The dynamic pattern of an open, reconstituted in vitro enzyme system containing [yeast] phosphofructokinase, pyruvate kinase and adenylate kinase was investigated. The approach is experimentally based on a stirred flow-through reactor. Stationary concentrations of phosphofructokinase and pyruvate kinase are maintained by entrapment in polyacrylamide gel particles. The results fit to a theoretical model based on the initial kinetic responses of the enzymes involved. An S-shaped steady state input characteristic for fructose 6-phosphate was experimentally obtained.