The occurrence of
fructose 2,6-bisphosphate was detected in Dictyostelium discoideum. The levels of this compound were compared with those of
cyclic AMP and several glycolytic intermediates during the early stages of development. Removal of the growth medium and resuspension of the organism in the differentiation medium decreased the content of
fructose 2,6-bisphosphate to about 20% within 1 h, remaining low when
starvation-induced development was followed for 8 h. The content of
cyclic AMP exhibited a transient increase that did not correlate with the change in
fructose 2,6-bisphosphate. If after 1 h of development 2%
glucose was added to the differentiation medium,
fructose 2,6-bisphosphate rapidly rose to similar levels to those found in the
vegetative state, while the increase in
cyclic AMP was prevented. The contents of
hexose 6-phosphates,
fructose 1,6-bisphosphate and triose
phosphates changed in a way that was parallel to that of
fructose 2,6-bisphosphate, and addition of
sugar resulted in a large increase in the levels of these metabolites. The content of
fructose 2,6-bisphosphate was not significantly modified by the addition of the 8-bromo or dibutyryl derivatives of
cyclic AMP to the differentiation medium. These results provide evidence that the changes in
fructose 2,6-bisphosphate levels in D. discoideum development are not related to a
cyclic-AMP-dependent mechanism but to the availability of substrate.
Fructose 2,6-bisphosphate was found to inhibit
fructose-1,6-bisphosphatase activity of this organism at nanomolar concentrations, while it does not affect the activity of
phosphofructokinase in the micromolar range. The possible physiological implications of these phenomena are discussed.