Resorufin as an electron acceptor in glucose oxidase-catalyzed oxidation of glucose

Resorufin (1) has been found to act as an electron acceptor in glucose oxid ase (GOD)-catalyzed oxidation of glucose. When a 1 : 1 : 1 mixture of solut ions of 1 (5.0 mu M), glucose, and GOD (4.0 mg/ml) in phosphate buffer (pH 7.4, 0.1 M) was incubated at 36 degrees C under aerobic conditions and the reaction was followed by a measurement of changes in fluorescence intensity due to 1, only two types of fluorometric traces were observed: (1) when a glucose solution of less than 0.7 mM was subjected to the enzymatic reactio n, no consumption of 1 was observed; (2) the reaction with glucose at more than 1.0 mM always consumed I, affording a regression fluorometric curve, a nd yet the obtained fluorometric traces could be almost superimposed on one another with no dependence on the glucose concentration. The reasons for t he observed phenomena are discussed.