Allostenic enzymes at certain points in the respiration pathway respond to inhibitors and activators that hlep set the pace of glycolysis and the Krebs cycle. Phosphofructokinase, the enzyme that catalyzes step 3 of glycolysis, is one such enzyme. It is inhibited by ATP and by citrate. This feedback regulation adjusts the rate of respiration as the cell's catabolic and anabolie demands change.