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 10-750 microgram/mL. The sedimentation properties of phosphofructokinase were analyzed by theoretical simulations or an associating system in rapid equilibrium. In the absence of any ligands and at a temperature of 23 degrees C, the simplest computed model which gives the best fit between theoretical and experimental points can be described as progressive association of monomer in equilibrium or formed from tetramer in equilibrium or formed from 16-mer with apparent equilibrium constants K4 = 5.06 X 10(5) (mL/mg)3 and K16 = 3.25 X 10(23) (mL/mg)15. However, at 5 degrees C, the equilibrium was altered and can best be described as monomer in equilibrium or formed from dimer in equilibrium or formed from tetramer in equilibrium or formed from 16-mer.