8.3 Temperature Acclimation of Cells and Physical
Properties of Membranes
As a cell is an essential unit of life and important biological functions are located on
biomembranes, influence of change in external temperature on biomembranes is
focused in particular on statistical physical properties of lipid bilayer membranes
such as phase transition and phase separation. In addition, membrane fluidity is an
expression of lateral diffusion and rotational diffusion of molecules composed in
lipid bilayer membranes. Physical properties of biomembranes depend on molecular
composition of the biomembranes. Lipid composition of biomembranes is modified
during temperature acclimation by enzymatic metabolism. Metabolic conversion of
lipid composition is also important in signal transduction mechanism of cell. Both
adaptation of cell to external environment and signal transduction of a cell include
development and division of a cell, which are essential parts of regulation of cellular
function. And these responses to external stimuli are supposed to be originated from
common origin.
8.4 Temperature Acclimation of Cells Observed by Phase
Transition and Membrane Fluidity
R.N. McElhaney and K.A. Souza found temperature acclimation of cell appeared on
phase transition in Bacillus subtilis by use of DSC. When Bacillus subtilis cells were
cultured at 42, 58 and 62
C, phase transition temperature of each culture of cells
were shown at temperature 10 degrees below temperature of the culture in wild type
cells. However, phase transition appeared around 30
C for mutant unable to live
above 60
C when the mutant cells were cultured at 42, 52 and 58
C [2]. Phenomenon that phase transition temperature shifted corresponding to culture temperature
was not observed in this mutant. And the result indicates that mechanism of
temperature acclimation is coded on gene. Bacillus subtilis is a prokaryote that
does not have any organelle such as nucleus, mitochondria endoplasmic reticulum
and Golgi apparatus. On the other hand, the authors observed similar temperature
acclimation in an eukaryote, Tetrahymena having organelle as intracellular membrane structures. Tetrahymena cells cultured at different temperatures were measured by DSC in the first heating scan and the second heating scan. At the first scan
large peak from protein denaturation appeared on DSC thermograph. Figure 8.1
shows the second scan and phase transition from lipid membranes of Tetrahymena
cells. Phase transition is accompanied with structural change, and transition of the
membrane structure depends on culture temperature of Tetrahymena cell, which is
observed by X-ray diffraction [3, 4]. Lipids of biomembranes are composed of
various species of lipid molecules. Phase transition temperature of each lipid is
8.4 Temperature Acclimation of Cells Observed by Phase Transition and. . .
161
Properties of Membranes
As a cell is an essential unit of life and important biological functions are located on
biomembranes, influence of change in external temperature on biomembranes is
focused in particular on statistical physical properties of lipid bilayer membranes
such as phase transition and phase separation. In addition, membrane fluidity is an
expression of lateral diffusion and rotational diffusion of molecules composed in
lipid bilayer membranes. Physical properties of biomembranes depend on molecular
composition of the biomembranes. Lipid composition of biomembranes is modified
during temperature acclimation by enzymatic metabolism. Metabolic conversion of
lipid composition is also important in signal transduction mechanism of cell. Both
adaptation of cell to external environment and signal transduction of a cell include
development and division of a cell, which are essential parts of regulation of cellular
function. And these responses to external stimuli are supposed to be originated from
common origin.
8.4 Temperature Acclimation of Cells Observed by Phase
Transition and Membrane Fluidity
R.N. McElhaney and K.A. Souza found temperature acclimation of cell appeared on
phase transition in Bacillus subtilis by use of DSC. When Bacillus subtilis cells were
cultured at 42, 58 and 62
C, phase transition temperature of each culture of cells
were shown at temperature 10 degrees below temperature of the culture in wild type
cells. However, phase transition appeared around 30
C for mutant unable to live
above 60
C when the mutant cells were cultured at 42, 52 and 58
C [2]. Phenomenon that phase transition temperature shifted corresponding to culture temperature
was not observed in this mutant. And the result indicates that mechanism of
temperature acclimation is coded on gene. Bacillus subtilis is a prokaryote that
does not have any organelle such as nucleus, mitochondria endoplasmic reticulum
and Golgi apparatus. On the other hand, the authors observed similar temperature
acclimation in an eukaryote, Tetrahymena having organelle as intracellular membrane structures. Tetrahymena cells cultured at different temperatures were measured by DSC in the first heating scan and the second heating scan. At the first scan
large peak from protein denaturation appeared on DSC thermograph. Figure 8.1
shows the second scan and phase transition from lipid membranes of Tetrahymena
cells. Phase transition is accompanied with structural change, and transition of the
membrane structure depends on culture temperature of Tetrahymena cell, which is
observed by X-ray diffraction [3, 4]. Lipids of biomembranes are composed of
various species of lipid molecules. Phase transition temperature of each lipid is
8.4 Temperature Acclimation of Cells Observed by Phase Transition and. . .
161