Hydrophilic pathways

Stahl, C., Kubetzko, S., Kaps, I., Seeber, S., Engelhardt, H. and Niederweis, M. (2001). MspA provides the main hydrophilic pathway through the cell wall of Mycobacterium smegmatis, Mol. Microbiol., 40, 451-464. 

We assume that all substances involved in ferritin iron deposition (Fe2+, Fe3+, 02) need to gain access to the interior of the apoferritin protein shell. The most likely pathway is via the three-fold channels, which would involve passing through the 12 A long channel, and then traverse a further distance of 8 A along a hydrophilic pathway from the inside of the... 

Some natural ion channels are believed to form amphiphilic a-helix bundles in hydrophobic lipid membranes, where the a-helices assemble with their hydrophilic parts facing each other, resulting in a hydrophilic channel. If artificial peptides that had appropriate combinations of both hydrophobic amino acid residues and hydrophobic amino acid sequences were used, the peptides would self-assemble to form a hydrophilic pathway in the lipid membrane. 

The mechanism of action of disintegrating agents has been the subject of some debate. Some substances such as starch swell when they come into contact with water, and disruption of the tablet structure has been attributed to this. However, other effective disintegrants do not swell in this way, and are believed to act by providing a network of hydrophilic pathways inside the tablet through which water can diffuse. Irrespective of the precise mechanism of disintegration, it is clear that water uptake into the tablet must be the first step in the disintegration process. ... 

Fe(II) must then move from the 12 A long channel, and traverse a further distance of about 8 A along a hydrophilic pathway from the inner side of the three-fold channel to the ferroxidase site, and a putative pathway for Fe(II) is shown in Figure 19.6. The diiron ferroxidase centre is located in the central region of the four-helix subunit bundle and the coordination geometry of the ferroxidase centre of human H-chain ferritin is shown in Figure 19.7. Detailed analysis of the ferroxidase reaction in H-chain ferritin has allowed the identification of a number of intermediates, which are illustrated in Figure 19.8. 

Pressure waves (PW), which can be generated by intense laser radiation, without incurring direct ablative effects on the skin have also been recently found to increase the permeability of the skin [66-68]. It is thought that PW form a continuous or hydrophilic pathway across the skin due to expansion of the lacunae domains in the SC. Important parameters affecting delivery such as peak pressure. 

The lipid-soluble anesthetic molecules, on the other hand, diffuse across the neuronal membrane in their un-ionized forms. They can interact with the same receptors from either the hydrophilic pathway (pathway b in Fig. 16.7) on reprotonation to their onium ions [BH + ] or via the hydrophobic pathway (pathway a in Fig. 16.7) in their un-ionized forms [B]. Benzocaine and other nonbasic local anesthetic molecules use this hydrophobic pathway and, thus, bind to the same receptor, although at the hydrophobic site of the receptor, to produce their actions. Again, this... 

Fig. 16.7. Model of a sodium channel, as suggested by Hille (34), depicting a hydrophilic pathway (denoted by b and b ) and a hydrophobic pathway (denoted by a) by which local anesthetics may reach their receptor sites.

Fig. 2. Schematic representation of two possible models which may give rise to the apparent presence of hydrophilic pathways for water transport in human red-cell membrane. In Fig. 2A on the left, the pores are assembled from membrane integral proteins which are aggregates of identical or nonidentical sub-units. In Fig. 2B on the right, water molecules move across the membrane by jumping into the free volume (kinks) generated by the thermal fluctuations in membrane lipid. (From (4).)...

In buffer medium, the CT-NajCit entrapped in CAc polymer would absorb water, swell and, consequently, create hydrophilic pathways that should facilitate the release of the drug. CT-NajCit-CAc has moderate release in both pH values, 64.8% (pH7.4) and 53.0% (pH 1.8). The complex coating not only limits the erosion of CT matrix but also retards initial drug release. The results show that a coating on CT-NajCit causes a delayed delivery of drug in gastric pH. These results show that there is no remarkable difference in dissolution characteristics at different pH values by CAc coating. Similar result was obtained for the release of ranitidine chloride from CAc/ CT microsphere [14]. 

A set of microposts made of pH-responsive hydrogel was constructed in a microfluidic chamber. A circular aperture was formed in a flexible polymer slip. The sidewall and top side of the aperture were treated to be hydrophilic and hydrophobic, respectively. Again, since aqueous solutions remained only on hydrophilic pathways at pressures below a critical value, part of the water-based liquid attached to the sidewall could form a liquid meniscus protruding downward at low pressures and upward at high pressures. 

The membrane domain of the enzyme contains the ion-transport pathways. There must be a hydrophilic pathway in the membrane domain that the ions can traverse as the cytoplasmic domain changes conformation as a function of phosphorylation and dephosphorylation. 

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