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. At temperatures below Tm (melting temperature), lipid bilayers enter a solid-like phase known as the gel phase. 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. M. A. Casadei was supported by a Research Studentship provided by the United Kingdom Biotechnology and Biological Sciences Research Council. Our results showing that resistance of E. coli NCTC 8164 decreases between 30 and 10°C are consistent with this previous finding. (45) examined the relationship between pressure inactivation of stationary-phase cells of L. plantarum and inactivation of the multidrug transporter HorA. Copyright © 2020 American Society for Microbiology | Privacy Policy | Website feedback, Print ISSN: 0099-2240; Online ISSN: 1098-5336, School of Food Biosciences, University of Reading, Whiteknights, Reading RG6 6AP, United Kingdom, Role of Membrane Fluidity in Pressure Resistance of, Sign In to Email Alerts with your Email Address. [ "article:topic", "license:ccby", "showtoc:no" ]. Similarly to the familiar transitions between the liquid, solid, and gas phases of simpler systems, these lipid phase transitions represent changes in the entropy of the system through reorganization of the system’s components in response to changes in the free energy of the system. Benalcazar, Wladimir A. Faller, R. BPH241 Lecture Notes. The positioning of double bonds in the fatty acid chain influences the degree to which Tm is lowered—with double bonds closer to the middle of the chain producing larger kinks, thereby decreasing Tm more than double bonds located closer to either end of the chain. Fatty acids with kinks often undergo trans isomerization, allowing the chains to be fully extended and strengthening Van der Waals interactions. Such gaps can allow cytoplasmic contents to leak out of the cell until they are plugged via lateral diffusion of neighboring lipids. The ratio of UFA to SFA has been used as an indirect indicator of membrane fluidity (11). These results support the hypothesis that fluidity has a greater effect in determining the resistance of exponential-phase cells than that of stationary-phase cells. Stronger Van der Waals interactions lead to tighter, more ordered lipid packing, impeding lateral movement across the surface of the membrane. The results suggest that the familial "biphasic linear" Arrhenius plots reported for many membrane enzymes and transport systems may, in fact, have more complex shapes, analysis of which can furnish useful information about the behavior of the enzyme molecule or transport system in its membrane environment. If pressure causes similar physical effects on bacterial membranes, then it is likely that membrane composition would affect the process and might therefore affect pressure resistance. 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). We verified the correspondence among growth temperature, the FI, and the physical behavior of the membrane by measuring the phase transition temperature of the phospholipid mixture extracted from whole cells by use of DSC. Enter multiple addresses on separate lines or separate them with commas. (b) Stationary-phase cells were grown at 37°C and pressure treated at 10°C (♦), 22°C (▴), or 29°C (□). J Bacteriol. Nevertheless, our DSC results clearly showed that the phase transition temperature of membrane phospholipids in E. coli NCTC 8164 increased linearly with temperature. National Center for Biotechnology Information, Unable to load your collection due to an error, Unable to load your delegates due to an error. A low melting temperature indicates the presence of fatty acids that promote fluidity while a high melting temperature indicates the presence of fatty acids and cholesterol that restrict fluidity. In stationary-phase cells, an unexpected and more complex picture emerged. Web. This technique measures the release or absorption of energy occurring when the physical state of the sample changes. 1988 Dec;170(12):5739-46. doi: 10.1128/jb.170.12.5739-5746.1988. 1992 Jun 11;1107(1):111-8. doi: 10.1016/0005-2736(92)90335-j. However, Tm can vary between lipids due to differing structural properties. Arrhenius plots of the ATPase activity in membranes containing only liquid-crystalline lipids are gently curved and have the same form regardless of the membrane fatty liver composition. Physics 563 Term Essay. Please enable it to take advantage of the complete set of features! We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Web. eCollection 2016. The liquid disordered phase, as its name implies, is a highly fluid state in which individual lipids can move laterally across the surface of the membrane relatively unhindered. Membrane fluidity and pressure resistance. Lipid unsaturation—the presence of one or more double bonds in the lipid’s fatty acid tails—also affects Tm by altering the strength of Van der Waals interactions between lipid tails. Get the latest research from NIH: https://www.nih.gov/coronavirus. Lipids can exist in a number of phases, which are summarized below. We propose that differences in resistance below the optimum temperature are caused mainly by differences in membrane fluidity, with lower treatment temperatures causing a stiffening of the membrane and consequent loss of pressure resistance (at higher treatment temperatures above the optimum, cellular inactivation may be a more complex process in which cell structures additional to the membrane are involved). This is consistent with the observations of Mejía et al. (44), who showed that exponential-phase cells of Lactobacillus plantarum grown at 10°C were more pressure resistant than those grown at 30°C. Membrane fluidity and pressure resistance.To assess the relationship among growth temperature, the FI, and the melting behavior of membrane lipids, total phospholipids were extracted from stationary-phase cells grown at different temperatures and analyzed by DSC. 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. 23 showed that polar carotenoids could reduce membrane fluidity above the transition temperature and had a fluidizing effect below it, a mechanism also known from cholesterol. Biophysical Journal. Effect of growth temperature on the membrane FI of exponential-phase (•) and stationary-phase (○) cells. 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). University of California, Davis. (4) used microscopy to examine the effect of pressure on vesicles composed of egg yolk phosphatidylcholine.

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