Acyl chain composition

Phase transitions have been characterized in a number of different pure and mixed lipid systems. Table 9.1 shows a comparison of the transition temperatures observed for several different phosphatidylcholines with different fatty acyl chain compositions. General characteristics of bilayer phase transitions include the following ... 

A heterogeneous mixture of fatty amide chains often is found in natural sphingomyelins and other sphingolipids, varying with the source and age (30). The fatty acyl chain content of milk sphingomyelin, for example, is 33% C23 0, and -20% each of C16 0, C22 0, and C24 0. About 50% of the A-acyl chain composition of bovine brain sphingomyelin... 

The fact that this biosynthetic pathway is common to other NAEs, and that the percentage fatty acyl chain composition of these compounds in tissues is ultimately dependent on that of the sn-l position of phospholipids (Fig. 2), explains why AEA is the minor of its congeners. 

Modulation of Receptor Signaling by Phospholipid Acyl Chain Composition... 

The importance of investigating how cholesterol content and acyl chain composition alter the physical properties of membranes is highlighted by the functional deficits associated with 22 6n-3-deficient diets and the antisocial behavior associated with varied cholesterol levels. In the context of psychological disease and neurotransmitter receptor function, it is important to investigate how compositionally induced changes in membrane physical properties influence membrane-associated signaling processes. 

Examples of the effects of acyl chain composition and cholesterol on the MI-MII equilibrium constant, are summarized in Fig. 4. The equilibrium constant for the... 

Fig. 4. Examples of the effects of acyl chain composition (white bars) and cholesterol (gray bars) on A eq for the MI-MII equilibrium of photolyzed rhodopsin at 37°C. Higher values of correspond to higher equilibrium concentrations of Mil, the state of photolyzed rhodopsin that participates in visual signal transduction by binding the visual G protein.

Gibson NJ, Brown MF. Lipid headgroup and acyl chain composition modulate the MI-MII equilibrium of rhodopsin in recombinant membranes. Biochemistry 1993 32 2438-2454. 

Yeo YK. Philbrick DJ, Holub BJ. Altered acyl chain compositions of alkylacyl, alkenylacyl, and diacyl subclasses of choline and ethanolamine glycerophospholipids in rat heart by dietary fish oil. Biochem Biophys Acta 1989 1001 25-30. 

Once host lipid or lipid constituents are acquired, both organisms respond in a similar fashion—modification of the gross lipid composition and, in some cases, the fatty acyl chain composition of complex lipids. In most cases it is unknown why these changes are needed. The malaria parasite may be attempting to alter the permeability of the parasitized cell to allow more facile entry of nutrients. A significant part of the African typanosomes lipid metabolism is directed toward synthesis of not only membrane lipid, but supply of the glycolipid anchor of its unique surface coat. 

Because the DHA content of membrane phospholipids affects the hydration and water permeabUily of membranes (38), it is conceivable that the decrease in the proportion of DHA and other n-3 PUFA contributes to the altered phase angle we have documented in children with SCD. Our results seem to point to a link between the phase angle of an individual and the n-3 PUFA acyl chain composition of their membrane phospholipids. 

All investigated phospholipid mixtures (PC, PE, PG, PA, CL, and SM) could be easily separated by TLC and unequivocally characterized by subsequent MALDI MS. The achieved sensitivity was between 10 and 150 pmol depending on the analyte acidity, the value, and the ion polarity. The achievable lateral resolution was on the order of the laser focus diameter (about 220 x 300 j,m). This was sufficient to differentiate PL species of different acyl chain compositions within a given HPTLC spot and, thus, to provide evidence that the lipid distribution within one TLC spot is inhomogeneous. Analyte diffusion (due to the addition of glycerol to the HPTLC plate) was found to be of minor importance. Although quantitative data analysis is still the weak point of MALDI MS, these authors [30] have also shown that the... 

Whatever application route is envivioned for the liposomal drugs, according to. Ref. 409 the following quality control assays should be applied to liposomal formulations for use in humans (1) Basic characterization assays pH osmolarity trapped volume phospholipid concentration phospholipid composition phospholipid acyl chain composition cholesterol concentration active compound concentration residual organic solvents and heavy metals active compound/phospholipid ratio proton or ion gradient before and after remote loading (2) Chemical... 

Apparently the only stable component is the genetically determined protein. One plausible explanation for the control by this protein of lipid polar head composition, and for an apparent lack of control over acyl chain composition is that structurally important protein/lipid interactions occur mainly through the polar heads of the membrane lipids (Vandenheuvel, 1966). 

Without change in the composition of local lipid precursor pools the lipid composition of the membrane should remain unaltered. On the other hand, a change in acyl chain composition in the acyl chain... 

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