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°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°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