Calcium complexes proteins

The influx of Ca(Il) across the presynaptic membrane is essential for nerve signal transmission involving excitation by acetylcholine (26). Calcium is important in transducing regulatory signals across many membranes and is an important secondary messenger hormone. The increase in intracellular Ca(Il) levels can result from either active transport of Ca(Il) across the membrane via an import channel or by release of Ca(Il) from reticulum stores within the cell. More than 30 different proteins have been linked to regulation by the calcium complex with calmoduhn (27,28). 

Phosphates, which react with calcium to reduce the calcium ion activity, assist in stabilizing calcium-sensitive proteins, eg caseinate and soy proteinate, during processing. Phosphates also react with milk proteins. The extent of the reaction depends upon chain length. Casein precipitates upon addition of pyrophosphates, whereas whey proteins do not. Longer-chain polyphosphates cause the precipitation of both casein and whey proteins. These reactions are complex and not fully understood. Functions of phosphates in different types of dairy substitutes are summarized in Table 9 (see also Food additives). 

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

In striated muscle, there are two other proteins that are minor in terms of their mass but important in terms of their function. Tropomyosin is a fibrous molecule that consists of two chains, alpha and beta, that attach to F-actin in the groove between its filaments (Figure 49-3). Tropomyosin is present in all muscular and muscle-fike structures. The troponin complex is unique to striated muscle and consists of three polypeptides. Troponin T (TpT) binds to tropomyosin as well as to the other two troponin components. Troponin I (Tpl) inhibits the F-actin-myosin interaction and also binds to the other components of troponin. Troponin C (TpC) is a calcium-binding polypeptide that is structurally and functionally analogous to calmodulin, an important calcium-binding protein widely distributed in nature. Four molecules of calcium ion are bound per molecule of troponin C or calmodulin, and both molecules have a molecular mass of 17 kDa. 

It should be pointed out that the addition of substances, which could improve the biocompatibility of sol-gel processing and the functional characteristics of the silica matrix, is practiced rather widely. Polyethylene glycol) is one of such additives [110— 113]. Enzyme stabilization was favored by formation of polyelectrolyte complexes with polymers. For example, an increase in the lactate oxidase and glycolate oxidase activity and lifetime took place when they were combined with poly(N-vinylimida-zole) and poly(ethyleneimine), respectively, prior to their immobilization [87,114]. To improve the functional efficiency of entrapped horseradish peroxidase, a graft copolymer of polyvinylimidazole and polyvinylpyridine was added [115,116]. As shown in Refs. [117,118], the denaturation of calcium-binding proteins, cod III parvalbumin and oncomodulin, in the course of sol-gel processing could be decreased by complexation with calcium cations. 

It has been shown that the activity of NO synthases is regulated by cofactors calcium binding protein calmodulin and tetrahydrobiopterin (H4B). Abu-Soud et al. [149] have studied the effect of H4B on the activity of neuronal nNOS I, using the isolated heme-containing oxygenase domain nNOSoxy. It was found that nNOSoxy rapidly formed an oxygenated complex in the reaction with dioxygen, which dissociated to produce superoxide (Reaction (6)) ... 

Takeshima H, Komazaki S, Nishi M, lino M, Kangawa K 2000 Junctophilins A novel family of junctional membrane complex proteins. Mol Cell 6 11-22 van Breemen C, Farinas BR, Gerba P, McNaughton ED 1972 Excitation-contraction coupling in rabbit aorta studied by the lanthanum method for measuring cellular calcium influx. Circ Res 30 44-54... 

During the last decade, a number of investigators have attempted to elucidate the mechanism by which protein consumption induces hypercalciuria. In our previous research, the calciuria could not be explained by increased intestinal absorption of calcium, complexing with sulfur amino acids, or urinary acid production. 

A similar approach for detecting the presence of specific proteins has also been reported by Nilsson and coworkers [26]. In this study, a complex between a calmodulin, a small calcium-binding protein, and the zwitter-ionic polythiophene POWT was used to detect the presence of calcineurin. The interaction between the POWT-camodulin complex and calcineurin changed the emission profile from POWT, and no observable changes were observed upon exposure of the complex human serum albumin, suggesting that the complex could be used for the specific detection of calcineurin. 

The calcium mediated contraction of smooth muscle, which unlike striated muscle does not contain troponin, is quite different and requires a particular calcium-binding protein called calmodulin. Calmodulin (CM) is a widely distributed regulatory protein able to bind, with high affinity, four Ca2+ per protein molecule. The calcium—calmodulin (CaCM) complex associates with, and activates, regulatory proteins, usually enzymes, in many different cell types in smooth muscle the target regulatory proteins are caldesmon (CDM) and the enzyme myosin light chain kinase (MLCK). As described below, CaCM impacts on both actin and myosin filaments. 

Ion channels are large proteins which form pores through the neuronal membrane. The precise structure and function of the ion channels depend on their physiological function and distribution along the dendrites and cell body. These include specialized neurotransmitter-sensitive receptor channels. In addition, some ion channels are activated by specific metal ions such as sodium or calcium. The structure of the voltage-dependent sodium channel has been shown to consist of a complex protein with both a hydrophilic and a hydrophobic domain, the former domain occurring within the neuronal membrane while the latter domain occurs both inside and outside the neuronal membrane. 

Effect of vitamin D on the intestine 1,25-diOH D3 stimulates intestinal absorption of calcium and phosphate. 1,25-diOH D3 enters the intestinal cell and binds to a cytosolic receptor. The 1,25-diOH D3-receptor complex then moves to the nucleus where it selectively interacts with the cellular DNA. As a result, calcium uptake is enhanced by an increased synthesis of a specific calcium-binding protein. Thus, the mechanism of action of 1,25-diOH D3 is typical of steroid hormones (see p. 238). 

Stability of the complex protein system of milk or whey is decreased by concentration (Fox 1982 Muir and Sweetsur 1978 Sweetsur and Muir 1980B). In addition to closer packing of casein micelles and other proteins in concentrated milk, calcium phosphate is precipitated so that the pH decreases (Fox 1982). The pH effect causes protein which would be soluble at a normal solids concentration to precipitate. Casein in milk concentrated to three times its original solids level forms a flocculent after 1 to 3 weeks at -8°C (Lonergan 1978). 

The controlled deposition of calcium salts is essential for the development of extracellular structures such as bones, teeth and shell. The process begins with uptake of calcium in the intestine, followed by transport, and then the laying down of structures. A complex system is necessary for the control of all these stages, and involves, for example, vitamin D, parathyroid hormone, calcium-binding proteins for transport, and a range of other proteins and polysaccharides for ordered deposition. Precipitation of calcium salts in the incorrect location can result in stone formation, osteoarthritis, cataracts and arterial disorders. 

CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, C. Allen Bush. Raman Spectroscopy of Nucleic Acids and Their Complexes. George J. Thomas, Jr. and Masamichi Tsuboi. Oligosaccharide Conformation in Pro-tein/Carbohydrate Complexes, Anne Imberty, Yves Bourne, Christian Cambillau and Serge Perez. Geometric Requirements of Proton Transfers, Steve Scheiner. Structural Dynamics of Calcium-Binding Proteins, Robert F. Steiner. Determination of the Chemical Structure of Complex Polysaccharides, C. Abeygunawardana and C. Allen Bush. Index. 

Eue I, Sorg C. 2001. Arachidonic acid specifically regulates binding of S100A8/9, a heterodimer complex of the S100 class of calcium binding proteins, to human microvascular endothelial cells. Atherosclerosis 154(2) 505—508. 

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