Phosphofructokinase from flight muscle of the cockroach, Periplaneta americana

Kinetic Characterisation of Phosphofructokinase Purified from Setaria cervi: A Bovine Filarial Parasite

Phosphofructokinase (PFK), a regulatory enzyme in glycolytic pathway, has been purified to electrophoretic homogeneity from adult female Setaria cervi and partially characterized. For this enzyme, the Lineweaver-Burk's double reciprocal plots of initial rates and D-fructose-6-phosphate (F-6-P) or Mg-ATP concentrations for varying values of cosubstrate concentration gave intersecting lines indicating that K_m values for F-6-P (1.05 mM) and ATP (3 μM) were independent of each other. S. cervi PFK, when assayed at inhibitory concentration of ATP (>0.1 mM), exhibited sigmoidal behavior towards binding with F-6-P with a Hill coefficient (n) value equal to 1.8 and 1.7 at 1.0 and 0.33 mM ATP, respectively. D-fructose-1,6-diphosphate (FDP) competitively inhibited the filarial enzyme: K_i and Hill coefficient values being 0.18 μM and 2.0, respectively. Phosphoenolpyruvate (PEP) also inhibited the enzyme competitively with the K_i value equal to 0.8 mM. The Hill coefficient values (>1.5) for F-6-P (at inhibitory concentration of ATP) and FDP suggested its positive cooperative kinetics towards F-6-P and FDP, showing presence of more than one binding sites for these molecules in enzyme protein and allosteric nature of the filarial enzyme. The product inhibition studies gave us the only compatible mechanism of random addition process with a probable orientation of substrates and products on the enzyme surface.

Phosphofructokinase from white muscle of the rainbow trout, Oncorhynchus mykiss: purification and properties

Phosphofructokinase was purified and characterized from the white skeletal muscle of rainbow trout Oncorhynchus mykiss. Purification involved three steps: ion-exchange chromatography on hydroxyapatite and affinity chromatography on phosphocellulose and ATP-agarose. A final specific activity of 75 units per mg of protein at 22 degrees C and pH 7.2 with 40% recovery was obtained. The purified enzyme gave a single band on SDS-PAGE with a subunit molecular mass of 76.5 +/- 0.6 kDa. Based on gel filtration analysis, the active form of the enzyme was found to be composed of six identical subunits. A high isoelectric point (7.1) was found for this enzyme. Arrhenius plots of the enzyme activity showed a sharp transition at 15-16 degrees C. The pH optimum of the enzyme was 8.0-8.5 at physiological level of ATP and positive modulators shifted the optimum to lower pH values. Amino-acid analysis revealed a lower content of the aromatic residues Phe, Tyr and Trp and higher level of Ser residue than in the rabbit muscle enzyme.