Ni, number of cells after pressure treatment; N0, initial number of cells. The main peak temperature was linearly related to the growth temperature and to the FI, confirming the homeoviscous response of the cells to different growth temperatures and also the validity of this index as an indication of membrane fluidity.  |  The absolute ATPase activity at temperatures well above the lipid phase transition temperature varies in a complex fashion with fatty acid composition. NOTE: We request your email address only to inform the recipient that it was you who recommended this article, and that it is not junk mail. It is also possible that despite sonication in buffer, the phospholipids in our preparations were not fully hydrated, which would also have increased their melting temperature. However, other changes not necessarily related to envelope composition may also affect pressure resistance, so further work is needed to clarify this. Growth temperature and membrane fatty acid composition. (35) showed that pressures of 350 MPa and above cause substantial loss of protein from both cytoplasmic and outer membranes. The accumulation of sterols in a lipid bilayer causes tighter packing of fatty acid tails in liquid phase lipids and separates gel phase lipids. In E. coli, these changes result from the expression of over 50 genes, most of which are regulated by the alternative sigma factor RpoS (σs), but other regulatory elements such as the universal stress protein UspA are also involved (17). It is well known that stationary-phase cells are more pressure resistant than exponential-phase cells (5, 25). Unlike chain length, however, increasing unsaturation reduces the Tm of the lipid by reducing the accessible surface area of the fatty acid tail by forming kinks that prevent nearby tails from packing together as tightly. The melting point of UFA is lower than that of SFA, and the general effect of the incorporation of more UFA in the membrane is a decrease in the phase transition temperature (2). The liquid ordered phase represents something of a hybrid of the liquid disordered and gel phases. This leads to increasing Tm’s with increasing chain length, as shown in, Phase separation between lipids surrounding integral membrane proteins can briefly expose the hydrophobic residues of the middle of the protein to water. Characterization of sodium transport in Acholeplasma laidlawii B cells and in lipid vesicles containing purified A. laidlawii (Na+-Mg2+)-ATPase by using nuclear magnetic resonance spectroscopy and 22Na tracer techniques. As heat is increased, the membrane makes a sharp transition from a rigid state to a more fluid state. Fatty acid composition of exponential-phase cells of E. coli NCTC 8164 grown at different temperatures, Fatty acid composition of stationary-phase cells of E. coli NCTC 8164 grown at different temperatures. Pressure may be envisioned to have an irreversible effect on membrane proteins in one of two ways: either the proteins could be denatured in situ or they might be squeezed out of the membrane as a result of closer packing of membrane phospholipids. It would be of obvious interest to examine whether displacement of proteins was affected by the initial fluidity of the membrane. Membrane fluidity and pressure resistance.The effect of membrane fluidity on pressure resistance has been examined previously by using a fatty acid auxotroph of E. coli in which membrane composition can be altered independently of temperature (8). Tg + 3.60 (R2 = 0.97) (for stationary-phase cells), where Tg is the growth temperature. Quantitative analysis of the results suggests that ATPase is reversibly inactivated when its vicinal lipids undergo a transition to a state of reduced plasticity at low temperatures. Clipboard, Search History, and several other advanced features are temporarily unavailable. If such a membrane system is cooled, the longer, more saturated lipids will undergo the transition to the gel phase before other shorter, less saturated lipids, as their Tm will be reached first. Relationships between growth temperature and phase transition temperature (Tm) (a) and between Tm and FI (b) of phospholipids extracted from whole stationary-phase cells (error bars indicate standard deviation). Effect of growth temperature on the membrane FI of exponential-phase (•) and stationary-phase (○) cells. Growth temperature and membrane fatty acid composition.As expected, growth of E. coli NCTC 8164 at different temperatures resulted in differences in membrane fatty acid composition. Stationary-phase adaptation and pressure resistance.Despite the contribution of membrane fluidity to pressure resistance, it appears that more-fundamental changes affecting resistance occur during entry to stationary phase.

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