GLUCOKINASE OF DICTYOSTELIUM DISCOIDEUM

Glucokinase from the slime mold Dictyostelium discoideum was purified 50-fold by DEAE-cellulose chromatography. The enzyme had a pH optimum of about 7.5. Mannose, fructose, and 2-deoxyglucose did not act as substrates or inhibitors of the enzyme. Only adenosine triphosphate served as the phosphate donor. No phosphorylation of glucose was observed with uridine triphosphate, cytidine triphosphate, inosine triphosphate, or guanosine triphosphate. The Km for glucose was 1.2 × 10-4 M and the Km for adenosine triphosphate was 1.1 × 10-3 M. Variations in the concentration of either substrate did not affect the Km of the corresponding substrate. Glucose 6-phosphate was a competitive inhibitor with respect to glucose and a noncompetitive inhibitor with respect to adenosine triphosphate. Adenosine diphosphate gave a mixed inhibition with respect to glucose and a noncompetitive inhibition with respect to adenosine triphosphate. No significant reduction of enzyme activity was observed with guanosine diphosphate, inosine diphosphate, cytosine diphosphate, uridine diphosphate, adenosine monophosphate, deoxyadenosine monophosphate, 3′,5′-adenosine monophosphate, inorganic phosphate, or pyrophosphate. Inorganic phosphate did not alter the inhibition by glucose 6-phosphate and adenosine diphosphate. The possible significance of the glucokinase reaction in D. discoideum metabolism is discussed. © 1969, American Chemical Society. All rights reserved.