Phospholipids, alterations

Farooqui A. A., Rapoport S. I., and Horrocks L. A. (1997). Membrane phospholipid alterations in Alzheimer disease deficiency of ethanolamine plasmalogens. Neurochem. Res. 22 523-527. 

Prasad MR, Lovell MA, Y atin M, Dhillon H, Markesbery WR. Regional membrane phospholipid alterations in Alzheimer s disease. Neurochem Res 1998 23(1) 81—88. 

Isakson, B.E. et al. Oxidized phospholipids alter vascular connexin expression, phosphorylation, and heterocellular communication. Arterioscler. Thromb. Vase. Biol. 26 (2006) 2216-21. 

Freter, C.E., R.C. Laderson, and D.F. Sibert (1979). Membrane phospholipid alterations in response to sterol depletion of LM cells. J. Biol. Chem. 254, 6909-6916. 

Farooqui AA, Rapoport SI, Horrocks LA (1997) Membrane phospholipid alterations in Alzheimer s disease deficiency of ethanolamine plasmalogens. Neurochem Res 22 523-527 Farooqui AA, Horrocks LA (1998) Lipid peroxides in the free radical pathophysiology of brain diseases. Cell Mol Neurobiol 18 599-608... 

Pettegrew, J. Panchalingam, K. Hamilton, R. McClure, R. Brain membrane phospholipid alterations in Alzheimer s disease. Neurochemical Research 2001, 26, 771-782. 

There are other ways in which the lateral organization (and asymmetry) of lipids in biological membranes can be altered. Eor example, cholesterol can intercalate between the phospholipid fatty acid chains, its polar hydroxyl group associated with the polar head groups. In this manner, patches of cholesterol and phospholipids can form in an otherwise homogeneous sea of pure phospholipid. This lateral asymmetry can in turn affect the function of membrane proteins and enzymes. The lateral distribution of lipids in a membrane can also be affected by proteins in the membrane. Certain integral membrane proteins prefer associations with specific lipids. Proteins may select unsaturated lipid chains over saturated chains or may prefer a specific head group over others. 

Cosme J, Johnson EF. Engineering microsomal cytochrome P450 2C5 to be a soluble, monomeric enzyme. Mutations that alter aggregation, phospholipid dependence of catalysis, and membrane binding. /FtoZ Chem 2000 275 2545-53. 

U shape. This has profound significance on molecular packing in membranes and on the positions occupied by fatty acids in more complex molecules such as phospholipids. Trans double bonds alter these spatial relationships. Trans fatty acids are present in certain foods, arising as a by-product of the samration of fatty acids during hydrogenation, or hardening, of natural oils in the manufacture of margarine. An additional small... 

All enveloped human vimses acquire their phospholipid coating by budding through cellular membranes. The maturation and release of enveloped influenza particles is illustrated in Fig. 3.8. The capsid protein subunits are transported flom the ribosomes to the nucleus, where they combine with new viral RNA molecules and are assembled into the helical capsids. The haemagglutinin and neuraminidase proteins that project fiom the envelope of the normal particles migrate to the cytoplasmic membrane where they displace the normal cell membrane proteins. The assembled nucleocapsids finally pass out from the nucleus, and as they impinge on the altered cytoplasmic membrane they cause it to bulge and bud off completed enveloped particles flxm the cell. Vims particles are released in this way over a period of hours before the cell eventually dies. 

In a wider context, alterations in membrane structure are generally associated with environmental stress. For example, it has been shown in the archaeon Methanococcoides burtonii that the degree of unsaturated lipids in cells grown at 4°C was higher than in cells grown at 23°C, and that the degree of unsaturation is specihc for each class of phospholipid (Nichols et al. 2004). 

Megli and Sabatini [55] studied the phospholipid bilayers after lipoperoxidation. Phospholipids were oxidized, and the oxidized phospholipid species were separated by PLC and estimated by EPR. It was shown that the early stages of lipoperoxidation brought about disordering of the phospholipid bilayer interior rather than fluidity alterations and that prolonged oxidation may result in a loss of structural and chemical properties of the bilayer until the structure no longer holds. 

De Leo, V.A., Scheide, S., Meshulam, J., Hanson, D. and Cardulla, A. (1988). Ultraviolet radiation alters choline phospholipid metabolism in human keratinocytes. J. Invest. Dermatol. 91, 303-308. 

The fate of injected liposomes is drastically altered by administration route, dose and size, lipid composition, surface modification, and encapsulated drugs. Liposomes encapsulating drugs are often administered iv, therefore, the stability of liposomes in plasma is important. When liposomes composed of PC with unsaturated fatty acyl chains are incubated in the presence of serum, an efflux of internal solute from the liposomes is observed. This increase in permeability is caused by the transfer of phospholipids to high density lipoprotein (HDL) in serum (55). To reduce the efflux of liposomal contents, cholesterol is added as a liposomal component... 

Section 3.3.4 pointed out that cosolvents alter aqueous ionization constants as the dielectric constant of the mixture decreases, acids appear to have higher pKa values and bases appear (to a lesser extent than acids) to have lower values. A lower dielectric constant implies that the force between charged species increases, according to Coulomb s law. The equilibrium reaction in Eq. (3.1) is shifted to the left in a decreased dielectric medium, which is the same as saying that pKa increases. Numerous studies indicate that the dielectric constant in the region of the polar head groups of phospholipids is 32, the same as the value of methanol. [381,446-453] Table 5.2 summarizes many of the results. 

---