including non-bilayer preferring lipids [39]. Inverted micelle, a kind of non-bilayer
structure was also closely related to membrane fusion [40]. In addition to these
results, induction of non-bilayer preferring lipid, diacylglycerol into lipid membrane
promoted membrane fusion [41] and also generation of diacylglycerol by catalytic
conversion by phospholipase C induced membrane fusion [42]. Calcium ions induce
membrane fusion in lipid membrane including negatively charged acidic phospholipids and inverted micelles are involved in this case, and calcium ionophore for
calcium ion permeation [31] is supposed to be similar mechanism shown in Fig. 6.5.
6.5.3 Regulation of Biomembrane Formation by Non-bilayer
Structure as Lipid Storeroom in Biomembrane Lipid
Inner membrane of mitochondria and thylakoid membrane contain much of
cardiolipin and phosphatidylglycerol and ratio of proteins to lipids is higher because
of electron transfer system. These membranes keep lipid bilayer structure despite
higher content of non-bilayer preferring lipids. To keep bilayer membrane structures,
excess content of non-bilayer preferring lipids are supposed to be stored as cubic
phase or hexagonal II phase induced by calcium ions. These non-bilayer structures
function as buffer for lipid supplying store in case of protein degradation or protein
assembly [43]. Conversion between lipid bilayer membranes and non-bilayer membrane induced by changes of temperature and lipid composition was demonstrated in
a model system composed of mono-methyl phosphatidylethanolamine (DOPE-Me)
containing dipalmitoyl glycerol as non-bilayer preferring lipid by use of X-ray
diffraction, DSC and freeze-fractured electron microscope [44].
6.5.4 Changes of Structure and Physical Property
and Biological Function in Biomembranes
Three methyl moieties of phosphatidylcholine are replaced by hydrogen atoms in
phosphatidylethanolamine and result in structural change from cylinder to cone. And
change of physical property appears in change of phase transition temperature. Phase
transition temperature of dimyristoylphosphatidylethanolamine (DMPE) is
27 degrees higher than that of phosphatidylcholine (DMPC). Density of DMPC
membrane is 1.13 g/cm
3 compared to1.25 g/cm
3 of DMPE membrane in gel phase.
These physical properties of DMPE indicate narrower inter molecular distances
between DMPE molecules and stronger inter molecular interaction. Therefore,
non-bilayer membrane structure is supposed to raise lateral pressure from both
sides of membrane protein and to maintain functional structure of the membrane
proteins [43]. Indeed, protein translocase of E. coli was activated by non-bilayer
preferring lipids [45]. Formation of non-bilayer membrane structure is geometrical
90
6 Physical Properties of Biomembranes and Cellular Functions
structure was also closely related to membrane fusion [40]. In addition to these
results, induction of non-bilayer preferring lipid, diacylglycerol into lipid membrane
promoted membrane fusion [41] and also generation of diacylglycerol by catalytic
conversion by phospholipase C induced membrane fusion [42]. Calcium ions induce
membrane fusion in lipid membrane including negatively charged acidic phospholipids and inverted micelles are involved in this case, and calcium ionophore for
calcium ion permeation [31] is supposed to be similar mechanism shown in Fig. 6.5.
6.5.3 Regulation of Biomembrane Formation by Non-bilayer
Structure as Lipid Storeroom in Biomembrane Lipid
Inner membrane of mitochondria and thylakoid membrane contain much of
cardiolipin and phosphatidylglycerol and ratio of proteins to lipids is higher because
of electron transfer system. These membranes keep lipid bilayer structure despite
higher content of non-bilayer preferring lipids. To keep bilayer membrane structures,
excess content of non-bilayer preferring lipids are supposed to be stored as cubic
phase or hexagonal II phase induced by calcium ions. These non-bilayer structures
function as buffer for lipid supplying store in case of protein degradation or protein
assembly [43]. Conversion between lipid bilayer membranes and non-bilayer membrane induced by changes of temperature and lipid composition was demonstrated in
a model system composed of mono-methyl phosphatidylethanolamine (DOPE-Me)
containing dipalmitoyl glycerol as non-bilayer preferring lipid by use of X-ray
diffraction, DSC and freeze-fractured electron microscope [44].
6.5.4 Changes of Structure and Physical Property
and Biological Function in Biomembranes
Three methyl moieties of phosphatidylcholine are replaced by hydrogen atoms in
phosphatidylethanolamine and result in structural change from cylinder to cone. And
change of physical property appears in change of phase transition temperature. Phase
transition temperature of dimyristoylphosphatidylethanolamine (DMPE) is
27 degrees higher than that of phosphatidylcholine (DMPC). Density of DMPC
membrane is 1.13 g/cm
3 compared to1.25 g/cm
3 of DMPE membrane in gel phase.
These physical properties of DMPE indicate narrower inter molecular distances
between DMPE molecules and stronger inter molecular interaction. Therefore,
non-bilayer membrane structure is supposed to raise lateral pressure from both
sides of membrane protein and to maintain functional structure of the membrane
proteins [43]. Indeed, protein translocase of E. coli was activated by non-bilayer
preferring lipids [45]. Formation of non-bilayer membrane structure is geometrical
90
6 Physical Properties of Biomembranes and Cellular Functions