Polysaccharides calcium-binding

Several other properties of selected dietary fibers may influence the bioavailability of calcium directly or indirectly. Those fibers which have cation exchange capabilities such as acid polysaccharides due to free carboxyl groups on the sugar residues may bind minerals such as calcium (3,17,33,36). Loss of calcium binding protein as a result of mucosa injury caused by the feeding of some kinds of dietary fiber was credited as being the partial cause of decreased calcium absorption in everted, rat gut sac studies by Oku et al. (16). 

The carbohydrate components of hard-pieces of invertebrates have been reviewed recently416. Sulfated polysaccharides have been identified as Ca-binding sites of septal nacre from Nautilus pompilius430 This indicates that the site is a sulfated polysaccharide (s), and may be a sulfated, calcium-binding glycoprotein similar to the one isolated from Mercenaria mercenaria414 ... 

Smith, Q. T., Lindenbaum, A. Composition and calcium-binding of protein-polysaccharides of calf nasal septum and scapula. Calc. Tiss. Res. 7, 290 (1971)... 

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. 

Polysaccharides with calcium-binding sites may also serve to initiate deposition of calcium carbonate. 

Aeration, water-holding capacity, and permeability are all improved by humus. The frequent addition of easily decomposable organic residues leads to the synthesis of complex organics (e.g., polysaccharides) that bind soil particles into aggregates. The intimate association of clay-sized particles (layer silicates) with humus via cation (e.g., calcium, magnesium, aluminum, iron) bridges also promotes aggie-... 

Among the miscellaneous applications of ion-selective electrodes are the use of the Orion calcium electrode for studying calcium ion activity in connection with membrane alkalinisation in mitochondria [282] and on mitosis [283—285]. The electrode has also been used to show that protein polysaccharides of cartillage chelate calcium ions very effectively [286]. Electrode studies of calcium binding by chondroitin sulphate are said to be subject to interference by the condroitin sulphate anion [287]. 

The conformation of acidic polysaccharides and their interactions with calcium ions was examined by molecular simulation, and the authors demonstrated the existence of specific calcium binding with poly-a-L-guluronate [56, 57], The mechanism of complex formation involves calcium interactions with different oxygen atoms of two adjacent guluronic acid units and with two inter-chain units, as visualized in the egg-box model (Fig. 24.7). The mechanism of gelation is a two-step process first step is a dimer formation, followed by precipitation for small chains, or gelation for long ones formed with different types of blocks. 

The unit cell is trigonal, with a = b = 1.28 nm and c = 2.74 nm. Two chains, each with a 3(— 0.913) helix, pass through the unit cell. All three axes of the unit cell are shorter than those observed for the sodium salt formBS 69 (a = b = 1.45 nm, and c — 2.88 nm). This was attributed to the greater degree of binding of calcium ion to the polysaccharide chain, compared to that of the sodium ions. 

Calcium is coordinated between certain uronic acid-containing polysaccharides (VIII), which can explain the tight binding of calcium and other multivalent ions in polysaccharide stmctures, and also how bivalent ions can induce gel formation in acidic polysaccharides such as alginic acid solutions. 

CRP binds not only the polysaccharides present in many bacteria, ftmgi, and protozoal parasites but—in the presence of free calcium ions—phosphorylchofine phosphatidylcholines, such as lecithin and polyanions, such as nucleic acids. In the absence of calcium ions, CRP also binds polycations, such as histones. 

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