The quantitative aspects of the regulation of glycolytic flux are still not well established. Even though convincing evidence that phosphofructokinase (PFK) participates in the regulation of the flux has been provided only for erythrocytes (albeit hexokinase seems to be more important in this respect), it is accepted that PFK is the main rate-controlling enzyme of glycolysis in different tissues. Some measure of participation in this control has also been suggested for both hexokinase and pyruvate kinase. The main reasons for this generalized belief are that PFK catalyses a reaction very far from equilibrium and that it exhibits a complex and sophisticated regulatory behaviour that reflects its ability to integrate many different signals from different pathways. However, as first expressed by Kacser and Burns, no single enzyme is likely to be responsible for the regulation of the metabolic flux through any pathway.

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