPIDAT, on lipid phase transition temperatures and enthalpy changes is available [20, 21],... 

LCAT, whereas LCAT activity with HDL2 as a substrate is minimal. Others have confirmed that HDL3 is a better substrate for LCAT than HDL2 (Bll, M28). Hamilton et al. (H5) noted that nascent disk-shaped HDL secreted by rat liver were better substrates for LCAT than mature spherical HDL isolated from plasma. Synthetic discoidal complexes of apoA-I, phosphatidylcholine, and cholesterol were better substrates for LCAT than unilamellar vesicles of phosphatidylcholine and cholesterol, incubated in the presence of apoA-I (M32). 

M32. Matz, C. E., and Jonas, A., Reaction of human lecithin cholesterol acyltransferase with synthetic micellar complexes of apolipoprotein A-I, phosphatidylcholine and cholesterol. ]. Biol. Chem. 257, 4541-4546 (1982). 

In the following section, emphasis will be placed on establishing the placement of the fatty acyl chains on the glycerol backbone by a combination of enzymological maneuvers and organic synthetic chemistry. At the same time the stereochemical configuration of the phosphatidylcholine will be developed. It is hoped that the reasons for these choices will become self-evident. 

As mentioned in an earlier section, there are no chemical reagents that can establish with any certainty the specific position of attachment of an acyl ester on a diacylphosphatidylcholine or any other phosphoglyceride. The same is true in any attempt to establish the stereochemical conformation of phosphatidylcholine, whether sn-1 or sn-3, by strictly chemical means. The solution to this dilemma is to use synthetic phosphoglycerides of defined structure as well as phospholipase A2 to establish the correct stereospecificity of the latter enzyme. Certainly, this is reminiscent of the chicken or egg argument, yet it does work as will be explained below. 

Synthetic Schemes. There are basically two main routes to preparation of mixed acid (enantiomeric) diacylphosphatidylcholines. The first involves a total de novo synthesis and the second centers on a partial or semisynthesis using a highly purified naturally occurring phosphatidylcholine as starting material. Both approaches have merits and drawbacks, which are noted as follows. 

Usefulness of the Above Synthetic Products. The mixed acid phosphatidylcholines obtained by the above synthetic procedures can be used to support (in part) the specificity of positioning of the fatty acyl residues on these phosphoglycerides and the specificity of attack by phospholipase A2. As a test of these two propositions, incubation of these two species of mixed acid phosphoglycerides with phospholipase A2 will yield the products given in Figure 4-12. 

Phospholipase A2 Action. As in the case of phosphatidylcholine, the above-mentioned phospholipases will attack only the sn-3 form of naturally occurring (as well as synthetic) phosphatidylethanolamine. The products are, of course, lysophosphatidylethanolamine (1 -6>-acyl-2-lyso-.rn-glycero-3-phosphoethanolamine) and the fatty acids (liberated from the sn-2 position). The latter can be analyzed for composition and structure, as the methyl esters, by gas-liquid chromatography coupled with mass spectrometry. Usually these acyl groups are largely the unsaturated types. 

Two model peptides—alamethicin which is a-helix peptaibol-transmembrane antimicrobial peptide (AMP) and synthetic a-helix alanine-rich peptide (K3A18K3)—inserted into l,2-dimyristoyl-sn-glycero-3-phosphatidylcholine... 

Figure 6. Single-channel currents of synthetic PHB96. Left Representative current fluctuations obtained when the given voltage was applied at a planar bilayer made from 1-palmitoyl, 2-oleoyl, phosphatidylcholine (16 0,18 1, PC) containing0.1 to 1% of 96mer of PHB between symmetric solutions of 60 mM RbCI, 5 mM MgCh, 10 mM Hepes CsOH, pH 7.2. The solid horizontal bar in each record indicates the current level with the channel closed. pO is the probability that the channel is in the open state. Right Corresponding conductivity histograms. N indicates the total number of observations that have been analyzed.

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