Phosphatidylserine structure

Draw the structures of (a) all the possible triacylglycerols that can be formed from glycerol with stearic and arachidonic acid, and (b) all the phosphatidylserine isomers that can be formed from palmitic and linolenic acids. 

Most probably the presence of pardaxin pores alters the structure of the bilayer resulting in aggregation of phosphatidylserine vesicles mediated by contact but not by partial merging of their membranes. 

Cocco, L., Martelli, A., Billi, A., Matteucci, A., Vitale, M., Neri, L., and Manzoli, F. (1986) Changes in nucleosome structure and histone H3 accessibility. Iodoacetamidofluorescein labeling after treatment with phosphatidylserine vesicles. Exp. Cell Res. 166, 465 174. 

Fig. 1.9 Structures of charge neutral (phosphatidylcholine) and acidic (phosphatidylserine) phospholipids together with the moderately lipophilic and basic drug chlorphentermine. The groupings R1 and R2 refer to the acyl chains of the lipid portions.

Figure 21-5 A more complete outline of the biosynthesis of triacylglycerols, glycolipids, and phospholipids including characteristic eukaryotic pathways. Green lines indicate pathways utilized by both bacteria and eukaryotes. Structures of some of the compounds are shown in Fig. 21-4. The gray arrows show the formation of phosphatidylserine by exchange with ethano-lamine (Eq. 21-10).

Lipid synthesis is unique in that it is almost exclusively localized to the surface of membrane structures. The reason for this restriction is the amphipathic nature of the lipid molecules. Phospholipids are biosynthesized by acylation of either glycerol-3-phosphate or dihydroxyacetone phosphate to form phosphatidic acid. This central intermediate can be converted into phospholipids by two different pathways. In one of these, phosphatidic acid reacts with CTP to yield CDP-diacylglycerol, which in bacteria is converted to phosphatidylserine, phosphatidylglycerol, or diphos-... 

Fig. 25 (a) DNA release from EDOPC-DNA lipoplexes after addition of negatively charged lipid dispersion, as monitored by FRET (CM, oleic acid DOPA, dioleoyl phosphatidic acid DOPG, dioleoyl phosphatidylglycerol CL, cardiolipin DOPS, dioleoyl phosphatidylserine PI, phospha-tidylinositol). (b) Fraction of released DNA from EDOPC lipoplexes 10 min after addition of the respective anionic liposomes (c) X-ray diffraction patterns of mixtures of EDOPC and anionic liposome dispersions the respective structures are shown schematically on the left side (reproduced with permission from [98] copyright (2004) Biophysical Society)... 

Fig. 5.20 Changes in drug proton relaxation rate (1 /T2) as a function of increasing concentration of bovine brain phosphatidylserine (BBPS) alone and after addition of CaCI2- The spin systems measured are indicated by arrows on the drug structures. (Reprinted from Fig. 6 of ref. 117 with permission from Bertelsmann-Springer.)...

The following description of the isolation, purification and structure proof of a naturally occurring phosphatidylserine will be treated in exactly the same manner as with the previous phosphoglycerides. The methodologies described here can be used with any cell type and can be adapted for nearly any size sample. The exception, of course, would be if interest centered on the possible role of phosphatidylserine in a specific cellular reaction. Usually this would involve a small cell sample, and hence radioactive tracers would be needed. However, the biochemical pattern can be followed easily using exactly the same techniques. 

Assuming at this point that a highly purified sample of phosphatidylserine has been obtained from a specific biological source, structural chracterization of this preparation can be undertaken with ease and confidence. Prior to delving into the latter topic, a few general comments are appropriate at this time. 

Optical Rotation. A reasonable approach to the definition of the stereochemistry of the naturally occurring phosphatidylserine is to compare its optical activity with that of a known stereochemical structure. A synthetic sn-3 distearoylphosphatidylserine has an [a]g5 of 16.2, whereas a naturally occurring PS sample (e.g., obtained from human platelets) has an [a] 5 of 15.8. This observation would support an sn-3 configuration for the naturally-ocurring material. 

Huang, H.W., Goldberg, E.M. andZidovetzki, R., 1999, Ceramides modulate protein kinase C activity and perturb the structure of Phosphatidylcholine/Phosphatidylserine bilayers. Biophys. J. 77 1489-1497... 

Kiyono, K., Miura, K., Kushima, Y., Hikiji, T., Fukushima, M., Shibuya, I., and Ohta, A., 1987, Primary structure and product characterization of the Saccharomyces cerevisiae CHOI gene that encodes phosphatidylserine synthase. J. Biochem. 102 1089-1100. 

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