Calcium carbohydrate interaction

The complexation of M"+ by carbohydrates is now well known.342 The conditions that influence such complexation have been discussed at length, as have complexation processes in solution with particular reference to NMR studies.243 Structural aspects of calcium-carbohydrate interactions have also been reviewed.244... 

Dheu-Andries ML, Perez S (1983) Geometrical features of calcium-carbohydrate interactions. Carbohydr Res 124(2) 324-332. doi 10.1016/0008-6215(83)88468-7 Beevers CA, Cochran W (1947) The crystal structure of sucrose sodium bromide dihydrate. Proc R Soc London Ser A 190 257-272. 

Carbohydrates not only interact with protein receptors, but also with other carbohydrates and nucleic acids. Recently, gold nanoparticles (GNPs) have been prepared as new multivalent tools that mimic carbohydrate presentation on the cell surface. Using this tool, a weak calcium-mediated carbohydrate-carbohydrate interaction has been detected using NMR, employing... 

Dch < 10 Hz), where the interference of proton—proton RDCs and the variations in the one-bond splitting is minimal. These highly accurate methods were recently used to measure 1 >ch RDCs as a function of the carbohydrate concentration. The observed changes provided evidence for the existence of calcium-mediated interactions between Lewis X-related trisaccharides.184... 

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. 

To understand the inhibition of a-amylase by peptide inhibitors it is crucial to first understand the native substrate-enzyme interaction. The active site and the reaction mechanism of a-amylases have been identified from several X-ray structures of human and pig pancreatic amylases in complex with carbohydrate-based inhibitors. The structural aspects of proteinaceous a-amylase inhibition have been reviewed by Payan. The sequence, architecture, and structure of a-amylases from mammals and insects are fairly homologous and mechanistic insights from mammalian enzymes can be used to elucidate inhibitor function with respect to insect enzymes. The architecture of a-amylases comprises three domains. Domain A contains the residues responsible for catalytic activity. It complexes a calcium ion, which is essential to maintain the active structure of the enzyme and the presence of a chloride ion close to the active site is required for activation. 

Complexes of alkali metals and alkaline-earth metals with carbohydrates have been reviewed in this Series,134 and the interaction of alkaline-earth metals with maltose has been described.135 Standard procedures for the preparation of adducts of D-glucose and maltose with the hydroxides of barium, calcium, and strontium have been established. The medium most suitable for the preparation of the adduct was found to be 80% methanol. It is of interest that the composition of the adducts, from D-glucose, maltose, sucrose, and a,a-trehalose was the same, namely, 1 1, in all cases. The value of such complex-forming reactions in the recovery of metals from industrial wastes has been recognized. Metal hydroxide-sugar complexes may also play an important biological role in the transport of metal hydroxides across cell membranes. 

Figure 11.29. Structure of a C-Type Carbohydrate-Bindiug Domain from an Animal Lectin. A calcium ion links a mannose residue to the lectin. Selected interactions are shown, with some hydrogen atoms omitted for clarity.

Reeves (1997) has discussed the current recommendations of the American Institute of Nutrition (AIN) for assembling rat diets. Issues discussed include the use of sugar versus starch as the source of carbohydrate, methionine versus cystine as the source of cysteine, and the best oil for providing the essential fatty acids. In embarking on any study, the researcher needs to reevaluate the role of each of the recommended nutrients to make sure that their quantities suit the purposes of the planned experiment. For example, although the AIN recommends using casein as the source of protein, researchers interested in the interactions of calcium and phosphate need to take into accoimt the fact that casein contains significant amounts of phosphate. 

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