Purification and properties of 3-ketosucrose-forming enzyme from the cells of Agrobacterium tumefaciens.

A 3-ketosucrose-forming enzyme was purified from a soluble fraction of a sonic extract prepared from the cells of Agrobacterium tumefaciens grown on a sucrose medium. With the purified enzyme, FAD was shown to be the prosthetic group and it was also proved that the enzyme is a dehydrogenase. D-Glucose and D-glucosides showed the highest affinity for the enzyme and were converted to their corresponding 3-keto sugars. From these findings, in this paper the name of D-glucoside 3-dehydrogenase was proposed as a trivial name for the 3-ketosucrose-forming enzyme. Other characteristic properties of D-glucoside 3-dehydrogenase were as follows: (a) the K, values for sucrose and D-glucose are 3.8 X 10M4 M, and 1.6 X 1O-4 M, respectively; (b) the optimum pH is 6.0 to 6.7; (c) the presence of Ca+f ions at 10e3 M inhibits the reaction almost completely; and (d) at acidic pH values, such as 5.2, Atabrine (lo-3 M) shows a striking acceleration effect. A close similarity of substrate specEcity between the receptor site of the sucrose transport system and that of Dglucoside 3-dehydrogenase in A. tumefaciens was observed. The differences between these functional sites in their relation to sucrose are discussed.