Pulse NMR study of the interaction of calcium ion with dipalmitoylphosphatidylcholine lamellae.
Molecular motion of dipalmitoylphosphatidylcholine (DPPC)/CaCl2 lamellae in a gel phase was studied by pulse NMR. Proton 1/T1 for DPPC in a gel phase showed that the rate of reorientation about the long axis of the lipid molecule decreased gradually from 0 to 500 mM CaCl2. At 10-50 mM CaCl2 the correlation time reached the value of the inverse Larmor frequency (approx. 2.6 ns). A proton NMR absorption spectrum and a spin-pair-dipolar-echo (SPDE) decay showed that the second moment in the hydrocarbon chain region decreased below about 1 mM CaCl2 and increased from 1 to 500 mM CaCl2. The second moment in the polar head group increased gradually with an increase in the CaCl2 concentration. The increase in the second moment at the high CaCl2 concentrations was attributed to an increase in the order parameters of the segments both in the polar head group and in the hydrocarbon chain region. At the lower CaCl2 concentrations, however, calcium ion possibly induced disorder in the lamellae which led to a decrease in the order parameter in the hydrocarbon chain region.
Shibata
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Riken Institute of Physical and Chemical Research, Saitama, Japan.
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005782:Gels; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D013057:Spectrum Analysis
D005782:Gels; D008051:Lipid Bilayers; D015060:1,2-Dipalmitoylphosphatidylcholine; D002118:Calcium