The Standard Potential of Glucose Oxidase

Glucose oxidase was titrated with Cr(II) and with Ti(III) over a pH range from 5.0 to 6.0, and a temperature range of 25° to 40°C. The two inorganic reagents were used, rather than just one, to ensure that there was no specific interaction between the enzyme and the reagent. Simultaneously, it was shown that the stoichiometry of the enzyme‐inorganic reductant reaction was identical to that of the enzyme‐glucose reaction and that the reduction products were identical in each case. Thus, it is shown that the potentials found are truly those which apply in the enzymatic oxidation of glucose. Glucose could not be used as reductant in the potentiometric studies because neither the enzyme nor the glucose reacts at the electrode. The values of (median reduction potential at pH 7) are −0.061v at 40°C, −0.028v at 30°C, and −0.008v at 25°C.