Carbohydrates calcium complexes with

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. 

Sesame seed has about 17% seed weight as hull, which is high in oxalic acid (2 3%), calcium, and cmde fiber. Oxalic acid could complex with calcium and reduce its bioavailabUity indigestible fiber would reduce the digestibihty of protein. Sesame seed hull is therefore recommended to be removed if sesame meal is used for human food (18). When sesame seed is properly dehulled, the oxalic acid content can be decreased to less than 0.25% of the seed weight (19). After dehulling, the fat and protein contents are raised, whereas the fiber, ash, and carbohydrate contents are lowered (Table 2). 

Because the two regioisomeric products 8a and 8b have almost the same molecular dimensions, it is difficult to discriminate between the two isomers with the geometric constraints imposed by the zeolite pores. Considering that calcium ions are apt to form mainly five-membered chelate complexes with polyhydroxy compounds (Fig. 4b) 32,33) and that calcium zeolites have also been employed as sorbents in carbohydrate separations (ii), it is possible to speculate that in the CaY-supported NaN3 system the epoxy alcohol first forms a coordinated structure around a calcium ion, as shown in Fig. 4a, followed by ring opening with an azide anion at the C-3 position of the epoxy alcohol, giving a stable, five-membered chelate complex with the calcium ion. 

Carbohydrates (and sugar alcohols) can form a complex with calcium and other metal ions if three of their OH groups form a series axial-equatorial-axial ... 

Table IV also includes some values determined in methanol as the solvent these are very much higher (and, hence, also more accurate) than those in water, because the polyol competes with methanol, rather than with water, for outer-sphere positions on the cation. These figures explain why carbohydrates are soluble in methanol or ethanol containing high concentrations of calcium chloride, or even potassium acetate, and in such systems as lithium chloride in 2-methoxyethanol. ° Sugar derivatives that are soluble in non-hydroxylic solvents form complexes with cations in those solvents even more readily for example, methyl 2,3-0-isopropylidene-4-0-methyl-) -L-rhamnopyranoside (24) (but not its a anomer) will form a complex with sodium iodide in acetone, the Na" " ion coordinating to 0-1,0-2, and 0-3. In aqueous solution, the concentration of this complex would be negligible.

Electrolytes which do not afford ionic complexes with common hexitols and reducing sugars are aqueous solutions of lead acetate, copper sulfate, zinc sulfate, ferrous ammonium sulfate, calcium chloride, potassium dichromate, ferric chloride (pH 3), aluminum sulfate, magnesium sulfate, sodium sulfate, potassium antimonyl tartrate, sodium arsenate or arsenic acid, sodium phosphate, and hydrochloric acid. It is not certain whether sodium aluminate (in 0.1 N sodium hydroxide) affords ionic complexes with carbohydrates, as aqueous alkali, alone, permits their migration during electrophoresis. 

The cellular tissue of many fruits contains cellulose associated with other substances of the nature of carbohydrates. Apples, pears, and other fruits contain a substance called pecto-cellulose, which is probably a chemical compound of cellulose and pectin, as it gives cellulose and pectic acid on hydrolysis with an alkali. Pectin, which is a complex carbohydrate present in certain fruits, is converted into pectic acid when heated with a solution of an alkali. The formation of jellies from fruits is brought about as the result of the hydrolysis of the pectin which they contain. The hydrolysis converts pectin into pectic acid, which forms calcium pectate with the calcium salts always... 

In the field of wine analysis within the European Union, the analytical methods are defined to a large extent by VO (EWG) No. 2676/90 [216]. Therefore, wet-chemical and enzymatic techniques still play an important role. However, the hquid chromatographic determination of the main sugars such as glucose, fructose, and sucrose together with glycerol and ethanol gains in importance due to its potential for automation. Separation is performed on a calcium-loaded ion-exclusion phase with pure de-ionized water as an eluant refrachve index detection is applied [217]. Thus, carbohydrate separation is based on the formation of different coordination complexes with metal cations, whose stability de-... 

One of the first historical confirmations of the structure of the carbohydrate complex with metals was the X-ray study of the crystal stracture of sucrose NaBr 2H2O. It has to be merrtioned that sucrose does not form the corrrplex in the solution [24], In 1972 crystal stracture of sugar arrd calcium was determined for D-man-nose CaClj 2H2O. Calcium in this case is coordirrated to Ol, 02, and 03 of one P-furanose ring arrd to 05 and 06 of the another rrtarmose molecule [25],... 

Figure 4. Modelled structure of a trimeric fragment of rat serum MBP in complex with carbohydrate ligands. The model has been created using the coordinates from the crystal structure of a trimeric fragment of rat serum MBP comprising part of the neck region and CRDs and the structure of the isolated CRD in complex with a mannose-containing oligosaccharide. Calcium ions are shown in grey. A third Ca " thought to be an artifact of the crystallization conditions is shown in white. Reproduced from [331.

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