An ordered metastable phase in hydrated phosphatidylethanolamine: The Y-transition

Institute of Biophysics, Bulgarian Academy of Sciences, Acad. G. Bonchev str. 21, 1113, Sofia, Bulgaria.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 03/1999; 1417(1):183-90. DOI: 10.1016/S0005-2736(98)00259-4
Source: PubMed


By using time-resolved X-ray diffraction, differential scanning calorimetry and scanning densitometry, we observed rapid formation at low temperature of a metastable ordered phase, termed LR1 phase, in fully hydrated dihexadecylphosphatidylethanolamine (DHPE). The LR1 phase has the same lamellar repeat period as the gel Lbeta phase but differs from the latter in its more ordered, orthorhombic hydrocarbon chain arrangement. It forms at about 12 degrees C upon cooling and manifests itself as splitting of the sharp, symmetric wide-angle X-ray peak of the DHPE gel phase into two reflections. This transition, designated the 'Y-transition', is readily reversible and proceeds with almost no hysteresis between cooling and heating scans. Calorimetrically, the LR1-->Lbeta transition is recorded as a low-enthalpy (0.2 kcal/mol) endothermic event. The formation of the LR1 phase from the gel phase is associated with a small, about 2 microl/g, decrease of the lipid partial specific volume recorded by scanning densitometry, in agreement with a volume calculation based on the X-ray data. The formation of the equilibrium Lc phase was found to take place from within the LR1 phase. This appears to be the only observable pathway for crystallisation of DHPE upon low-temperature incubation. Once formed, the Lc phase of this lipid converts directly into Lbeta phase at 50 degrees C, skipping the LR1 phase. Thus, the LR1 phase of DHPE can only be entered by cooling of the gel Lbeta phase. The data disclose certain similarities between the low-temperature polymorphism of DHPE and that of long-chain normal alkanes.

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Available from: Rumiana Koynova, Oct 03, 2015
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    • "Changing to basic medium, pH = 9 and mr = 50, only lamellar structures are seen, but, upon heating, the SAXS patterns split into two, giving an inverted Y shape to the sequence (Figure 4). The same phenomenon was observed by Tenchov et al. [20], in the WAXS region of the scattering patterns of fully hydrated DHPE, where they identified an ordered metastable phase in phosphatidylethanolamine (Ytransition ), whose splitting was observed at í µí±‡ < 12 upon cooling from the gel phase, with a lattice size of 6.08 nm. Prior to the splitting, their WAXS patterns showed a peak corresponding to 0.417 nm, characteristic for a hexagonal chain arrangement. "
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    03/2013; 2013(2):592318. DOI:10.1155/2013/592318
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    • "Specifically, while the first reflection seems equally intense in both lipids, the second and third reflections of the L c1 phase in the di-15:0 lipid are closer together and are also of similar intensity, whereas the second reflection is much stronger in intensity than the third reflection in the di-14:0 lipid (inset Fig. 6D). This suggests that differences in hydrocarbon chain end group contributions may be distorting the chain packing in the T || subcell of the odd-chained lipid (Tenchov et al., 1999). "
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