Cell-surface membranes

Vaz WLC, Derzko ZI, Jacobson K. Photobleaching measurements of the lateral diffusion of lipids and proteins in artificial phospholipid bilayer membranes. Cell Surface Rev. 1982 8 83-135. 

Clathrin vesicles transport proteins from the plasma membrane (cell surface) and the trans-Golgl network to late endosomes. 

IgD Monomer ECF+cell membrane Cell surface antigen receptors... 

B Alpha Beta Aipha/Beta B Alpha+Beta B Multidomain s Membrane Cell surface Small... 

The primary site of action is postulated to be the Hpid matrix of cell membranes. The Hpid properties which are said to be altered vary from theory to theory and include enhancing membrane fluidity volume expansion melting of gel phases increasing membrane thickness, surface tension, and lateral surface pressure and encouraging the formation of polar dislocations (10,11). Most theories postulate that changes in the Hpids influence the activities of cmcial membrane proteins such as ion channels. The Hpid theories suffer from an important drawback at clinically used concentrations, the effects of inhalational anesthetics on Hpid bilayers are very small and essentially undetectable (6,12,13). 

Biochemically, most quaternary ammonium compounds function as receptor-specific mediators. Because of their hydrophilic nature, small molecule quaternaries caimot penetrate the alkyl region of bdayer membranes and must activate receptors located at the cell surface. Quaternary ammonium compounds also function biochemically as messengers, which are generated at the inner surface of a plasma membrane or in a cytoplasm in response to a signal. They may also be transferred through the membrane by an active transport system. 

The mechanism of inhibition has not been characterized, but it is probably related to the ionophoretic properties of these antibiotics. Monensin has been shown to inhibit the intracellular transport of viral membrane proteins of cells infected with Semliki Forest vims (169). The formation of syncytia, normally observed when T-lymphoblastoid cell line (CEM) cells are cocultivated with human immunodeficiency vims (HlV-l)-infected T-ceU leukemia cell line (MOLT-3) cells, was significantly inhibited in the presence of monensin (170). This observation suggests that the viral glycoproteins in the treated cells were not transported to the cell surface from the Golgi membrane. 

Considerable work has been done to try to explain why quats are antimicrobial. The following sequence of steps is beheved to occur in the attack by the quat on the microbial cell (/) adsorption of the compound on the bacterial cell surface (2) diffusion through the cell wall (J) binding to the cytoplasmic membrane (4) dismption of the cytoplasmic membrane (5) release of cations and other cytoplasmic cell constituents (6) precipitation of cell contents and death of the cell. 

Class 1 and class II MHC molecules bind peptide antigens and present them at the cell surface for interaction with receptors on T cells. The extracellular portion of these molecules consists of a peptide-binding domain formed by two helical regions on top of an eight-stranded antiparallel p sheet, separated from the membrane by two lower domains with immunoglobulin folds. These domains are differently disposed between the two protein subunits in class I and class II molecules. 

Structure of Membrane Protein.s Membrane and Cell-Surface... 

The completed exopolysaccharide is then transported to the cell surface through membrane adhesion zones. 

The steroid hormone 1,25-dihydroxy vitamin D3 (calcitriol) slowly increases both intestinal calcium absorption and bone resorption, and is also stimulated through low calcium levels. In contrast, calcitonin rapidly inhibits osteoclast activity and thus decreases serum calcium levels. Calcitonin is secreted by the clear cells of the thyroid and inhibits osteoclast activity by increasing the intracellular cyclic AMP content via binding to a specific cell surface receptor, thus causing a contraction of the resorbing cell membrane. The biological relevance of calcitonin in human calcium homeostasis is not well established. 

Caveolae are invaginations of the plasma membrane. They contain the protein caveolin and are rich in certain phospholipids. Similar to coated pits, they bud off internally forming endocytic vesicles. Caveolae play an important role in the internalization of certain cell surface receptors. 

The ECE isoforms show different subcellular distributions and enzymatic characteristics (Table 2). ECE-la and ECE-lc are mainly expressed at the cell surface, whereas ECE-lb, ECE-Id and ECE-2 are expressed intracellularly. Plasma membrane-bound ECE cleaves big-ET-1 circulating in the blood, whereas intracellular ECE isoforms are involved in the generation of mature endothelins. In addition, ECEs (as well as NEP and the insulin-degrading enzyme) contribute to the degradation of amyloid (3 (A 3) peptide. 

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