Cation-proton transport

To ensure the specificity of the signal, it will always be very helpful to test a unique feature of the carrier under investigation, such as specific inhibition, dependence on anions/cations/protons or trans-activation by another substrate. Sodium dependency, for example, can be tested by replacement with N-methyl-D-glucamine, whereas choline chloride as substitute of sodium is not recommended, since it may influence the membrane potential. In light of the recent finding that many transport proteins display an overlapping substrate spectrum, such specificity controls should receive adequate appreciation. 

A second important application of CMD has been to study the dynamics of the hydrated proton. This study involved extensive CMD simulations to determine the proton transport rate in on our Multi-State Empirical Valence Bond (MS-EVB) model for the hydrated proton. = Shown in Fig. 4 are results for the population correlation function, (n(t)n(O)), for the Eigen cation, HsO, in liquid water. Also shown is the correlation function for D3O+ in heavy water. It should be noted that the population correlation function is expected to decay exponentially at long times, the rate of which reflects the excess proton transport rate. The straight line fits (dotted lines) to the semi-log plots of the correlation functions give this rate. For the normal water case, the CMD simulation using the MS-EVB model yields excellent agreement with the experimental proton hopping... 

The ionophores have been incorporated into the vesicle membranes and cation flux was assessed either by monitoring the fluorescence of pyranine dye encapsulated within vesicles for estimating the proton transport rate or by analyzing the line shape of Na nucleus by NMR spectroscopy to evaluate the flux rate of Na+ 106-110 Qf ionophores were expressed by percent activity relative... 

Organic cation transporters OCT SLC22A2/3 Luminal Blood to endothelium Organic cation/proton exchange... 

The protons are dissociated away in contact with the water in the internal channels. Center. A covalent bonding of proton donor-acceptor molecules and a sufficiently dense stacking leads to a solvent free proton transport. Bottom. In the soggy sand electrolytes anions are absorbed at the surfaces of the insulating matrix (e.g., SiOJ. The respective cations (e.g., Li+) are free while far away from the matrix essentially associated in form of ions pairs if the solvent is a weak dielectric. 

Using the principle of ion pair formation between ammonium cations and the phosphate anions of lipids, Matile et al.33 prepared 8, an amphiphilic polyamine dendrimer. Rather than acting as a membrane channel, 8 was expected to form reversible membrane defects in the lipid bilayer. The steroid moiety was expected to act as the hydrophobic anchor for bilayer orientation and steric bulk was expected to prevent the polyamine penetrating the bilayer. Proton transport was assessed in unilamellar vesicles using the pH-fluorescence technique in which the external pH was increased to 7.8 relative to the internal pH at 7.4. The results demonstrated that 8 was almost as active as gramicidin, and maximal flux was achieved in ca. 20 s. 

The efflux from cell to lumen is the active step of organic cation secretion transport being against the transmembrane potential. This active transport occurs through an exchange with protons (mechanism... 

Pyles TM, mcMalik-Diemer VA, McGavin CA, Whitfield DM, Membrane transport systems. III. A mechanistic study of cation-proton coupled countertransport. Can. j Chem. 1982 60, 2259. 

---