Homeoviscous adaptation

Sinensky, M. (1974) Homeoviscous adaptation - a homeostatic process thatregulates the viscosity of membrane lipids in Escherichia coli. Proceedings of the National Academy of Sciences of the, 71 (2), 522-525. 

Murray, S.M., O Brien, R.A., Mattson, K.M., Ceccarelli, C., Sykora, R.E. and West, K.N. Jr. (2010) Fluid-mosaic model, homeoviscous adaptation, and ionic liquids dramatic lowering of the melting point by side-chain unsaturation. Angewandte Chemie International Edition, 49 (15), 2755-2758. 

The earliest general model of adaptation to temperature in membrane lipids focused on the physical state ( static order or viscosity [= 1 / fluidity ]) of the bilayer. The finding that the physical state of membrane lipids from Escherichia coli cultured at different temperatures was similar at the different growth temperatures led to the homeoviscous adaptation hypothesis, which states that lipid composition is modified during thermal acclimation to facilitate retention of a relatively stable membrane physical state (Sinensky, 1974). At the outset of any discussion of homeoviscous adaptation, it is important to examine carefully what is meant by physical state (or the related terms static order, viscosity, and fluidity ). In such an analysis, one must also consider the physical methods that are used to make such measurements—and the limitations of these techniques. 

Figure 7.21. Homeoviscous adaptation of brain synaptosomal membranes. (A) Effects of measurement temperature on the physical states of synaptosomal membranes of differently adapted vertebrates, as determined by fluorescence anisotropy using l,6-diphenyl-l,3,5-hexatriene (DPH) as the probe. (B) DPH anisotropy at each species adaptation temperature. The horizontal lines enclose species where essentially complete homeoviscous adaptation was found. (Figure modified after Logue et al., 2000.)...

Homeophasic and Homeoviscous Adaptation Correlations with Biochemical, Physiological, and Behavioral Functions... 

Parenthetically, it should be noted that mitochondrial respiration rates normalized to mitochondrial protein content do not exhibit a significant degree of compensation to temperature (see Johnston et al., 1994). For mitochondria, then, changes in membrane physical state linked to homeophasic and homeoviscous adaptation do not appear linked to temperature-compensatory changes in specific activities of enzymes. 

Adaptation of the nervous system to temperature is likely to play a major role in governing the thermal tolerance ranges and thermal optima of animals (Cossins and Bowler, 1987). Conduction along axons and, particularly, transmission of signals at synapses are strongly affected by temperature. It is probable, therefore, that alterations in the properties of neural membranes will be found to correlate closely with changes in the thermal sensitivity of behavior. The nearly perfect homeoviscous adaptation of brain synaptosomes from differently... 

Cossins, A.R., K. Bowler, and C.L. Prosser (1981). Homeoviscous adaptation and its effects upon membrane-bound enzymes. J. Therm. Biol. 6 183-187. 

Hazel, J.R. (1988). Homeoviscous adaptation in animal cell membranes. In Advances in Membrane Fluidity. Physiological Regulation of Membrane Fluidity, pp. 149-188, ed. R.C. Aloia, C.C. Curtain, and L.M. Gordon. New York Liss. 

Hazel, J.R. (1995). Thermal adaptation in biological membranes—is homeoviscous adaptation the explanation Annu. Rev. Physiol. 57 19 42. 

Raynard, R.S. and A.R. Cossins (1991). Homeoviscous adaptation and thermal compensation of sodium pump of trout erythrocytes. Am. J. Physiol. 260 (Regulatory Integrative Comp. 

This example strikingly demonstrates the activity of living systems and their ability to maintain the optimal state of their membranes, and is a clear example of so-called homeoviscous adaptation. A definite advantage of homogeneous hydrogenation as compared with other methods is that isothermal conditions could be used. 

In the presence of diluent molecules in the extracellular medium, microorganisms tend to decrease the fluidity of their cytoplasmic membranes. The decreased fluidity of the cytoplasmic membrane increases its rigidity and viscosity, thus reducing the ability of the diluent molecules to penetrate into the structure of the cytoplasmic membrane [2]. Three mechanisms by which the fluidity of the cytoplasmic membrane can be decreased have been reported in the literature to date. The first one is the homeoviscous adaptation which involves changing the proportions of fatty acids in the membrane hpids [19, 22-25]. The second mechanism is the increase in the relative concentration of proteins relative to hpids in the cytoplasmic membrane [26]. The third mechanism involves the change in ceU shape and has been reported for archae [18]. 

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