Stimulation of Trypanosoma brucei pyruvate kinase by fructose 2,6-bisphosphate.

The activity of pyruvate kinase present in a crude extract of the bloodstream form of Trypanosoma brucei was greatly increased by fructose 2,6-bisphosphate, which converted the saturation curve for phosphoenolpyruvate from a sigmoid into a hyperbola with no change in V. Phosphate and arsenate had an effect opposite to that of fructose 2,6-bisphosphate and the apparent Ka for fructose 2,6-bisphosphate was shifted from 75 nM to 1.5 microM by the presence of 5 mM phosphate. Fructose 1,6-bisphosphate had effects similar to those of fructose 2,6-bisphosphate but at approximately 4000-fold higher concentrations. Pyruvate kinases of Crithidia luciliae and of Leishmania major, two trypanosomatids which are like T. brucei in containing glycosomes, were also stimulated by fructose 2,6-bisphosphate and inhibited by phosphate.