What is considered the rate-limiting enzyme in glycolysis?

Phosphofructokinase is recognized as the rate-limiting enzyme in glycolysis due to its pivotal role in controlling the flow of metabolites through this metabolic pathway. It catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, utilizing ATP in the process. This step is not only irreversible but also represents a crucial regulatory point in glycolysis, where the activity of phosphofructokinase can be modulated by various factors including levels of ATP, ADP, AMP, and citrate.

This regulatory mechanism ensures that glycolysis responds appropriately to the energy needs of the cell. When energy demand is high (indicated by elevated ADP or AMP levels), phosphofructokinase is activated, promoting glycolytic flux. Conversely, when energy is plentiful (indicated by high ATP and citrate levels), its activity is inhibited, slowing down the pathway.

While other enzymes such as hexokinase and pyruvate kinase play important roles in glycolysis, they do not have the same level of regulation or impact on the overall flow through the pathway as phosphofructokinase does. Thus, phosphofructokinase is rightly identified as the rate-lim