- The primary regulatory step in glycolysis is catalyzed by the enzyme Phosphofructokinase-1 (PFK-1).
- This enzyme controls the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, which is a key committed step in the glycolytic pathway.

- PFK-1 is tightly regulated to ensure cellular energy needs are met efficiently.
- One of the most important regulatory mechanisms is its allosteric inhibition by high levels of ATP.
- When ATP concentrations are abundant, PFK-1 activity is decreased, signaling that the cell has sufficient energy and slowing down glycolysis.
- Conversely, when ATP levels are low and AMP levels rise, PFK-1 is activated to increase glycolytic flux and produce more ATP.

- Other enzymes like hexokinase and pyruvate kinase also play roles in glycolysis but are not the primary regulatory sites affected by ATP levels to the same extent.
- Glyceraldehyde-3-phosphate dehydrogenase catalyzes a later step and is not a main regulatory point.

In summary, PFK-1 serves as the major rate-limiting enzyme in glycolysis, and its allosteric inhibition by ATP ensures that the cell conserves resources and maintains energy homeostasis.

Reference: Lehninger Principles of Biochemistry, 7th Edition, Chapter 14: Glycolysis and Gluconeogenesis