Glucose catalytic coefficients

The chemical properties of the crystalline enzyme obtained from beef kidney cortex, have been studied extensively (72, 88). Based upon a molecular weight of 37,000, and a specific activity of 26,500 units/mg, the catalytic coefficient for glucose is calculated to be 0.98 X 106 (72). Because of this high efficiency, the nature of the active site is of considerable interest. 

Numerous workers have examined the rate constants for the mutaro-tation of D-glucose in the presence of acetic acid and sodium acetate in an attempt to ascertain whether equation 9 or 10 applies. Although the two equations differ widely, it is not easy to distinguish experimentally between them. It is probable that the concerted mechanism is of no significance in the mutarotation of sugars in aqueous solution, with the possible exception of reactions catalyzed by the water molecule, as will be discussed later. In solvents of low dielectric constant, the formation of ionic intermediates becomes less favored, and the concerted mechanism may apply. Some of the methods that have been used for studying these reactiqns and for determining the catalytic coefficients will be considered next. 

To evaluate the catalytic coefficients for a specific reaction, the rate expression, equation 9, is set up for the known catalysts. Then, a series of measurements is made under such conditions that certain terms in the equation are negligible and the contribution of the catalyst under study becomes important. Under these conditions, the effect of the concentration of the catalyst on the rate constant may be determined. For example, to determine the catalytic coefficients for the mutarotation of D-glucose in an aqueous sodium acetate-acetic acid solution, the following equation is set up ... 

In these experiments, the contributions of the D-glucosate ion to the total rate-constant ranged from 18 to 41 %, depending on the concentration of the sugar. In a subsequent investigation,230 the study was extended, and catalytic coefficients and heats of activation were determined for catalysis of the mutarotation of D-glucose in water by each of three acids and four bases. 

The catalytic beads were mixed with 0.1 M Lactose-Tris-HCl buffer solution of (pH 4.8 with stirring, 250 rpm, at room temperature for 30 min. Samples were taken every 5 min to assess the glucose production using glucose kit. Beads activity is given by the angular coefficient of the linear plot of the glucose production as a function of time. 

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