There are three primary rate-determining enzymes in cellular respiration. These enzymes catalyze the rate-limiting steps, which are the slowest reactions in the series. The rate determining enzyme in glycolysis is phosphofructokinase-1, or PFK-1, which converts fructose-6-phosphate to fructose-1,6-bisphosphate. It is stimulated by AMP, fructose-2,6-bisphosphate, and inhibited by ATP and citrate. Pyruvate oxidation only uses pyruvate dehydrogenase, which is activated by increased NAD+, ADP, or Ca2+. In the TCA cycle, the rate determining enzyme is isocitrate dehydrogenase, which converts isocitrate to ɑ-ketoglutarate. The specific reaction is stimulated by ADP and inhibited by ATP and NADH.