Phosphofructokinase-1 (PFK-1) is an important enzyme in the process of glycolysis, which is how cells break down glucose to produce energy. It catalyzes a key step by converting fructose-6-phosphate into fructose-1,6-bisphosphate, using ATP as a phosphate donor. This reaction is a major regulatory point in glycolysis, meaning it helps control the flow of glucose through this metabolic pathway. PFK-1 is regulated by various molecules, including ATP, ADP, and citrate. High levels of ATP indicate that the cell has enough energy, which inhibits PFK-1 activity, while high levels of ADP signal a need for more energy, activating the enzyme. This regulation ensures that energy production matches the cell's needs.