Potassium ion and protons

Active pH homeostasis depends primarily on the potassium ion and proton circuits. The genetic control of ATR in S. typhimurium consists of two stages, the preacid-shock phase and the postacid-shock phase. The preacid shock is induced at an external pH of pH 5.8, and the postacid shock... 

Under these conditions, a typical measured proton flux might be in the range of 10 15 mol/(cm2 s). To compare this value with that of potassium, 1 M potassium ion (as potassium sulfate) could be trapped inside the same liposomes, and potassium efflux into 1 M choline sulfate could be measured with a potassium-sensitive electrode. A typical result might again be in the range of 10 15 mol/(cm2 s). The proton permeability anomaly now becomes clear The same flux is measured for both potassium ion and protons, yet the proton flux is driven by a concentration of protons 6 orders of magnitude less than the concentration of potassium ions. Estimates of the relative permeabilities of the bilayer to protons and potassium using these flux data yield values of 10 6 cm/s for protons and 10 12 cm/s for potassium ion. 

Wolf and Schwieger [65] described the exchange of sodium ions of the Her silicate by potassium ions and protons as well as the exchange of magadiite sodium ions by potassium ions, lithium ions, and protons. The diagrams in Figure 16 clearly show the selectivity for sodium versus lithium and potassium ions i.e., the equivalent fraction of the lithium and potassium ions on the silicate is... 

We investigate the problem of establishing a concentration gradient, say across a membrane. This establishment requires energy, for example from ATP. In turn the gradient may be used to do work in the surroundings of the system. The subject is closely related to the issue of the efficiency of biological pumps, such as pumps for sodium ions, potassium ions, and protons. 

Paula, S., Volkov, A. G., van Hoek, A. N., Haines, T. H. and Deamer, D. W. (1996). Permeation of protons, potassium ions, and small polar solutes through phospholipid bilayers as a function of membrane thickness, Biophys. J., 70, 339-348. 

Fig.1 Schematic structures of a DNA, b butynedioic acid and c KDP. Large striped circles represent potassium ions and medium filled circles oxygen ions. Small filled circles are protons and checkerboard filled circles represent phosphorous ions, d Schematic structure of squaric acid...

Lehn and coworkers have profitably employed tartaric acid-containing crown ethers as enzyme models. The rate of proton transfer to an ammonium-substituted pyridinium substrate from a tetra-l,4-dihydropyridine-substituted crown ether was considerably enhanced compared to that for a simple 1,4-dihydropyridine. The reaction showed first order kinetic data and was inhibited by potassium ions. Intramolecular proton transfer from receptor to substrate was thus inferred via the hydrogen bonded receptor-substrate complex shown in Figure 16a (78CC143). 

Ionized forms of molecules are nearly always accompanied by counterions of the opposite charge. When the counterion is a proton, the ion and proton complex is called an acid. When the counterion is a different cation, such as a sodium, potassium, or ammonium ion, the complex is called a salt-... 

Active pH homeostasis Depends primarily on the potassium ion and the proton circuits. 

The data from both neutron and x-ray diffraction agree on the above structural aspects as well as the location of the potassium ions and three water sites for 4b but differ in the location of the bromide ions and the occupancy of an anomalous site ( in Fig. 29) located near the center of the unit cell (60% occupied by the bromide ion). Williams et al. (574) claim that the site is a disordered bromide site, such that 25 % of the unit cells have a bromide ion occupying this site instead of the usual position (O in Fig. 29). Recent low temperature (77° K) neutron diffraction data agree with this assignment as protons... 

The basic features of a cell membrane are given in Figure 1 to show how it consists essentially of protein molecules incorporated into a semifluid liquid bilayer structure. As a rough guide the plasma membrane of most cells is composed, on a dry weight basis, of nearly equal components of protein and lipid. Because of its nonpolar nature the lipid membrane structure is intrinsically impermeable to polar and electrically charged molecules. For example, turbidity measurements on sarcoplasmic reticulum membranes provide membrane resistance values of 2.6 x 10 and 2.5 X 10 Q cm for the permeability of calcium ions and protons, respectively, while for sodium and potassium ions the corresponding values are... 

F. IS. Exchange of internal potassium ions for external sodium ions and protons catalyzed by nigericin, 10 pM/ml, applied to a suspension of human erythrocytes (10% packed cell volume). The changes in the concentration of sodium, potassium and hydrogen ions were monitored by ion specific electrodes. Movement of ions from the cells into solution is shown by a downward deflection... 

Potassium Phosphates. The K2O—P20 —H2O system parallels the sodium system in many respects. In addition to the three simple phosphate salts obtained by successive replacement of the protons of phosphoric acid by potassium ions, the system contains a number of crystalline hydrates and double salts (Table 7). Monopotassium phosphate (MKP), known only as the anhydrous salt, is the least soluble of the potassium orthophosphates. Monopotassium phosphate has been studied extensively owing to its piezoelectric and ferroelectric properties (see Ferroelectrics). At ordinary temperatures, KH2PO4 is so far above its Curie point as to give piezoelectric effects in which the emf is proportional to the distorting force. There is virtually no hysteresis. 

Three kinds of equilibrium potentials are distinguishable. A metal-ion potential exists if a metal and its ions are present in balanced phases, e.g., zinc and zinc ions at the anode of the Daniell element. A redox potential can be found if both phases exchange electrons and the electron exchange is in equilibrium for example, the normal hydrogen half-cell with an electron transfer between hydrogen and protons at the platinum electrode. In the case where a couple of different ions are present, of which only one can cross the phase boundary — a situation which may exist at a semiperme-able membrane — one obtains a so called membrane potential. Well-known examples are the sodium/potassium ion pumps in human cells. 

Potentiometry (discussed in Chapter 5), which is of great practical importance, is a static (zero current) technique in which the information about the sample composition is obtained from measurement of the potential established across a membrane. Different types of membrane materials, possessing different ion-recognition processes, have been developed to impart high selectivity. The resulting potentiometric probes have thus been widely used for several decades for direct monitoring of ionic species such as protons or calcium, fluoride, and potassium ions in complex samples. 

One may conclude that a particle monolayer is actually formed at each pH value of the subphase, only if care is taken that the sum concentration of protons and metal (e.g., potassium) ions in the subphase, Ch + Ck, is constant. This is actually true, as shown in Figure 7, where the Aq-value of a monolayer of particles la is plotted against the pH of the subphase at constant sum concentration of H and of 1 mol 1 [77]. 

FIG. 7 Plot of the limiting area, Aq, of anionic particles la against the pH of the aqueous subphase, with the sum concentration of protons and potassium ions in the subphase being kept constant at 1 mol... 

Other reactions in which cations other than protons are catalyti-cally effective are esterification and acetal formation, catalyzed by calcium salts,277 and the bromination of ethyl cyclopentanone-2-carboxylate, catalyzed by magnesium, calcium, cupric, and nickel, but not by sodium or potassium ions.278 One interpretative difficulty, of course, is the separation of catalysis from the less specific salt effects. The boundary line between salt effects (medium effects) and salt effects (catalysis) is not sharp either in concept or experimentally. 

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