Channels in membranes

Urry, D. W. On the Molecular Structure and Ion Transport Mechanism of the Gramicidin Transmembrane Channel. In Membranes and Transport, Vol. 2, (ed. Martonosi, A.), p. 285, Plenum Publishing Corporation, New York 1982... 

Channel-forming toxins and antibiotics. Some of the bacterial toxins known as colicins (Box 8-D) kill susceptible bacteria by creating pores that allow K+ to leak out of the cells. One part of the complement system of blood (Chapter 31) uses specific proteins to literally punch holes in foreign cell membranes. Mel-litin, a 26-residue peptide of bee venom,372 373 as well as other hemolytic toxins and antibiotic peptides of insects, amphibians, and mammals (Chapter 31) form amphip-athic helices which associate to form voltage-dependent anion-selective channels in membranes.374-377... 

The important bacterial storage material poly-hydroxybutyric acid is related metabolically and structurally to the lipids. This highly reduced polymer is made up of D-(3-hydroxybutyric acid units in ester linkage, about 1500 residues being present per chain. The structure is that of a compact right-handed coil with a twofold screw axis and a pitch of 0.60 nm.a Within bacteria it often occurs in thin lamellae 5.0 nm thick. Since a chain of 1500 residues stretches to 440 nm, there must be 88 folds in a single chain. Present in both cytoplasmic granules and in membranes,b polyhydroxybutyrate can account for as much as 50% of the total carbon of some bacterial In E. coli and many other bacteria polyhydroxybutyrate is present in a lower molecular mass form bound to calcium polyphosphates, proteins, or other macromolecules.d e It has also been extracted from bovine serum albumin and may be ubiquitous in both eukaryotes and prokaryotes.d/e The polymer may function in formation of Ca2+ channels in membranes.b/d... 

Figure 4 Schematic representation of gramicidin channels in membranes...

The development of biophysical techniques to make possible measurements of single ion channels in membrane bilayers has been fundamental to the advances in the understanding of how natural ionophores, particularly ion channel proteins, operate at the molecular level. The two principal techniques are the planar lipid... 

Opening "gates" of calcium channels in membranes of the ER or of calciosomes. If diffuses across the peripheral cytoplasm to InsPg receptors which are embedded in the membranes of fhe One of... 

It is a general property of internalized toxins and certain viruses that they form channels in membranes. The portion of the toxin molecule associated with channel formation is typically the same as that needed for internalization. This could mean that channel formation is the mechanism that underlies translocation, or that it is an epiphe-nomenon that occurs coincidentally with translocation. In either case,... 

Fig. 23. Visualization of membrane fouling by scanning electron microscopy (A) inorganic fouling dne to calcinm carbonate, calcium sulfate, silica, iron, barium and strontium sulfate (35,000x) (B) organic fonling dne to humic acid (35,000x) (C) flow channels in membrane fouled with biological growth.

Nandsi PP, VarrO A, Lathrop DA, Bryant SH (1994) Effects of veratridine on Na and Ca currents in frog skeletal muscle. Gen Pharmacol 25 1661-1666 Naumov AP, Negulyayev YuA, Nosyreva ED (1979) Change of selectivity of sodium channels in membrane of nerve fiber treated with veratrine (in Russian). Tsitologiya 21 692-696... 

Figure 3c shows a potential energy profile sequence that accentuates the normal inward rectification the reason is that [Na+] is high and entry is easy (barrier is low) from the outside and vice versa on the inside. I know of no examples of this behavior in a cell membrane. The delayed rectification of a K+ channel in membranes of squid nerve fibers is of this nature (N process in Fig. 2) but this is undoubtedly due to the opening of more channels rather than the property of a single channel. As mentioned above, the instantaneous current-voltage relation of an open K+ channel is linear. The theory developed here, however, is not directly applicable to K+ channels since the independence assumption does not hold for K+ channels. 

This method relies on the simple principle that the flow of ions into an electrolyte-filled micropipette as it nears a surface is dependent on the distance between the sample and the mouth of the pipette [211] (figure Bl.19.40). The probe height can then be used to maintain a constant current flow (of ions) into the micropipette, and the technique functions as a non-contact imaging method. Alternatively, the height can be held constant and the measured ion current used to generate the image. This latter approach has, for example, been used to probe ion flows through channels in membranes. The lateral resolution obtainable by this method depends on the diameter of the micropipette. Values of 200 nm have been reported. 

We now know a great deal about the structure of cell membranes, ion pumps, electroporation, and membrane channels. In membrane reconstitution experiments, the evidence is that intracellular signal transduction begins at membrane receptors. The work... 

The search for biologically active compounds (natural and synthetic) continued to be a significant inspiration for organic synthesis. Asymmetric catalysis, new synthetic reactions, and advances in separation techniques (HPLC) and analytical techniques (NMR and mass spectrometry) support these advances. In 1995, Kyriacos Costa (K.C.) Nicolaou (1946- ) at Scripps Research Institute reported the total synthesis of brevetoxin B (see the figure on page 375). This toxic substance is produced by algae in red tide and is very deadly to fish. It binds to sodium channels in membranes of muscle and nerve cells producing an excessive influx of Na. ... 

Fig. 5 Examples of systems able to form channels in membranes. Left the Ghadiri s self-assembled nanotube formed by cyclopeptides. Right The Voyer s 21 amino acid peptide containing six 21-crown-7 L-phenylalanines. In a membrane, the peptide adopts an a-helical conformation that allows the partial alignment of the macrocycles, one over the other.

The mellitin tetramer forms a voltage-dependent chloride channel in membranes. Your calculations might allow you to study the gating mechanism which controls chloride passage. 

Li, X.X., Davis, B., Haridas, V., Gutterman, J.U., and Colombini, M. (2005b) Proapoptotic triter-pene electrophiles (avicins) form channels in membranes cholesterol dependence. Biophys J 88 2577-2584. 

Ganfornina MD, Lopez-Bameo J. Single K channels in membrane patches of arterial chemoreceptor cells are modulated by O2 tension. Proc Natl Acad Sci LISA 1991 88(7) 2927-2930. 

Siskind LJ, Fluss S, Bui M, Colombmi M. Sphingosine forms channels in membranes that differ greatly from those formed by ceramide. / Bioenerg Biomembr. 2005 37(4) 227-236. 

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