Freezing of phosphocholine headgroup in fully hydrated sphingomyelin bilayers and its effect on the dynamics of nonfreezable water at subzero temperatures

Journal Article · Thu Jul 25 00:00:00 EDT 1991 · Journal of Biological Chemistry; (United States)

OSTI ID:5394079

Wu, W G; Chi, L M; Yang, T S; Fang, S Y ^[1]

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1. Institute of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan, (China)

Differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spectroscopy are applied to characterize the nonfreezable water molecules in fully hydrated D2O/sphingomyelin at temperatures below 0 degrees C. Upon cooling, DSC thermogram displays two thermal transitions peaked at -11 and -34 degrees C. The high-temperature exothermic transition corresponds to the freezing of the bulk D2O, and the low-temperature transition, which has not previously been reported, can be ascribed to the freezing of the phosphocholine headgroup in the lipid bilayer. The dynamics of nonfreezable water are also studied by 2H NMR T1 (spin-lattice relaxation time) and T2e (spin-spin relaxation time obtained by two pulse echo) measurements at 30.7 MHz and at temperatures down to -110 degrees C. The temperature dependence of the T1 relaxation time is characterized by a distinct minimum value of 2.1 {plus minus} 0.1 ms at -30C. T2e is discontinuous at temperature around -70C, indicating another freezing-like event for the bound water at this temperature. Analysis of the relaxation data suggest that nonfreezable water undergoes both fast and slow motions at characteristic NMR time scales. The slow motions are affected when the lipid headgroup freezes.

• OSTI ID: 5394079
• Journal Information: Journal of Biological Chemistry; (United States), Vol. 266:21; ISSN 0021-9258
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
SPHINGOMYELINS
STRUCTURE-ACTIVITY RELATIONSHIPS
CHEMICAL COMPOSITION
DEUTERIUM
FREEZING
NUCLEAR MAGNETIC RESONANCE
SPIN ECHO
TEMPERATURE DEPENDENCE
THERMODYNAMICS
TRACER TECHNIQUES
WATER
ESTERS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
LIPIDS
MAGNETIC RESONANCE
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
OXYGEN COMPOUNDS
PHOSPHOLIPIDS
RESONANCE
STABLE ISOTOPES
550201* - Biochemistry- Tracer Techniques