Self-Association of Rabbit Muscle Phosphofructokinase at pH 7.0: Stoichiometry

The self-association of rabbit muscle phosphofructokinase at pH 7.0 was investigated by velocity sedimentation. The process was demonstrated to be in a rapid, dynamic equilibrium. The concentration dependence of the weight-average sedimentation coefficient was monitored within the range of 10-750µg/mL. The sedimentation properties of phosphofructokinase were analyzed by theoretical simulations for an associating system in rapid equilibrium. In the absence of any ligands and at a temperature of 23 °C, the simplest computed model which gives the best fit between theoretical and experimental points can be described as progressive association of monomer ̿ tetramer - 16-mer with apparent equilibrium constants K16 = 5.06 X 105 (mL/mg)3 and K16 = 3.25 X 1023 (mL/mg)15. However, at 5 °C, the equilibrium was altered and can best be described as monomer ̿ dimer ̿ tetramer ̿ 16-mer.