Temperature shift, fatty acid composition

Comparson of the transitions observed by differential scanning calorimetry in membranes of M. laidlawii and in water dispersions of the lipids from the membranes support the concept that most of the lipids exist as a smectic mesophase in the membranes. The evidence for a bilayer structure is straightforward in this case. Lipid transition temperatures are a function of fatty acid composition and correlate well with biological properties. The calorimeter possesses advantages over high resolution NMR for M. laidlawii, and perhaps in many other systems, because the data can be interpreted less ambiguously. In M. laidlawii membranes the bilayer appears to be compatible with the same physical properties observed in other membranes—a red-shifted ORD, lack of ft structure in the infrared, reversible dissociation by detergents, and poorly... 

In this study, we investigated the temperature-induced changes in glycerolipid and fatty acid composition under isothermal conditions and the desaturation of fatty acids after a downward temperature shift in the cyanobacterium, Syneohooystis PCC 6803. 

When the effect of temperature shift on the fatty acid composition was studied, cells grown at 5 C were washed with 0.5 M NaCl and suspended in a non-growing medium (5 mM Tris, 0.4 M NaCl, 10 mM KCl, 5 mM MgCl2r and 1 M glycerol, pH 7.5) at 5 C at a concentration of 1.5X10 cells/ml. After cerulenin was added at 10 jag/ml to inhibit de novo synthesis of fatty acids, the temperature of the cell suspension was shifted from 5°C to 20°C. A portion of the cell suspension was withdrawn at appropriate intervals and subjected to lipid extraction. 

Table 2. Changes in fatty acid composition of the total lipids in Vibrio ABL -I after temperature-shift up from 5 C to 20 C in the presence of cerulenin (10 jug/ml)...

When the growth temperature is suddenly increased or decreased, the fatty acid composition of A. variabilis is rapidly altered (Sato and Murata, 1980a, b). For 10 h after the temperature shift from 38 to 28°C, the total amount of lipids stays at a constant level (Sato and Murata, 1980a), but a decrease in 16 0 and a concomitant increase in 16 1 take place at the C-2 position of MGDG. Then, as fatty acid and lipid synthesis resumes, the ratio of 16 0 to 16 1 is slowly restored to that seen prior to the temperature shift. This type of transient desaturation of 16 0 to 16 1 is not observed in the other major lipid classes such as DGDG. 

Irrespective of different features of the phase transition of the plasma and thylakoid membranes, there is no discernible difference between the plasma membranes and thylakoid membranes with respect to their polar lipid and fatty acid composition (Omata and Murata, 1983). The higher phase transition temperature of the thylakoid membrane with respect to the plasma membrane may be due to the high protein content of the thylakoid membranes, 7QfH> of the dry weight, compared with the corresponding value of 40% found in the plasma membranes (Omata and Murata, 1983). The shift in phase transition temperature due to the growth temperature corresponds to the growth temperature-dependent alteration in the fatty acid composition (Holton et al., 1964 Sato et al., 1979). 

Cells regulate the lipid compositions of their plasma membrane so that a reasonable membrane fluidity is main-tained. They do this by controlling fatty acid biosynthesis so as to vary the lengths of the fatty acid chains and the ratio of unsaturated to saturated fatty acids (see chapter 19). If cells are grown at low temperatures, their phospholipids contain more unsaturated fatty acids or fatty acids with shorter chains or both. These adjustments shift the Tm to lower temperatures, with the result that (to the extent that the melting transition is sharp enough to be measureable) the Tm re-... 

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