Calcium ions, interactions with

Calcium ion interactions with calmodulin, THERMODYNAMIC CYCLES Calcium oxalate,... 

The three commonly observed modes of calcium carboxylate ligation. (A) The unidentate mode, in which the calcium ion interacts with only one of the two carboxylate oxygens. (B) The bidentate mode, in which the calcium ion is chelated by both oxygen atoms. (C) The a-mode, in which the calcium ion is chelated by one carboxylate oxygen, and another ligand is attached to the a-carbon. Adapted from Reference 11. 

Here we report the effect of calcium ion binding to carboxylates that exhibit hydrophobic-induced pKa shifts. The pKa shifts result from the work required to destructure hydrophobic hydration in the process of ionization to form the carboxylate. In Figure 5.27, calcium ion interaction with carboxylates makes two different model proteins more hydrophobic to different extents, depending on their initial oil-like composition. Figure 5.27A... 

Calcium ions interact with sulfonic acids more strongly than univalent cations. For instance, the ion-exchange constants in the monolayer of dodecylsulfate are equal to 300, 90, and 60 for the pairs Ca /Li , Ca /Na, Ca /Cs [109]. 

Galli mentioned the addition of alkali-earth metals (mainly calcium) to the BGE to improve separation of organic acids. Calcium ions interact through the formation of complexes with different stabilities giving different mobilities. EDTA may also be used to form different complexes. Alternatively, EDTA may remove interfering compounds. 

The resultant modified E residues are gamma-carboxyglutamate (gla). This process is most clearly understood for factor II, also called preprothrombin. Prothrombin is modified pre-prothrombin. The gla residues are effective calcium ion chelators. Upon chelation of calcium, prothrombin interacts with phospholipids in membranes and is proteolysed to thrombin through the action of activated factor X (Xa). Dining the carboxylation reaction reduced hydroquinone form of vitamin K is converted to a 2,3-epoxide form. The regeneration of the hydroquinone form requires an uncharacterized reductase. This latter reaction is the site of action of the dicumarol-based anticoagulants such as warfarin. 

Calcium carbonate interacts with hydrooxonium ions to form carbonic acid and a calcium ion, with carbonic acid yielding CO2 and water ... 

Not fully understood. The cardiac glycosides inhibit sodium-potassium ATP-ase, which is concerned with the transport of sodium and potassium ions across the membranes of the myocardial cells. This is associated with an increase in the availability of calcium ions concerned with the contraction of the cells. Potassium loss caused by these diuretics exacerbates the potassium loss from the myocardial cells, thereby increasing the activity and the toxicity of the digitalis. Some loss of magnesium may also have a part to play. The mechanism of this interaction is still being debated. 

Non-covalent interactions between carbohydrate chains can be very powerful, as in the hydrogen-bonded structures of cellulose and chitin, and this is especially true if the bonds have a polar character and are in a hydro-phobic environment. Likewise, saccharide chains may interact through coordination of metal ions for example, the hydroxyl group—calcium ion interaction can be strong if steric factors favour it. Carbohydrates may also interfere dramatically with the structure of water, but all of these fascinating possibilities do not carry clear biosynthetic implications and so must lie largely outside the scope of this chapter. 

D.W. Urry, N. Jing, T.L. TVapane, C-L. Luan, and M. Waller, (1988a) Ion interactions with the gramicidin A transmembrane channel cesium-133 and calcium-43 NMR studies. In W. Agnew, T. Claudio, and F. Sigworth (eds) Mol Biol of Ionic Channels 33, (vol. pp. 51-90) Academic Press, Inc., New York. 

Low methoxylated (esterified) pectins can form gels in the presence of divalent cations, usually calcium. The interaction with calcium ions of fragments of two D-galacturonic acid adjacent units... 

Traditionally remineralization of tooth structures have relied on well established concepts of nucleation and crystal growth. Mineral ions interact with the tooth substrate and crystallization occurs at specific thermodyuamic conditions that are appropriate for formation of an stable apatite phase in register with the preserved tooth structures. Using these approaches, researchers have been able to demonstrate that in carious dentin, the intrafibrillar mineral that is not fully dissolved upon acidic attack may function as nucleation sites for subsequent deposition of calcium and phosphate within the intrafibrillar compartments of collagen fibrils [127]. This, in turn, has been shown to lead to significant increases in the mechanical properties of partially demineralized dentin. 

Melittins are peptides of 26 amino acids found in Apis venoms (119, 120). Melittin comprises about 40% to 50% of the dry weight of Apis mellifera venom. At moderate and high concentrations, it exists primarily in the form of tetramers (120, 121), which can be immunogenic and allergenic (123). Tetrameric melittin is a potent lytic agent for cells and can also function as an ion channel (124, 125, 126). Melittin has profound effects on intracellular calcium and interacts with calmodulin (127, 128, 129). It is an amphiphilic and amphipathic molecule that has been found to be very useful in studies of cell lysis, membrane function, calcium regulation and as a model for proteins and peptides. Natural and synthetic melittin have been used in over a 1000 published studies in many areas of science. 

Most potentiometric electrodes are selective for only the free, uncomplexed analyte and do not respond to complexed forms of the analyte. Solution conditions, therefore, must be carefully controlled if the purpose of the analysis is to determine the analyte s total concentration. On the other hand, this selectivity provides a significant advantage over other quantitative methods of analysis when it is necessary to determine the concentration of free ions. For example, calcium is present in urine both as free Ca + ions and as protein-bound Ca + ions. If a urine sample is analyzed by atomic absorption spectroscopy, the signal is proportional to the total concentration of Ca +, since both free and bound calcium are atomized. Analysis with a Ca + ISE, however, gives a signal that is a function of only free Ca + ions since the protein-bound ions cannot interact with the electrode s membrane. 

Other Reactions of Phospholipids. The unsaturated fatty acid groups in soybean lecithin can be halogenated. Acetic anhydride combined with the amino group of phosphatidylethanolamine forms acetylated compounds. PhosphoHpids form addition compounds with salts of heavy metals. Phosphatidylethanolamine and phosphatidjhnositol have affinities for calcium and magnesium ions that are related to interaction with their polar groups. 

Extrinsic Pathway. Coagulation is initiated when tissue extracts with Hpid—protein properties are released from the membranes of endothehal cells following injury or insult. These substances, collectively designated tissue thromboplastin, complex with circulating Factor VII and in the presence of calcium ions subsequentiy activate Factor X (Fig. 1). In vitro evidence suggests that Factor X can be activated less rapidly through the interaction of kaUikrein [9001-01-8] with Factor VII. 

Components in the invading water-based filtrate and in the formation waters may react to form insoluble precipitates which can block the pores and give rise to skin damage. The scale can be formed by interaction of calcium-based brines with carbon dioxide or sulfate ions in the formation water. Alternatively sulfate ions in the invading fluid may react with calcium or barium ions in the formation water. Analysis of the formation water can identify whether such a problem may arise. 

The action of a peptidase can be neutralized by an inhibitor. Some inhibitors are very broad in their action and are capable of inhibiting many different peptidases, including peptidases of different catalytic types. Some inhibitors are assumed to be specific for a particular catalytic type, but can inhibit peptidases of different types. Leupeptin, for example, is widely used as an inhibitor of serine peptidases from family SI, but it is also known to inhibit cysteine peptidases from family Cl. Cysteine pqrtidase inhibitors such as iodoacetic acid interact with the thiol of the catalytic cysteine. However, this reduction can occur on any thiol group and can affect other, predominantly intracellular, peptidases with a thiol dependency. One example is thimet oligopepti-dase. Metal chelators such as EDTA can inhibit meta-llopeptidases, but can also affect peptidases that have a requirement for metal ions that is indq>endent of their catalytic activity, such as the calcium-dependent cysteine endopqrtidase calpain 1. 

---