Relationships between association state and enzymic activity of human erythrocyte phosphofructokinase

Human erythrocyte phosphofructokinase has been subjected to active band centrifugation and stability measurements over a broad range of conditions. The enzyme behaves differently in-Tris buffer containing ATP and phosphate buffer containing fructose 6-phosphate. In the first buffer, dissociation is favoured and after prolonged storage of the enzyme tetramers represent the highest state of association. At 4 degrees C the enzyme exhibits the phenomenon of reversible cold-inactivation. This property is attributed to slow dissociation of the active associated states of the enzyme to dimers. The cold-inactivated enzyme can be reactivated by fructose 1,6-bisphosphate. Inorganic phosphate and fructose 6-phosphate have been found to protect the enzyme from cold-inactivation. Under these conditions, the sedimentation coefficient and the specific activity depend on the enzyme concentration only. The specific activity does not change on storage of the diluted enzyme at 4 degrees C. At 20 degrees C, however, a slow activation proceeds during incubation of the diluted enzyme. The correlations between the association state and the enzymic activity are discussed.