Role of lipid composition

Although the role of lipid composition in membrane function is not entirely understood, changes in composition can produce dramatic effects. Researchers have isolated fruit flies with mutations in the gene that encodes ethanolamine kinase (analogous to choline kinase Fig. 21-28). Lack of this enzyme eliminates one pathway for phosphatidylethanolamine synthesis, thereby reducing the amount of this lipid in cellular membranes. Flies with this mutation—those with the genotype easily shocked—exhibit transient paralysis following electrical stimulation or mechanical shock that would not affect wild-type flies. 

Bouwstra, J.A., et al. 1999. The role of ceramide composition in the lipid organisation of the skin barrier. Biochim Biophys Acta 1419 127. 

The surface-active properties of phospholipids (PL) are widely used for the formation of liposomes, which are a model of biomembranes and also a technique for the study of cells and exposure to them [1,2], Earlier it has been established the substantial role of lipids which contain in biosorbents for the regulation of properties of lipids in medium [3], It was also foimd that scale and character of interrelations between the different fractions in lipids of the mice tissue had a dependence on physicochemical properties of lipids [4, 5], and the physicochemical properties and composition of natural lipids have an influence on those of liposomes formed from them [6]. Besides, earlier it was shown the existence of physicochemical regulatory system of the lipid peroxidation (LPO) both a membrane and organ levels [7, 8]. It allows us to suggest the existence of a uniform mechanism of the regulatory in the LPO system both on the membrane and the organ levels. 

The results of our work present a new situation on the effect of lipid composition of the membrane on the role played by the membrane and on the regulation of the membrane-associated enzymes. The lipid composition of the membrane depends on the lipid composition of the diet which is primarily responsible for the regulatory characteristics affecting its associated-enz3nnes, independently of their locations and lipid dependency. 

Analysis of lipid-packing defects in curved bilayers as a function of lipid composition revealed the crucial role of lipid chemistry in the adaptation of lipid bilayers to membrane curvature and, in turn, of ALPS binding to curved membranes. 

Peroxidation of lipids is another factor which must be considered in the safety evaluation of liposome administration. Smith and coworkers (1983) demonstrated that lipid peroxides can play an important role in liver toxicity. Allen et al. (1984) showed that liposomes protected by an antioxidant caused less MPS impairment than liposomes subjected to mild oxidizing conditions. From the study of Kunimoto et al. (1981) it can be concluded that the level of peroxidation in freshly prepared liposome preparations and those on storage strongly depends both on the phospholipid fatty acid composition and on the head group of the phospholipid. Addition of appropriate antioxidants to liposomes composed of lipids which are liable to peroxidation and designed for use in human studies is therefore necessary. 

Most hydrophilic, or water-soluble, substances are repelled by this hydrophobic interior and cannot simply diffuse through the membrane. Instead, these substances must cross the membrane using specialized transport mechanisms. Examples of lipid-insoluble substances that require such mechanisms include nutrient molecules, such as glucose and amino acids, and all species of ions (Na+, Ca++, H+, Cl, and HC03). Therefore, the plasma membrane plays a very important role in determining the composition of the intracellular fluid by selectively permitting substances to move in and out of the cell. 

Unsaturations of lipids play a key role in lipid homeostasis, where organisms adapt to temperature variations of the environment. Plants and animals maintain physiological functions by reversibly altering the composition and conformation of lipid molecules of the cell membrane. To achieve this, they extensively and elegantly use the unsaturations (double bonds) present in their side chains. This is the process by which cell membranes adjust their flexibility (fluidity) of the bilayer and adapt themselves to perturbations in temperature, pressure, and other variations in the natural environment [11-14]. They remain indispensable for the poikilothermism exhibited by fishes, invertebrates, and amphibians [15, 16]. Commercially,... 

The lipid compositions of plasma membranes, endoplasmic reticulum and Golgi membranes are distinct 26 Cholesterol transport and regulation in the central nervous system is distinct from that of peripheral tissues 26 In adult brain most cholesterol synthesis occurs in astrocytes 26 The astrocytic cholesterol supply to neurons is important for neuronal development and remodeling 27 The structure and roles of membrane microdomains (rafts) in cell membranes are under intensive study but many aspects are still unresolved 28... 

Lipids have critical roles in nervous system structure and function. Synaptic complexes and myelin are characterized by unique lipid compositions that contribute to the specialized properties of these nervous system structures. Multiple signaling pathways involving lipid intermediates regulate cell differentiation and synaptic transmission. 

Eukaryotic cells have evolved a complex, intracellular membrane organization. This organization is partially achieved by compartmentalization of cellular processes within specialized membrane-bounded organelles. Each organelle has a unique protein and lipid composition. This internal membrane system allows cells to perform two essential functions to sort and deliver fully processed membrane proteins, lipids and carbohydrates to specific intracellular compartments, the plasma membrane and the cell exterior, and to uptake macromolecules from the cell exterior (reviewed in [1,2]). Both processes are highly developed in cells of the nervous system, playing critical roles in the function and even survival of neurons and glia. 

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