Fatty acids inositol lipids

Global lipid profiling methods typically cover molecular lipid species from the major classes of lipids such as cholesteryl esters, ceramides, mono-(MG), di- (DG), and TGs, and membrane PLs, for example, sphingomyelins (SMs), PCs, phosphatidylethanolamines (PEs), PSs, and lysophospholipids. In targeted lipid analysis, specific lipid classes that are poorly covered by the global profiling methods are usually analyzed. These lipids include steroids, sterols, bile acids, fatty acids, signaling lipids such as eicosanoids, and ceramides, as well as polar lipids and inositol lipids. 

There exists an unusual uniformity in the fatty acid composition of the inositol lipids. All three of the major phosphoinositides are enriched in the 1-stearoyl, 2-arachidonoyl ( ST/AR ) sn-glycerol species (=80% in brain). The polyphosphoinositides (PI4P and PI(4,5)P2) are present in much lower amounts than PI. PI(4,5)P2 has been shown to be predominantly, although not... 

These are the most common class of complex lipid (Figure 12.11) and contain a phosphoric acid residue (phosphate group) and two fatty acids esterified to glycerol. Attached to the phosphate group is an amino alcohol, sometimes referred to as the nitrogenous base, which may be either serine, choline or ethanolamine or sometimes the monomethyl or dimethyl derivatives of ethanolamine (Table 12.4). Alternatively, a polyhydroxy compound which is either glycerol, myo-inositol or one of their derivatives is attached instead... 

DAG species are derived from three main routes (1) PLC-mediated hydrolysis of phospholipids (2) phosphatase-mediated hydrolysis of phosphatidic acid (PA) and (3) lipase-mediated hydrolysis of triacylglycerol (TAG) species (Fig. 2). Targeted lipidomic analyses show that the fatty acid compositions of the DAGs formed by these various routes reflect the composition of the parent lipid (Fig. 5). In particular, those derived from inositol phospholipids are highly enriched in... 

Arachidonic acid, a 20-carbon fatty acid, is the primary precursor of the prostaglandins and related compounds (see Figure 39.3). Arachidonic acid is present as a component of the phospholipids of cell membranes, primarily phosphatidyl inositol and other complex lipids.1 Free arachidonic acid is released from tissue phospholipids by the action of phospholipase A2 and other acyl hydrolases, via a process controlled by hormones and other stimuli (see Figure 39.3). There are two major pathways in the synthesis of the eicosanoids from arachidonic acid (see Figure 39.3). 

Gj, G0, Gq). As a result, the inner leaflet of the plasma membrane is the source of a variety of chemical mediators that are released as a consequence of receptor activation. These mediators include inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol (DAG), which are both products of Pi-specific phospholipase C (Fig. 6-23) and arachidonic acid, which is an unsaturated fatty acid product of phospholipase A2 and phosphatidate (a product of phospholipase D). IP3 induces the release of Ca2+ ions from intracellular endoplasmic reticulum stores. DAG is a known activator of a lipid-dependent serine/threonine protein kinase (protein kinase C). 

Acid hydrolyses are usually carried out by refluxing in 6 N aqueous hydrochloric acid (constant boiling) or 5 to 10% solutions of HC1 in methanol (to promote solubility) for 4 to 30 hr, depending on the lipid in question. Most glycerophosphatides are hydrolyzed by acid to fatty acids, glycerophosphate, and the free base, just as with alkali. However, inositol phosphatides initially yield inositol phosphate and diglycerides on acid hydrolysis. Hydrochloric acid is easily removed by vacuum, which makes chromatographic examination of the hydrolysis products easier. 

Tlie polar head group of the molecule regulates the overall charge and hydrophilicity of the membrane. The major polar groups in biomembranes may be choline, ethanolamine, serine, inositol, galactose or in some cases n-acetylneuraminic acid. The non-polar acyl-chains influence greatly the fluidity and the packing of the membrane. Saturated fatty acid residues while decrease the fluidity and produce more compact membranes, unsatiirated acyi-chains increase the fluidity and minimize the lipid orientation of the membrane. 

Although there are direct similarities between MSPD and SPE, the MSPD differs in that it appears to be a mixture of interactions, including partitioning, adsorption, and ion pairing, which makes this an effective method of sorption and extraction. It is possible to elute fractions that contain neutral lipids (hexane), phospholipids (dichloromethane), fatty acids and sterols (acetonitrile), a mixture of phospholipids, amino acids, inositols, mono-, disaccharides, and citric acid (methanol), and finally nucleotides and protein (water). 

Complex interactions and displacements of the omega-3 and omega-6 fatty acids take place in plasma and cellular lipids after dietary manipulations. Early steps of cell activation, such as generation of inositol phosphates, are induced by dietary fatty acids (Galli et al., 1989). The effects of dietary fatty acids on the inositol phosphate pathway indicate that diet-induced modifications of PUFA at the cellular level affect the activity of the enzymes responsible for the generation of lipid mediators in addition to the formation of products (eicosanoids) directly derived from their fatty acid precursors. This shows that dietary fats affect key processes in cell function. 

Galli C, Mosconi C, Medini L. Colli S, Tremoli E. N-6 and N-3 fatty acids in plasma and platelet lipids, and generation of inositol phosphates by stimulated platelets after dietary manipulations in the rabbit. In Galli C, Simopoulos AP, eds. Dietary co3 and cob Fatty Acids Biological Effects and Nutritional Essentiality. Life Sciences Series Vol. 171. Plenu, New York, 1989, pp. 213-218. 

Fig. 1. Complex lipid forms and fatty acids in mammalian cells, including triglycerides, phosphatides with either choline, ethanolamine, serine or inositol, and shphigomyeUn. Fatty acid building blocks include oleic acid (CIS 1) and DHA (C22 6) in molecular structure form.

Precursors of membrane components, carbohydrates, amino acids, and other biogenic compounds formed either directly or indirectly from those chiral and non-chiral molecules delivered to Earth. Benzene, for instance, is one of the aromatic compounds of interstellar dust from which a precursor of the membrane lipid inositol-1-phosphate apparently derived by oxidation in a long series of chemical reactions. The structure of the important lipid, a derivative of inositol-phosphate in Fig. 6.1, displays two different fatty acid side chains (marked in blue and green) that frequently occur in membranes. 

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