Oxidation of Uronic Acids by a Large Excess of Glucose Oxidase Preparations

Three commercial enzyme preparations of glucose oxidase (GOD) showed an oxidizing ability of glucuronic acid and galacturonic acid to form sugar acids. The optimum conditions of GOD reaction were at pH 8.0 and 50°C, whereass those of uronic acid oxidase (UOD) reaction were at pH 3.5 and 40°C. In spite of extensive attempts to separate GOD from UOD, the isolation of each activity was unsuccessful, and UOD reaction resulted from the wide substrate specificity of GOD reaction. More than 6-fold higher Km values for glucuronic acid and galacturonic acid than for glucose might suggest that UOD reaction was the alternative reaction of GOD enzyme. However, a more definite conclusion on UOD activity should be drawn from further studies. The reaction products from uronic acids were analyzed by HPLC and paper chromatography, and some products were shown to be identical with sugar acids.