Phosphatidylethanolamine , phase behavior

McMullen, T., Lewis, R., and McElhaney, R. Calorimetric and spectroscopic studies of the effects of cholesterol on the thermotropic phase behavior and organization of a homologous series of linear saturated phosphatidylethanolamine bilayers, Biochim. Biophys. Acta, 1416,119,1999. 

Epand RM, Fuller N, Rand RP. Role of the position of unsaturation on the phase behavior and intrinsic curvature of phosphatidylethanolamines. Biophys J 1996 71 1806-1810. 

The influence of the amount of cholesterol at various temperatures on the thermotropic phase behavior and organization of saturated phosphatidylethanolamine bilayers has been... 

Although phosphatidylserine is in general asymmetrically distributed in cell membranes with the bulk of this lipid in the cytoplasmic leaflet of the bilayer, some phosphatidylserine appears to reside in the outer lipid monolayer of the axonal membrane. Furthermore, this phosphatidylserine is involved in the nerve action potential. Treatment of an axon with extracellular serine decarboxylase converts phosphatidylserine to -ethanolamine, which results in a decrease in the action potential spike height. Catalysis of the reversed reaction by this enzyme in the presence of excess L-serine converts phosphatidylethanolamine to -serine. This produces an average of 28% increase in the action potential amplitude. It is worth noticing that several anaesthetic compounds have been shown to bind phosphatidylserine in vitroThe role of phosphatidylserine phase behavior in the nerve action potential will be discussed in somewhat more detail in Section 7. 

Fig. 2 The phase behavior of mixed-chain phosphatidylethanolamine in excess water. At low temperature this lipid exists as crystalline bilayers (the gel or Lq state). With increasing temperature the bilayers undergo a reversible endothermic transition commonly called the bilayer phase transition. The resulting state (the liquid crystalline or L3 state) is composed of fluid bilayers. The lipid hydrocarbon chains are more disordered in fluid bilayers than in crystalline bilayers. This results in more cone-shaped molecules as illustrated in the top of the figure. With further increase in temperature the lipid molecules become still more cone-shaped and their preferred conformation is the inverted hexagonal En state.

The structurally somewhat more complicated lipids may show in the pure state quite similar sequences of phase transitions as the soaps. Their behavior may be illustrated by the transitions of 1,2-dimyristoyl-DL-phosphatidylethanolamine [CH3-(CH2-),2C0-0-]CH2[CH3(CH2-)oC0-0-]CH-CH2-[0-P0r - 0-(CH3-)2-NH >]. 

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