Occurrence of phosphatidylsulfocholine, the sulfonium analog of phosphatidylcholine in some diatoms and algae.

A survey of seven species of diatoms, one Euglena sp. and one dinoflagellate sp. for the presence of phosphatidylsulfocholine (PSC), the sulfonium analog of phosphatidylcholine (PC), was carried out using 1H-NMR spectroscopy and ammonia desorption chemical ionization mass spectrometry. PSC alone was found only in a non-photosynthetic diatom, Nitzschia alba. PSC, together with PC, was found in four of the diatoms (Nitzschia angularis, Cylindrotheca fusiformis, Phaeodactylum tricornutum and Navicula pelliculosa) in proportions of 6-24% of the total PC + PSC fraction, but little or no PSC (less than 2%) was detected in the remaining two (Cyclotella nana and Navicula incerta). Little or no PSC (less than 2%) was detected in a Euglena sp. by 1H-NMR but its presence was confirmed by 35S-labeling. The amount of PSC, if any, in the dinoflagellate (Amphidinium carterae) was below the level of detection by 1H-NMR.

Phosphatidylsulfocholine bilayers. An infrared spectroscopic characterization of the polymorphic phase behavior.

The thermal response of aqueous dispersions of phosphatidylsulfocholines (dimyristoyl-, dipalmitoyl- and distearoyl-) was studied by Fourier transform infrared spectroscopy. Comparison with that of the corresponding phosphatidylcholines showed several close resemblances, including the observation in the gel phase of a "pretransition" and of a "subtransition". The similarity in the thermotropic phase behavior of these two lipid classes is consistent with the total replacement of phosphatidylcholine by phosphatidylsulfocholine in certain marine diatoms.

[Can phosphatidyl sulfocholine, the sulfonium analog of lecithin, efficiently replace lecithin in natural membranes?]. / L'analogue sulfonium de la lécithine, le phosphatidyl sulfocholine, peut-il remplacer efficacement la lécithine dans les membranes naturelles?

Lecithin does not exist in the marine diatom, Nitzschia alba, being completely replaced by phosphatidylsulfocholine (PSC), the sulfonium analogue of phosphatidylcholine (PC). Thus, the question arises: how can PSC effectively replace lecithin in a natural membrane? We have compared the physical properties of a homologous series of synthetic PSC's (di - 14:0, di- 16:0, di- 18:0, di 18:1) in aqueous dispersion with those of a similar series of PC's. The PSC's formed liposomes having similar properties to those of the PC's. However, the saturated PSC homologues showed main transition temperatures 2-4 degrees C above those of the corresponding PC's as measured by differential scanning calorimetry, fluorescence polarization or electron paramagnetic resonance. Furthermore, there was no significant difference between the two types of membranes with respect to their permeability to urea or 6-carboxyfluorescein either in the presence or absence of cholesterol. We have also shown that yeast cells can grow and survive in spite of a complete replacement of PC by PSC in their membranes. The sulfonium analogue of lecithin would appear to be able to replace PC in natural membranes because of the similarity in their physical properties.

Chemical synthesis of sn-3-phosphatidyl sulfocholine, a sulfonium analog of lecithin.

A sulfonium analog of lecithin has been reported to replace the ubiquitous phosphatidyl choline in a non-photosynthetic diatom, Nitzschia alba. The structure of this sulfonium analog has now been established by chemical synthesis using the following methods: (i) condensation of sn-3-phosphatidic acid (dimyristoyl-, dipalmitoyl-, distearoyl-, distearoyl-, and dioleoyl-) with sulfocholine chloride in the presence of triisopropylbenzenesulfonylchloride in chloroform-pyridine (9:1); and (ii) phosphorylation of 1,2-dipalmitoyl-sn-glycerol with monophenylphosphoryl-dichloridate followed by a reaction with sulfocholine in the presence of pyridine and finally removal of the blocking phenyl group by catalytic hydrogenolysis. The desired synthetic products were obtained in overall yields of 50-70% and 11% for methods (i) and (ii), respectively, and were characterized by elemental analyses; infrared spectroscopy, nuclear magnetic resonance spectrometry, and mass spectrometry; optical rotation; and thin-layer chromatography mobilities. Comparison of the synthetic analogs with the natural sulfolecithin showed them to be identical, except for the nature of the fatty acid chains, thus establishing the natural product as sn-3-phosphatidyl sulfocholine.