Membranes polymorphism

From Giant Micelles to Fluid Membranes Polymorphism in Dilute Solutions of Surfactant Molecules... 

Figure 15.18 (a) Schematic representation of the path of the polypeptide chain in the structure of the class I MHC protein HLA-A2. Disulfide bonds are indicated as two connected spheres. The molecule is shown with the membrane proximal immunoglobulin-like domains (a3 and Pzm) at the bottom and the polymorphic al and a2 domains at the top. 

The seminal work by early transplant researchers eventually led to the concept of histocompatibility.1,2 Histocompatibility describes the process where polymorphic genes encode cell membrane antigens that serve as targets for immune response, even within a species. Further research in transplant immunobiology has led to an accurate understanding of the immune response after transplantation.1,2... 

This chapter describes some of the properties of solids that affect transport across phases and membranes, with an emphasis on biological membranes. Four aspects are addressed. They include a comparison of crystalline and amorphous forms of the drug, transitions between phases, polymorphism, and hydration. With respect to transport, the major effect of each of these properties is on the apparent solubility, which then affects dissolution and consequently transport. There is often an opposite effect on the stability of the material. Generally, highly crystalline substances are more stable but have lower free energy, solubility, and dissolution characteristics than less crystalline substances. In some situations, this lower solubility and consequent dissolution rate will result in reduced bioavailability. 

Recently, the presence of single nucleotide polymorphisms (SNPs) has been reported for several types of transporter. Extensive studies have been performed on the SNPs of OATP2 [100, 101], and the SNPs identified in African- and European-Americans are indicated in Fig. 12.3. Moreover, the frequency of SNPs differed among the African-American, European-Americans and Japanese, indicating the presence of an ethnic difference in the allelic mutation of this transporter [100, 101]. In addition, some of the mutations were associated with reduced transporter function and/or abnormalities in membrane targeting [100, 102] (Fig. 12.3). It is... 

Fig. 2.4. Schematic model of the molecular polymorphism of acetylcholinesterase and cholinesterase [110][112a]. Open circles represent the globular (G) catalytic subunits. Disulfide bonds are indicated by S-S. The homomeric class exists as monomers (Gl), dimers (G2), and tetramers (G4) and can be subdivided into hydrophilic (water-soluble) and amphiphilic (membrane-bound) forms. The G2 amphiphilic forms of erythrocytes have a glycophospholipid anchor. The heteromeric class exists as amphiphilic G4 and as asymmetric forms (A) containing one to three tetramers. Thus, heteromeric G4 forms found in brain are anchored into a phospholipid membrane through a 20 kDa anchor. The asymmetric A12 forms have three hydrophilic G4 heads linked to a collagen tail via disulfide bonds.

CuUis, P.R., and de Kruiff, B., 1997, Lipid polymorphism and the functional roles oflipids in biological membranes, Biochim. Biophys. Acta 559 399-420. 

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