Glucose complex formation

As a final example we consider noncovalent molecular complex formation with the macrocyclic ligand a-cyclodextrin, a natural product consisting of six a-D-glucose units linked 1-4 to form a torus whose cavity is capable of including molecules the size of an aromatic ring. Table 4-3 gives some rate constants for this reaction, where L represents the cyclodextrin and S is the substrate ... 

However, there are a number of other miscellaneous biological roles played by this complex. The [Co(NH3)6]3+ ion has been shown to inhibit the hammerhead ribozyme by displacing a Mn2+ ion from the active site.576 However, [Co(NH3)6]3+ does not inhibit ribonuclease H (RNase),577 topoisomerase I,578 or hairpin ribozyme,579 which require activation by Mg2+ ions. The conclusions from these studies were that an outer sphere complex formation between the enzyme and Mgaq2+ is occuring rather than specific coordination of the divalent ion to the protein. These results are in contrast to DNase I inhibition by the same hexaammine complex. Inhibition of glucose-induced insulin secretion from pancreatic cells by [Co(NH3)6]3+ has been found.580 Intracellular injection of [Co(NH3)6]3+ into a neurone has been found to cause characteristic changes to the structure of its mitochondria, and this offers a simple technique to label neuronal profiles for examination of their ultrastructures.581... 

Addition of an aqueous solution of PEG to a saturated aqueous solution of a-CD at room temperature did not lead to complex formation unless the average molecular weight of PEG exceeded 200 [46]. Moreover, carbohydrate polymers such as dextran and pullulan failed to precipitate complexes with PEG, and the same was true for amylose, glucose, methyl glucose, maltose, maltotriose, cyclodextrin derivatives, such as glucosyl-a-CD and maltosyl-a-CD, and water-soluble polymers of a-CD crosslinked by epichlorohydrin. These facts suggested to Harada et al. the direction for further research. 

Kitano S, Kataoka K, Koyama Y et al (1991) Glucose-responsive complex formation between poly (vinyl alcohol) and poly(lV-vinyl-2-pyrrolidone) with pendent phenylboronic acid moieties. Makromol Chem Rapid Commun 12 227-233... 

To neutralize the hydrolysis products the solution is passed through a column (of about 15-cm length and 1-cm width) packed with an anion exchanger (e.g.,anion exchanger from Example 5-10). Neutralization with alkaline earth metal carbonates is to be avoided at all costs, in order to prevent epimerization of glucose to mannose which is favored by complex formation between mannose and alkaline earth metal ions. 

IL-1 also appears to inhibit insulin secretion by modulating the mitochondrial oxidative metabolism of purified P cells. Treatment of purified P cells for 18 hr with IL-1 results in nearly complete inhibition of the oxidation of [ CJ-D-glucose to C02 (Fig. 10). This inhibition is completely prevented by NMMA (Corbett et al., 1992b). Treatment of purified a cells with lL-1 has no effect on glucose oxidation, suggesting that the effects of IL-1 are specific to the endocrine P cell (Fig. 10). These findings are further supported by the observation that lL-1 induces iron-nitrosyl complex formation and the accumulation of cGMP in the... 

Lea, C. H. and Hannan, R. S. 1950. Studies of the reaction between proteins and reducing sugars in the dry state. II. Further observations on the formation of the casein-glucose complex. Biochem. Biophys. Acta 4, 518-531. 

With the establishment of the permease hypothesis, however, it was apparent that the mere formation of a complex with the mutarotase protein may be the necessary interaction in transport (15). The subsequent mutarotation could be considered to be a coincidental consequence of the complex formation. To support this idea, it was found that 1-deoxy glucose and a-methyl glucoside are excellent competitive inhibitors of the enzyme (16,61). Keston also showed that a number of cataractogenic sugars were inhibitors of lens mutarotase (62). It has since been shown that in all cases where a sugar is a substrate for the mammalian intestinal transport system it is also a competitive inhibitor of mutarotase. 

The key function of sodium is its role in assisting the absorption of glucose and water from the small intestine, both by complex formation (Schultz and Crnran, 1970) and by a phenomenon known as solution drag (Fordtran, 1975). Sodium also aids post-activity recovery by ... 

The Mn(II)-catalysed oxidation of glucose by peroxodisulfate ions occurs via a radical-chain mechanism.26 Kinetics of oxidation of thiodiglycollic acid by (trans-cyclohexane-l,2-diaminc-/V, N, N, /V -tetraacetatolmanganateilJI) have been investigated.27 Oxidations of ketoses and aldoses by manganese(IV) in sulfuric acid media have a first-order dependence on sugar and fractional-order dependence on oxidant.28 A mechanism has been proposed for the oxidation of L-malic acid by Mn(III) pyrophosphate in aqueous acid, involving complex formation and radicals.29... 

In the cyclodextrins readily obtainable from starch, the six (a-CD), seven (P-CD) and eight (y-CD) a(l- 4)-linked glucose units are "locked up" in a strait-jacket type belt due to adoption of 4Cj chair conformations of the pyranoid rings and a net of 2-OH — OH-3 hydrogen bonds (73, 74). As this structural rigidity even persists on inclusion complex formation, as exemplified by the three represenatives in Fig. 1 (75 - 78) ... 

Recent experiments in our laboratory have shown that a thermal gradient is not necessary for complex formation with potato starch. In the presence of suitable compounds, the gelatinized potato starch forms helices under complex formation at isothermal conditions. The reaction takes place even at low concentrations of ligand compounds under conditions occuring in any food system containing potato starch. The reaction can easily be followed by amperome-tric titration with jodine (24). The complexes formed can be analyzed by using a combination of glucose determination and G.C. analysis. 

Figure 2. Isotherms of complex formation of potato starch with decanal—starch (as glucose) 0.613 mM decanal variable H20 10 mL pH 7.0 temperature ...

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