Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Channel former

Gomez-Puyon, A., and C. Gomez-Lojero, The use of ionophores and channel formers in the study of the function of biological membranes, in Current Topics in Bioenergetics, Vol. 6, p. 221, Academic Press, New York, 1977. [Pg.464]

A compound that binds to an ion in a manner which greatly facihtates the bound ion s permeabihty across a membrane. Naturally occurring ionophores include both mobile carriers (e.g., valinomycin and nigericin) and channel formers (e.g., gramicidin A). [Pg.376]

Table 4 lists some antibiotics that function as ionophores, including some that bind Group IIA cations. Ionophores may be classed as channel formers or carriers by several approaches. A carrier ionophore is dependent on membrane fluidity and so cannot function below the transition temperature of the phospholipids in the membrane, as these are now frozen . The channel formers are much less dependent on membrane fluidity. A channel-forming ionophore cannot function if it fails to span the membrane, and so if an ionophore ceases to function in thicker membranes then it is probably a channel former. The kinetics of ion transport may provide a good indication of the type of ionophore. If an ionophore functions at a rate of more than 104 ions s 1 then it must be a channel former, as this level of ion flux cannot be provided by the diffusion of a carrier complex across the membrane. [Pg.553]

Synthetic peptides such as (Leu-Ser-Leu-Glu)12 act as channels in artificial membranes, and reproduce the hydrophobic exterior (from leucine side chains) and hydrophilic interior (from serine hydroxyl groups) characteristic of natural channel formers. [Pg.553]

While gramicidin and other channel formers can show high transport rates, they do not show the high selectivity that characterizes natural channels. There is much interest at present in a class of proteins called porins, which form natural pores in the outer membranes of Gram-negative bacteria. Several different porin proteins have been isolated from Escherichia coli. These form water-filled channels of various sizes in membranes. Thus the proteins OmpC and OmpF seem to be cation-specific channels while other proteins give larger diameter channels that seem to be specific for anions.34,35... [Pg.553]

Cation flux rates were assessed for 10 directly in phospholipid vesicles using a dynamic 23Na NMR method. In this procedure, addition of a Dy3+ shift reagent to an aqueous vesicle solution prepared in the presence of Na+ results in an external Na+ signal shifted with respect to internal Na+. With the incorporation of a channel former, the line width broadens, reflecting dynamic exchange between internal and external Na+ through the membrane channel. Consequently, the linewidth varies directly with cation flux and a plot of [channel] versus linewidth permits determi-... [Pg.21]

Figure 15. (i) Ion-pair channel former 39. (ii) Hypothetical half-channel structure, which is connected to another similar half-channel in the other half of the monolayer. The black and white columns represent the oligoether-carboxylate anion and the two-tailed hydrophobic ammonium counter ion, respectively. Adapted version of a figure reprinted from Kohuke, Y. Morita, K., Inorg. Chim. Acta 283, 173 with permission from Elsevier Science. [Pg.37]

An indole-terminated tris(macrocycle) designed to be a channel-former and which is an effective carrier in bulk membranes but fails to function in a lipid bilayer owing to hydrogen-bond formation has been described <1996CC2147>. Tryptophan- and tryptamine-derived tetraazacyclooctadecane macrocycles have been synthesized <1996J(P1)2427>. Transannular hydrogen bonding stabilizes a left-handed double-helical conformation of the... [Pg.380]

The membrane underwent a phase transition from a highly fluid to a nearly frozen state when the temperature was lowered. A carrier can shuttle ions across a membrane only when the bilayer is highly fluid. A channel former, in contrast, allows ions to traverse its pore even when the bilayer is quite rigid. [Pg.1461]

Another system was based on a swelling core tablet and a surrounding coating consisting of a combination of hydrophobic and hydrophilic polymers. The insoluble hydrophilic polymer, such as calcium pectinate or calcium alginate, was dispersed in the coating and served as a channel-former in order to control the water penetration. The core contained a swelling, but... [Pg.1291]

Meisler The gene TCN7M (encoding the channel formerly known as Nay2.1, now known as NaJ was recently knocked out, and this affected the animal s salt intake (Watanabe et al 2000). Have you looked at that channel ... [Pg.56]

Freezing and melting of lipid bilayers greatly alters the conductance mediated by a carrier, because it influences its mobility in the membrane. In contrast, the conductance induced by a channel former is not influenced158. Similarly, an increase of the membrane viscosity, by addition of cholesterol, reduces carrier-, but not channel- mediated conductance278,217. ... [Pg.145]

Fig. 20. A model of the gating process of alamethicin-like channel formers in a membrane. Explanation in the text... Fig. 20. A model of the gating process of alamethicin-like channel formers in a membrane. Explanation in the text...
As its name implies, a carrier antibiotic must move from side to side when it shuttfes ions across a membrane. By contrast, channel formers affow ions to pass through their pores much like water through a pipe. Lowering the temperature caused a phase transition from a fluid to a nearly frozen membrane, fn the nearfy frozen state the carrier is immobifized, whereas the pore of the channel former remains intact, affowing ions to pass through it. [Pg.209]

In both cases, single-step currents occur with amplitudes ranging from about 0.2 pA to 1 nA, depending on the channel-former and the experimental conditions, especially the conductance of the membrane bathing solution. The smallest currents correspond to translocation of about 10 - 10 ions/s. A carrier diffusing back and... [Pg.109]

Figure 1.1. Structure of some channel formers valine gramicidin A (1), alamethicin (2) and... Figure 1.1. Structure of some channel formers valine gramicidin A (1), alamethicin (2) and...
The possibility of designing ion-selective channel formers, particularly when tissue selectivity based upon differing membrane lipid composition can be established, is an exciting challenge for future drug design. [Pg.10]

Triton extracts of gastric mucosa contain apparently three materials which can produce channels in lipid bilayers with conductances of 2.5 X 10 ° mho. One material is apparently neutral and cation-selective, another charged, voltage-dependent and anion-selective, whilst the third is non-selective [41]. Material which produces K -selective channels in bilayers has been extracted from excitable tissue [42]. The data obtained so far with these natural channel formers are relatively crude compared with the elegant studies with channel-fdrming antibiotics. Therefore, it is, as yet, unclear whether these materials have definitive roles in biological membrane permeability. [Pg.11]

Entropy is the major force for membrane formation. If enough elements of a membrane itself were incorporated in a model cation-channel-former, the normally feeble entropic force might assist the assembly and/or insertion process. If so, then the compound illustrated schematically could be reduced by two covalent linkages to that shown below. It, in turn, could exist in a fully extended conformation as shown. [Pg.75]

The transport of ions into or out of a cell needs to be mediated (that is, involve other species) because charged species do not partition well into the hydrophobic environment of the membrane. There are two mechanisms for ion transport mediation by a carrier molecule or transport through a channel former, a protein that creates a hydrophilic pore through which the ion can pass. An example of a channel former is the polypeptide gramicidin A, which increases the membrane permeability to cations such as ff, K+, and Na. ... [Pg.188]


See other pages where Channel former is mentioned: [Pg.569]    [Pg.570]    [Pg.553]    [Pg.9]    [Pg.10]    [Pg.20]    [Pg.23]    [Pg.30]    [Pg.32]    [Pg.553]    [Pg.683]    [Pg.1048]    [Pg.145]    [Pg.8]    [Pg.284]    [Pg.6698]    [Pg.117]    [Pg.119]    [Pg.394]    [Pg.14]    [Pg.73]    [Pg.80]    [Pg.332]    [Pg.332]   
See also in sourсe #XX -- [ Pg.188 ]




SEARCH



Former

© 2024 chempedia.info