Oxygen absorption accompanying enzymic reaction. Oxidation of d-glucose in the presence of glucose oxidase and catalase.

Abstract

On absorption of pure oxygen gas through a free surface into d-glucose solution with low- and high-activity enzymes consisting of glucose oxidase and catalase or with these deactivated enzymes, the absorption rate NA and oxygen concentration in the bulk of liquid, Ao, were measured in a batch stirred tank (BST). Also, oxygen absorption rates for a solution consisting of d-glucose, active enzymes and sulfate were measured in the Warburg apparatus (WA). In the BST, the liquid-phase mass-transfer coefficient without chemical reaction, k*l, increases according to deactivated enzymes. For high content of low-activity enzymes, the observed values of NA and Ao are in good agreement with predicted values on the basis of chemical absorption theory. For high-activity enzymes, the rate equation of complex reaction is obtained from analysis of observed data. It was also clarified that the real value of enzyme activity in Sarett units, EUreal, is obtained from the Lineweaver-Burk (LB) plots of oxygen absorption rate per unit liquid volume per unit mass of enzyme, NA/(VlCEt), and Ao, where the overall rate is controlled by chemical reaction in the bulk of liquid. In the WA, the values of interfacial area al and k*lal were obtained from oxygen absorption into a solution consisting of d-glucose, sulfite and sulfate with and without cobaltous chloride catalyst at pH 8. For low- and high-activity enzymes, the respective reaction-rate constant and Michaelis constant given from analysis of observed values of NA agree well with those given in the BST. It was also proved that without observed values of Ao the EUreal for both enzymes are obtained from the LB plots of NA/(VlCEt), and (1-β*), where β* is the modified reaction coefficient. Thus, the EUreal for low- and high-activity enzymes coincide with those in the BST.