PURIFICATION AND REGULATORY PROPERTIES OF PHOSPHOFRUCTOKINASE FROM TRYPANOSOMA (TRYPANOZOON) BRUCEI-BRUCEI

Phosphofructokinase (EC 2.7.1.11) from T. b. brucei was purified to homogeneity by using a 3-step procedure that may be performed within 1 day. Proteolysis, which removes a fragment of MW .apprx. 2000, may occur during the purification, but this can be prevented by including antipain, an inhibitor of cysteine proteinases, in the buffers during the purification. The subunits of the enzyme appear to be identical in size with a MW of 49,000. The MW of the native enzyme was estimated to be .apprx. 220,000, suggesting a tetrameric structure. Kinetic studies showed the activity to depend hyperbolically on the concentration of ATP but sigmoidally on the concentration of fructose-6-phosphate. Although cAMP, AMP and ADP stimulated the enzyme activity at low concentrations of fructose-6-phosphate, the last 2 nucleotides were inhibitory at high concentrations of this substrate. Phosphoenolpyruvate behaved as an allosteric inhibitor of the phosphofructokinase. Citrate, fructose 1,6-bisphosphate, fructose 2,6-bisphosphate and Pi did not influence significantly the activity of the enzyme.