Hydrolysis of -maltose

Many enzymes are extremely specific. For example, the enzyme maltase catalyzes the hydrolysis of maltose ... 

Using bond energies, estimate AH for the hydrolysis of maltose to... 

An early report from Shukla et al.129 showed efficient hydrolysis and isomerization reactions of disaccharides, including cellobiose, maltose, and lactose, over zeolites type A, X, and Y. Abbadi et al.130 studied the hydrolysis of maltose, amylose, and starch over the zeolitic materials H-mordenite, H-beta, and mesoporous MCM-41. The effect of temperature and pressure, as well as that of the Si/Al ratio of H-mordenite and H-beta zeolites, on their catalytic activity was investigated for the... 

A. Abbadi, K. F. Gotlieb, and H. van Bekkum, Study on solid acid catalyzed hydrolysis of maltose and related polysaccharides, Starch, 50 (1998) 23-28. 

The enzyme was examined by Fischer following earlier studies by Bour-quelot (39) in France. Bourquelot (39) reported that he had made known in 1883 that an extract from a culture of A. niger hydrolyzed maltose. He now provided evidence that the solution also caused hydrolysis of trehalose. However, since this activity was lost on heating to 63 °C but that responsible for the hydrolysis of maltose was maintained up to 75 °C, he concluded that the fungus produced two different ferments —one a maltase, the other a trehalase. 

It appears that the overall mechanism for the hydrolysis of maltose by glucoamylase will soon be delineated. A brief summary of how this is being accomplished deserves comment. 

Hydrolysis of maltose forms two molecules of glucose. The Cl - O bond is cleaved in this process, and a mixture of glucose anomers forms. The mechanism for this hydrolysis is exactly the same as the mechanism for glycoside hydrolysis in Section 27.7B. 

Problem 27.30 Draw a stepwise mechanism for the acid-catalyzed hydrolysis of maltose to two molecules of glucose. 

The problem of the acid-catalyzed hydrolysis of the carbohydrate orthoesters was brought nearer to the final solution by Pacsu s experiments on the hydrolysis of maltose methyl 1,2-orthoacetate. Since two adjacent hydroxyl groups on the same side of the plane are necessary for the formation of orthoester derivatives, the maltose methyl orthoacetate must have an -configuration. Hydrolytic experiments with very dilute hydrochloric acid confirmed this. Two consecutive reactions took place at a pH of 4. In the first reaction, the original specific rotation, Co ]d - -103.7 in pure water, increased to -1-134.6° within two minutes. The latter figure corresponds to the specific rotation of a-maltose 2-acetate. The second reaction k = 0.0095) corresponded to the downward muta-rotation of a-maltose 2-acetate. When the hydrogen-ion concentration,... 

Figure 1.6. Relationship of a-glucosidase inhibitors to high energy intermediates in hydrolysis of maltose.

Rate Constants and Kinetic Parameters for the Hydrolysis of Maltose and... 

Additional evidence includes the fact that the initial rate of hydrolysis of the cyclodextrins is much lower than the rate of hydrolysis of the corresponding malto-oligosaccharides. Whereas the hydrolysis of maltose and other disaccharides follows normal, first-order kinetics, the rate constant for the hydrolysis of amylose increases with time, until it becomes the same as that of maltose, perhaps because of an increase in non-reducing ends brought about by slow, internal cleavages. There is a decrease in the hydrolysis rate-constant of cellodextrins with an increase in... 

Maltose is a disaccharide of glucose units joined oi-1,4. It differs from cellobiose, which is also a glucose disaccharide with units joined / -1,4. The enzyme, maltase, catalyzes hydrolysis of maltose to two molecules of D-glucose. 

The reaction rate for the hydrolysis of starch (Eq. 2.1 in Table 3) is a Michaelis-Menten type model, which considers competitive product inhibition of glucose and substrate inhibition of starch. The hydrolysis of maltose (Eq. 2.2 in Table 3) is represented by a Michaelis-Menten type model with competitive product inhibition. These equations were tested by Lopez et al. [3] for hydrolysis of chestnut puree by an alpha and glucoamylase mixture. As the enzyme STARGEN also contains amormts of alpha and glucoamylase, it was not surprising that they (Eqs. 2.1-2.2 in Table 3) fit the hydrolysis data better than non-inhibitory Michaelis-Menten kinetics. 

Fig. 3.10 Profile of reaction rate versus pH for the hydrolysis of maltose with glucoamylase...

The hydrolysis of maltose by glucoamylase from Rhizopus niveus was carried out in the presence an d absence of dextran sulphate, which are the components of supports of immobilized enzymes.The interaction between dextran and the enzyme was observed by fluorescence spectrophotometry. The kinetic and fluorescence experiments indicated that dextran became bound to glucoamylase and was apparently a non-competitive inhibitor of the enzyme. The dissociation constant of the enzyme-dextran complex was estimated to be 34%. The reaction rate was hardly affected at pH 4.0 and 4.5 by addition of dextran sulphate, whereas the kinetic parameters depended considerably on the concentration of dextran sulphate at pH 3.5. These findings indicated that there might exist some interactions between the enzyme and dextran sulphate. 

The hydrolysis of maltose by glucoamylase has been studied in the absence and presence of dextran and dextran sulphate. Dextran became bound to glucoamylase and was a non-competitive inhibitor of the enzyme. The reaction rate was hardly affected at pH 4.0-4.5 by dextran sulphate addition but depended considerably on dextran sulphate at pH 3.5, suggesting some kind of interaction between the two. The transport and metabolism of dextran [ S] sulphates of various molecular weights and sulphur contents in rat intestinal mucosa, and the effects of calcium thereon, have been investigated. Results suggested that dextran sulphates are transferred by pinocytosis and other mechanisms and are then desulphated mainly in microsomes, and subsequently become depolymerized. 

Reducing power of the reaction products at the hydrolysis of maltose, maltotriose, maltotetraose, maltopentaose and maltohexaose catalyzed by Aspergillus oryzae -amylase at Pjj 5.2 and 370C. Enzyme concentration 1.62x10 6 m. 

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