Trypsin modification of phosphofructokinase from Ascaris suum.

Phosphofructokinase from Ascaris suum is a tetramer with subunits of 90 kDa. Treatment of the native enzyme with trypsin (10%, w/w) followed by SDS-gel electrophoresis was shown to immediately generate a 40-kDa fragment followed by a gradual formation of two other fragments of 37 and 32 kDa. The loss of catalytic activity during the digestion was less than 50%. Gel filtration of the digested enzyme under non-denaturing conditions showed a Mr almost that of the native enzyme. Digestion of the phosphorylated enzyme resulted in an 80% release of the phosphorylated peptide over the period of 1 h. The digested enzyme was inhibited less by ATP than the native enzyme, but it was still positively affected by the effectors, fructose 2,6-bisphosphate and AMP. The results are interpreted to suggest that the structure of the ascarid phosphofructokinase is similar to that of the mammalian enzyme.