No abstract

The functional consequences of single proton transfers occurring in the pore of a cyclic nucleotide-gated channel were observed with patch recording techniques. These results led to three conclusions about the chemical nature of ion binding sites in the conduction pathway: The channel contains two identical titratable sites, even though there are more than two (probably four) identical subunits; the sites are formed by glutamate residues that have a pKa (where K(a) is the acid constant) of 7.6; and protonation of one site does not perturb the pKa of the other. These properties point to an unusual arrangement of carboxyl side-chain residues in the pore of a cation channel.

Die Redoxeigenschaften und die spektralen Eigenschaften der cis‐Ru‐Komplexe (I) und der cis‐Os‐Komplexe (II) werden im Hinblick auf den relativen n‐Säure‐Charakter der S‐, N‐, P‐enthaltenden Liganden sowie der Halogenidliganden rationalisiert.

This study investigates the influence of a through-solution electrostatic interaction on the kinetics of ion channel blockade by the high-affinity peptide inhibitor Lq2. Membrane patches containing many Shaker K+ channels were removed from Xenopus oocytes and placed in a rapid perfusion chamber. Lq2 association and dissociation rate constants were determined from the relaxations to equilibrium blockade following rapid changes in toxin concentration. The association and dissociation rate constants were 8.5 x 10(7) M-1 s-1 and 0.71 M-1 s-1, respectively, in 100 mM NaCl solution, pH 7.1, at room temperature (21-23 degrees C). Charge-altering mutations introduced at position 422 on the ion channel affect toxin affinity in a manner consistent with a through-solution electrostatic interaction. The full effect of the charge mutations is expressed kinetically on the association rate; toxin dissociation remains unaltered. An electrostatic influence on the association rate alone is expected if diffusion of toxin up to (and away from) its receptor on the channel is fast compared to the rate of formation of short-range contacts that are necessary to produce the bound state.

International audienceA series of carbon fluorine compounds (C_xF) was prepared by catalyzed, room-temperature reactions of natural graphite, petroleum coke, and coal-tar-pitch coke with fluorine in the presence of HF and IF₅. Elemental analysis indicated that most of the compounds had carbon-to-fluorine ratios between 1 and 2. X-ray diffraction, X-ray photoelectron spectroscopy, and infrared spectroscopy suggest that carbon-fluorine bond strengths were intermediate between ionic and covalent. The C_xF materials exhibit higher reduction potentials when compared to commercially available CF_x. Although the discharge capacities were lower for C_xF compounds, their greater discharge voltage yielded higher energy densities than for analogous CF_x cells. Discharge capacities for C_xF increased slightly when prepared from petroleum coke heated to 1700°C compared with coke heated to 2600°C. This suggests that better discharge performance may be achieved from carbons with lower degrees of graphitization. C_xF synthesized from natural graphite with particle sizes <10 µm had a greater discharge capacity on a mass basis but a lower discharge efficiency based on F content when compared to C_xF prepared from natural graphite with particle sizes between 20 and 40 µm. Materials prepared from coal-tar-pitch coke exhibited poor discharge capacities