Calcium transport properties

The discovery of the calcium-transporting properties of lasalocid and A-23187 has prompted numerous studies concerning their physiological activities they were shown to be potential cardiovascular agents. Although clinical apph-cations have been hampered by their potential toxicity, almost all of these antibiotics have become particularly important as coccidiostatics for poultry industries. 

It would be preferable to incorporate both fluorescent and electron transport properties in the same material so as to dispense entirely with the need for electron-transport layers in LEDs. Raising the affinity of the polymer facilitates the use of metal electrodes other than calcium, thus avoiding the need to encapsulate the cathode. It has been shown computationally [76] that the presence of a cyano substituent on the aromatic ring or on the vinylene portion of PPV lowers both the HOMO and LUMO of the material. The barrier for electron injection in the material is lowered considerably as a result. However, the Wessling route is incompatible with strongly electron-withdrawing substituents, and an alternative synthetic route to this class of materials must be employed. The Knoevenagel condensation... 

Nerve growth factor snake venoms zinc, 6, 613 Neurospora crassa calcium transport, 6, 571 cation transport, 6, 559 Neurosporin, 6, 676 Neurotransmitters secretion calcium, 6, 595 Neutral complexes electrical properties, 6, 143 Neutron absorbers... 

The ion selectivities displayed by these antibiotics are lower than those of the neutral ionophores, and are given in Table 11. Many studies have been made on the properties of these ionophores, particularly with reference to the calcium-transporting abilities of A 23187 (146) and lasolocid (145). The search for new antibiotics is ongoing and there is constant addition to a list of about 50 distinct polyether antibiotics which have been isolated from various streptomycetes. Representative structures will be discussed here to illustrate the nature of complexation with alkali and alkaline earth metal cations. 

Fat or lipid materials and calcium-lipid complexes also contribute to fouling and flux decline in membrane processing of milk or whey. The transport properties of the feed stream and the changes they undergo as the concentration process proceeds also affect the rate of permeation. At high concentrations, the increased fluid viscosity near the membrane surface limits back-diffusion of solids from the polarized layer to the bulk phase, thereby, depressing flux rate [46]. 

The system 8a La Cu Q chosen by Bednorz and Muller (1) for their first investigation of superconductivity was connected to the existence of metallic properties of the oxide BaLa CusOis+s recently isolated in Caen (2). However the method used for the synthesis did not lead to the expected oxide but to a mixture of phases. Fortunately, one of these latter phases was found to be at the origin of superconductivity. In fact the concerned oxide is a M liF -type oxide, La2-xBaxCu04-y, isolated and studied for its electron transport properties several years before in Caen (3-4). It was then shown by several authors (5-9) that the strontium isostructural oxide La2-xSrxCu04-y (10-11) and the calcium compound (3-4) were also superconductors with Tc values ranging form 20K to 40K. 

Royce, B.S.H. (1973) The effect of structure and ionic transport properties of calcium apatite. /. Rhys. Suppl., 34, 327-332. 

Figure 5.5 Transport properties of a cation exchange membrane having a cationic polyelectrolyte layer formed by electrodeposition. (A) PNaCa ( ) current efficiency (%) ( ) electrical resistance of the membrane during electrodialysis for 1 h. After solutions containing 0.0416N sodium chloride and poly(3-methylene-N, N-dimethylcyclohexylammonium chloride) of various concentrations had been electrodialyzed, for 60 min at a current density of 10 mA cm 2, as anolyte to electrodeposit the polyelectrolyte on the membrane surface (catholyte was 0.0416N sodium chloride), a 1 1 mixed solution of 0.208N calcium chloride and 0.208 N sodium chloride was electrodialyzed at a current density of 10 mA cmr1 for 60 min (cation exchange membrane NEOSEPTA CH-45T).

Comparison of the diffusivities in Na,Ca-X and Na,Ca-A at comparable calcium exchange show [152] that the methane diffusivities are of the same order, while the n-hexane diffusivity in Na,Ca-A is much smaller than in Na,Ca-X. One has to conclude, therefore, that for the diffusion of the longer n-alkanes in Na,Ca-A it is justified to consider the passage through the windows as the rate-limiting step. For methane and ethane, however, the transport properties are dominated by the interaction with the cations. MD simulations of methane in Na,Ca-A are in satisfactory agreement with the NMR data and confirm this conclusion [154]. 

Another possibility deserving consideration is that some of the phytoestrogen effects may be attributable to properties that do not involve estrogen receptors, such as effects on enzymes, protein synthesis, cell proliferation, angiogenesis, calcium transport, Na /K adenosine triphosphatase, growth factor action, vascular smooth muscle cells, lipid oxidation, and cell differentiation. Some of these properties will be further discussed. 

Panfili, E., Sandri, G. Sottocasa, G.L. (1974) Some Properties of an Isolated Glycoprotein Possibly Related to Calcium Transport in Mitochondria , Acta Vitaminologia et Enzymologia, 28, 323-30... 

Among the enniatin antibiotics, beauvericin is the one characterized in greater detail. This carrier is most interesting with respect to an anion-dependence of its transport properties Moreover, in contrast to valinomycin, it is capable of com-plexing alkaline earth as well as alkali metal ions . A study of the effects of beauvericin on the conductivity of artificial lipid membranes in the presence of both mono- and divalent cations revealed a second-order relationship between conductance and antibiotic concentration Finally, Prince, Crofts, and Steinrauf detected an apparent charge of plus one for calcium in the beauvericin-mediated transport across bacterial chromatophore membranes... 

P. S. Thomas, P. A. Sreekumar, A. S. Aprem and S. Thomas, Poly(ethylene-co-vinyl acetate)/calcium phosphate nanocomposites Mechanical, gas permeability, and molecular transport properties. Journal of Applied Polymer Science, 2011, 120, 1974. 

Although most polypeptide hormones are unable to elicit energy-linked calcium movements in isolated mitochondrial preparations, some basic proteins share this property with parathormone. The doses of parathormone needed to affect mitochondria in vitro largely exceed the doses needed to modify kidney calcium transport in vivo. One could, however, argue that the in vitro conditions are not favorable for proper attachment of the hormone to the target, and therefore much more hormone is needed in vitro than in vivo. 

Calcium oxide CaO For general remarks, see the comments on the transport properties of MgO on p. 659. The transport of charge... 

Cd " and Mn may also be substrates for ion efflux mechanisms such as the Na-Ca exchanger (Frame and Milanick 1991). It has long been appreciated that a number of metals, and in particular and Mn ", inhibit this exchanger (Philipson 1985). Recent studies by Frame and Milanick (1991) demonstrate that this inhibition is competitive, and that these metals are in fact transported as substitutes for Ca. The for Ca, Cd ", and Mn uptake by ferret red blood cells is roughly similar, —10//M, as is the (Frame and Milanick 1991), indicating that the transport properties of cadmium and manganese are similar to those of calcium in this system. 

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