Selforganization of a glycoltylic reconstituted enzyme system: Alternate stable stationary states, hysteretic transitions and stabilization of the energy charge

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The dynamic behavior of a homogeneous open enzyme system reconstituted from phosphofructokinase, pyruvate kinase, adenylate kinase and glucose-6-phosphate isomerase has been analyzed in respect to the appearance of alternative stable stationary states and related dynamic phenomena. The approach is experimentally based on a stirred enzyme reactor containing gel entrapped phosphofructokinase and pyruvate kinase. Through the reactor a flow of reactants as well as of adenylate kinase and glucose-6-phosphate isomerase is continuously maintained. The kinetic properties of the system are analyzed by a mathematical model based on the initial kinetic properties of the individual enzymes involved as well as on the essentials of the experimental procedure. The theoretical analysis demonstrates the occurrence of nonlinear dynamic phenomena originating from the allosteric properties of phosphofructokinase, especially from its activation by AMP. In a wide range of experimental conditions alternate stable steady states are predicted which imply the possibility of jumps and the existence of hysteresis. In fact, multiple stationary states could be shown experimentally. The system has been found to exhibit a trigger behavior caused by hysteretic transitions between alternate stable steady states. The hysteretic transitions which have been induced by perturbations of the environment may invert the dynamic regime from ATP consumption to ATP generation and vice versa. As a consequence of the intrinsic nonlinear interactions and of the existence of alternate stable steady states the stationary energy charge can efficiently be stabilized in a wide range of external conditions.