Differential scanning calorimetry bilayer membranes

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... 

Hydration of phospholipid head groups is essential properties not only for stabilizing bilayer structures in an aqueous environment, but also for fusion or endocytosis of biological membranes including protein transfers [33-35]. Hydration or swelling behavior has only been studied by indirect methods such as X-ray diffraction [36], differential scanning calorimetry (DSC) [37], and H-NMR [38,39]. 

The influence of plant sterols on the phase properties of phospholipid bilayers has been studied by differential scanning calorimetry and X-ray diffraction [206]. It is interesting that the phase transition of dipalmitoylglycerophosphocholine was eliminated by plant sterols at a concentration of about 33 mole%, as found for cholesterol in animal cell membranes. However, less effective modulation of lipid bilayer permeability by plant sterols as compared with cholesterol has been reported. The molecular evolution of biomembranes has received some consideration [207-209]. In his speculation on the evolution of sterols, Bloch [207] has suggested that in the prebiotic atmosphere chemical evolution of the sterol pathway if it did indeed occur, must have stopped at the stage of squalene because of lack of molecular oxygen, an obligatory electron acceptor in the biosynthetic pathway of sterols . Thus, cholesterol is absent from anaerobic bacteria (procaryotes). 

The interesting property of the MPC copolymer is its affinity for phospholipids (5,72-74). The amount of a phospholipid, dipalmitoylphosphatidylcholine (DPPC), adsorbed on MPC copolymers was larger than that on polystyrene, poly(BMA) and poly(HEMA) and increased with increasing MPC moiety when the MPC copolymers were contacted with a liposomal solution of DPPC (5). This tendency was the same as that of the adsorption of phospholipid from human plasma which is indicated in Fig. 3. Thus, the affinity of poly(MPC-co-BMA) for the phospholipids could be observed even in the plasma. The DPPC molecules adsorbed on the poly(MPC-co-BMA) surface assumed an organized structure like that for a bilayer membrane, which was confirmed by differential scanning calorimetry(DSC) and X-ray photoelectron spectroscopy(XPS) when the poly(MPC-c -BMA) membrane was immersed in the solution containing DPPC (72,74) It is therefore concluded that the MPC copolymers stabilized the adsorption layer of phospholipids on the surface. Stabilization of the liposomal structure in water by a water-soluble MPC copolymer was also found (75). 

The hydrocarbon chains of the lipid bilayer are in a liquid-like state as evidenced by X-ray diffraction, electron spin resonance spectroscopy, and differential scanning calorimetry studies. A quantitative characterization of the hydrocarbon chain order in lipid bilayers by means of H-NMR became possible by selectively deuterating both fatty acyl chains in a lipid molecule. Measurement of the deuterium quadrupole splittings, Avq, allowed calculation of the order parameter of the C—D bond vector at each labeled carbon atom. The variation of the order parameter ScdI with the position of the labeled carbon atom in the membrane is the so-called order profile. An... 

Yet, physicochemical studies using differential scanning calorimetry, infrared spectroscopy and small-angle X-ray diffraction have shown that B[a]P incorporates into phospholipid bilayers and localizes in the most apolar region of the phospholipid matrix. This phenomenon may account for the observation of an expanded and swollen membrane [11]. We have therefore, proposed that distortion of the physiochemical properties of the adipocyte plasma membrane by B[a]P decreases the signalling capacity of G-coupled receptors intimately linked to the phospholipid bilayer, via their seven transmembrane domains. 

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