Cell membrane hydrophobic

The movement of solutes from the external environment into the cell is usually achieved using cell membrane-spanning proteins that facilitate solute transfer. These are necessary, since most solutes (e.g. sugars, amino acids, salts) will not readily diffuse through the hydrophobic cell membrane. Movement of solutes into the epithelial cell can involve a variety of protein carriers or channels including (see Figure 1) ... 

It has been emphasized in the previous paragraphs that effecting the through-membrane transport of artificial antiviral nucleotide analogs would be beneficial in that it might allow the direct into-cytoplasm entry of species that would be otherwise inactive in vivo (due to an inability to cross hydrophobic cell membranes). Within the overall scope of this problem, finding ways to effect the into-cell transport of nucleotide di- and triphosphates is deemed particularly important. This is because it is often these forms that are the most potent. 

Most of the nucleic acid model compound prepared so far are water insoluble however, when the analogs are water soluble, they may not permeate into the hydrophobic cell membranes. Recently, an improved drug delivery system for water soluble drugs using polysaccharide-coated liposomes [68] was developed. 

Steroid receptors are an exception to the general rule that receptors are memhrane proteins. Steroid receptors are normally present as soluble proteins in the cytoplasm. Steroids diffuse across the hydrophobic cell membrane and bind to their specific receptors. The receptors then translocate to the nucleus by simple diffusion, where they act as transcription factors by binding to specific regions of chromosomal DNA (steroid response elements), thus controlling transcription of particular genes. 

Water-soluble vitamins are forced to cross a formidable barrier during absorption—the hydrophobic cell membrane. Three possible mechanisms, which enable riboflavin translocation, are suggested. Two of these mechanisms, a saturable, carrier-mediated process and receptor-mediated endocytosis, occur at the physiological concentration of riboflavin the third one, passive diffusion, is exploited at higher concentrations of the vitamin (Ball 2004a). 

The major stmctural feature of the HAz chain (blue in Figure 5.20) is a hairpin loop of two a helices packed together. The second a helix is 50 amino acids long and reaches back 76 A toward the membrane. At the bottom of the stem there is a i sheet of five antiparallel strands. The central i strand is from HAi, and this is flanked on both sides by hairpin loops from HAz. About 20 residues at the amino terminal end of HAz are associated with the activity by which the vims penetrates the host cell membrane to initiate infection. This region, which is quite hydrophobic, is called the fusion peptide. 

Cell membrane The cell membrane is composed of about 45% lipid and 55% protein. The lipids form a bilayer that is a continuous nonpolar hydrophobic phase in which the proteins are embedded. The cell membrane is a highly selective permeability barrier that controls the entry of most substances into the cell. Important enzymes in the generation of cellular energy are located in the membrane. 

We modified polyanionic polymers by use of a grafting reaction of hydrophobic groups onto the polymers. After an extensive evaluation for the affinity of the hy-drophobically modified (hydrophobized) polymers to cell membrane, the immuno-stimulating activity of polymers was investigated by in vitro or ex vivo experiments. Consequently, the increased biological activity was found in the hydrophobized polymer, indicating that... 

Two hydrophobized polymers, MA-DP-A20 (phenyl group grafted in 20 mol%) and MA-DP-H68 (hexyl group grafted in 68 mol%), were selected for the evaluation of the interaction between polymers and cell membranes... 

The in situ method using rat living intestine was simple and qualitative. However, it was difficult to evaluate the weak interaction between polymers and cell membranes quantitatively. Therefore, the lipid bilayer of liposome was used as a model of cell membranes for the quantitative evaluation for the affinity of the hydrophobized polymers (15). 

Based on the data in Figs. 2 and 4, it appears that the affinity of the polyanionic polymer for cell membrane can be increased by the hydrophobization of polymers. 

There was no distinct difference between polymers having different molecular weights. From the data in Figures 2, 4, 5, and 6, it seems to be established that the affinity of polyanionic polymers for cell membrane is adjustable by a simple grafting of hydrophobic groups. 

A large number of combinations are theoretically possible and a lot of these structures are actually used in practice. We know that nature makes use of this variety, e.g., to form cell membranes by phospholipids. However, in daily practice the pool of hydrophobic raw material for the production of anionic phosphorus-containing surfactants is survey able. 

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