FRUCTOSE 1,6-DIPHOSPHATASE OF DICTYOSTELIUM DISCOIDEUM

Fructose 1,6-diphosphatase from the slime mold Dictyostelium discoideum was found to have an alkaline pH optimum (9.0-9.5). Little or no activity occurred at physiological pH unless EDTA was added. In the presence of 0.2 mM EDTA an additional peak of activity, equal to that at pH 9.5, appeared at pH 7.5-8.0. EDTA stimulated activity at each pH tested (7.5, 8.5, and 9.5). Stimulation of activity was greatest at pH 7.5 and progressively decreased at high pH. The reaction was completely dependent upon the presence of Mg2+ or Mn2+. At optimum concentrations the reaction rate with Mg2+ was about three times higher than with Mn2+. In addition to EDTA, mercaptoethanol, cysteine, dithiothreitol, KCN, and histidine stimulated the reaction rate at pH 7.5. Adenosine monophosphate, deoxyadenosine monophosphate, 3′,5′-cyclic adenosine monosphosphate, adenosine diphosphate and adenosine triphosphate did not stimulate nor inhibit enzyme activity at pH 7.5 in the presence of 0.2 mM EDTA. Fructose 1,6-diphosphate was slightly inhibitory above 0.2 mM. The low activity of the enzyme as well as the lack of regulation of its activity by 3′,5′-cyclic adenosine monophosphate suggests that it may not be important in gluconeogenesis. © 1969, American Chemical Society. All rights reserved.