Transitions between alternate ATP-producing and ATP-consuming stationary states in a reconstituted enzyme system containing phosphofructokinase.

The kinetic behavior of a reconstituted eyzyme system containing purified phosphofructokinase, pyruvate kinase, adenylate kinase, and glucose 6-phosphate isomerase was investigated. Experimentally the approach is based on a stirred flow-through reactor containing gel entrapped enzymes. The experiments were performed on the basis of a mathematical model developed from the kinetic properties of the individual enzymes involved. The system is able to exhibit alternative stable stationary states for one set of experimental conditions (bistability) originating mainly from the allosteric character of the phosphofructokinase. From a functional point of view, these states are either ATP-generating or ATP-consuming. Theoretically, the appearance of alternate steady states gives rise to hysteretic behavior of the system. In fact, transitions between alternate ATP generating stationary states as well as between ATP-generating and ATP-consuming steady states were observed experimentally.