ATP-Catalyzed Preconditioning of Phosphofructokinase

Abstract

Phosphofructokinase (EC 2.7.1.11) is subject to inactivation (at pH values below 6) and reactivation (at alkaline pH) to forms that correspond, respectively, to immature and mature conformational states. ATP is one of several ligands that facilitate the reactivation process, which we have termed preconditioning (1, 2). Evidence is presented that the role of ATP is a catalytic one: (a) the continued presence of ATP is not required to maintain the reactivated state; and (b) conditions can be found under which ATP catalyzes both activation and inactivation. The findings support the concept that a small molecule can catalyze changes in the conformation of a macromolecule. The correct refolding of phosphofructokinase competes with the folding of the enzyme to an inactive species. Thus, the effect of ATP on reactivation is reflected in enhancement not only of the rate, but also of the extent, of reactivation. That is, the ligand subjects the system to an irreversible commitment.