Photon Factory Activity Report 2004 #22 Part B (2005)
Biological Science

9C, 15A/2003G138

Structure and phase behavior of synthetic sphingomyelin analogue:
1,2-dimyristamido-1,2-deoxyphosphatidylcholine
Hiroshi TAKAHASHI*1, Yukihisa OKUMURA2, Junzo SUNAMOTO3
1
Gunma Univ., Maebashi, Gunma 371-8510, Japan
2
Shinshu University, Nagano, 380-8553, Japan, 3Prof. Emeritus, Kyoto Uni., Japan
Introduction
Acylamino-phospholipid,
1,2-dimyristamido-1,2deoxyphosphatidylcholine (DDPC) has two amide bonds,
instead of two ester bonds in dimyristoylphosphatidylcholine. The DDPC was synthesized as an analogue ofsphingomyelin [1]. Recently, sphingomyelin, one of themost abundant sphingolipids in biological membrane, hasbeen recognized as an important molecule for theformation of functional lipid domains, so-called "lipidrafts". The lipid raft domains are thought to play
important roles in many biological processes. Masseriniand Ravasi [2] have proposed a hypothesis that anintermolecular hydrogen bond between hydroxyl andamide groups of the ceramide moiety of sphingolipids is
one of the main driving forces of lipid raft formation.
The aim of this study is to get basic knowledge on thephysical properties that is needed to discuss the functionof the lipids having amide bonds in the raft formation. To
this end, we investigated the structure and phase behaviorof hydrated DDPC bilayers by means of differential
scanning calorimetry (DSC) and X-ray diffraction.
Materials and Methods
DDPC was synthesized from a starting material,
diaminopropanol. The detailed methods of the synthesis
and purification have been reported elsewhere [1].
Simultaneous X-ray diffraction and differential scanningcalorimetry (DSC) measurements with synchrotron
radiation were performed at the station BL9C of Photon
Factory at KEK, Tsukuba, Japan. Normal small angle Xray diffraction measurements were also performed at thestation BL15A.
Results and Discussion
Figure 1 shows a typical data obtained bysimultaneous X-ray diffraction and DSC measurements.
From these data, we found that hydrated DDPC bilayer
samples exhibits a metastable phase behavior. By coolingofrom a chain-melted state at the rates of greater than 4 C-1
min , hydrated DDPC bilayers form a metastable gelphase. In the gel phase, the hydrophobic chains are tilted
with respect to the bilayer normal. By heating, themetastable gel phase is transformed in to a stable phaseoassociated with an exothermic heat event at 18.3 C andthen the stable phase is transformed into a liquidoocrystalline phase at 25.6 C. The incubation at 17 C for
more than 1 hour also induces the formation of the stable

Fig.1 Comparison among small- and wide-angle Xray diffraction and DSC data obtained simultaneouslyfor hydrated DDPC samples. The scanning rate waso-1
2.0 C min . (A) Heating scan after cooling from 40
ooC to 0 oC. (B) Heating scan after cooling from 17 Cooto 0 C following more than 1hr incubation at 17 C.
For the DSC data, the horizontal and vertical axes
represent heat flow and temperature, respectively.

phase. The further detail results and discussion aredescribed elsewhere [3].
References[1] J. Sunamoto et al., Biochim. Biophs. Acta 1024, 209219 (1990).
[2] M. Masserini, D. Ravasi, Biochim. Biophs. Acta 1532,149-161 (2001).
[3] H. Takahashi et al., Biochim. Biophs. Acta (in press)(2005).
*htakahas@fs.aramaki.gunma-u.ac.jp

222

Users' Report