Sodium-calcium cation binding

Proteins bind these four cations with strengths that depend on the size of the cation and its charge. The higher the charge, the better the cation binds the binding of potassium and sodium ions is poorer than that of magnesium and calcium ions. The size is also important and a protein often provides a pocket of the correct size so that it can distinguish between... 

The anti-HSV-1 activity of Ca-SP was assessed by plaque yield reduction and compared with those of dextran sulphate as a representative sulphated PS. These data indicate that Ca-SP is a potent antiviral agent against HSV-1, as even at low concentrations of Ca-SP, no enhancement of virus-induced syncytium formation was observed, as occurred in dextran sulphate-treated cultures. Reeently, Lee et al. [73] investigated the effects of structural modifications of Ca-SP on antiviral activity. Calcium ion binding with the anionic part of the molecule was replaeed with various metal cations, and their inhibitory effects on the replication of HSV-1 were evaluated. Replacement of calcium ion with sodium and potassium ions maintained the antiviral activity, while divalent and trivalent metal cations reduced the activity. Depolymerization of sodium spirulan with hydrogen peroxide decreased the antiviral activity as its molecular weight decreased. 

The organic molecules in cells are mainly anionic. Sodium, as Na, cannot be allowed to neutralize these negative charges of the non-metal compounds inside cells because its external concentration (in the sea) is too high (10 m) and its entry would result in too great a cellular osmotic pressure. For this reason, Cl" also had to be largely rejected. Instead, potassium, K+, is selected for the uptake into the cytoplasm. Neither of these cations binds to organic molecules. Calcium, as Ca +, is also deleterious inside cells because at its environmental concentration (10 m) it... 

For example, Barlow and Margoliash [33] showed that phosphate, chloride, iodide, and sulfate, in decreasing order of effect, reduced the electrophoretic mobihty of human cytochrome c at pH 6.0 by up to a factor of 2. The cations lithium, sodium, potassium, and calcium had no effect. It is possible to account for the binding equilibria of these counterions so that the titration and electrophoresis results can be compared however, in many of the early electrophoresis experiments these data were not available and relevant conditions were not recorded or controlled. For general discussions on the extensive field of ligand binding to proteins, see Cantor and Schimmel [60] and van Holde [403]. 

Since the proteins contain negatively charged groups such as phosphates, side-chain carboxyls, terminal carboxyls, and sulfhydryls, they bind a number of different cations, such as calcium, barium, strontium, magnesium (Dickson and Perkins 1969), copper (Dill and Simmons 1970 Aulakh and Stine 1971), thallium (Sundararajan and Whitney 1969), potassium and sodium (Ho and Waugh 1965), iron (Basch et al. 1974, Demott and Park 1974 Demott and Dincer 1976), cadmium (Roh et al. 1976), and mercury (Roh et al. 1975). 

Metarhodopsin 11 activates transducin, leading to an exchange of bound GDP for GTP several hundred molecules of transducin are activated by a single molecule of metarhodopsin 11 within a fraction of a second. Transducin-GTP binds to, and activates, GMP phosphodiesterase, lowering the intracellular concentration of cGMP. As cGMP falls, a cation channel in the membrane closes, thus interrupting the steady inward current of sodium and calcium ions. This leads to hyperpolarization of the membrane and reduced secretion of neurotransmitter (Baylor, 1996). 

French town (Montmorillon) where it was first discovered. In the USA, bentonite is principally mined in Wyoming - hence the term Wyoming clay . The type of bentonite, the source, and its purity influence its properties (Marchal et al. 1995). Bentonite is a complex hydrated aluminum silicate with exchangeable cationic components (Al, Fe, Mg) Si40io (0H)2 (Na+, Ca++). The most commonly used bentonite form in enology is the sodium bentonite. Sodium bentonite has enhanced protein binding capabilities over calcium bentonite. 

Magnesium is the fourth most abundant cation in the body after sodium, potassium, and calcium, and is the second most abundant cation in intracellular fluid after K+ Mg + is needed in many enzymatic reactions, particularly those in which ATP Mg + is a substrate. Magnesium binds to other nucleotide phosphates and to nucleic acids and is required for DNA replication, transcription, and translation. The DNA helix is stabilized by binding... 

Repair of the calcium gate/block due to diffusion occurs equally simply because of ionic depletion and competitive association. In particular, relaxation of the sodium or potassium ionic gradient in the vicinity of the open channel mouth quickly brings the levels of these ions locally to that of calcium. At that point, calcium competes effectively to bind to the phosphate. The system repairs to its resting state. The monovalent cations then can build up the concentration gradients observed through diffusion. 

---