Editing Pyruvate kinase (section)

=== Gluconeogenesis: the reverse reaction ===
Pyruvate kinase also serves as a regulatory enzyme for [[gluconeogenesis]], a biochemical pathway in which the liver generates [[glucose]] from pyruvate and other substrates. Gluconeogenesis utilizes noncarbohydrate sources to provide glucose to the brain and red blood cells in times of starvation when direct glucose reserves are exhausted.<ref name = "Berg_2002" /> During [[fasting state]], pyruvate kinase is inhibited, thus preventing the "leak-down" of [[Phosphoenolpyruvic acid|phosphoenolpyruvate]] from being converted into pyruvate;<ref name="Berg_2002" /> instead, phosphoenolpyruvate is converted into glucose via a cascade of [[gluconeogenesis]] reactions. Although it utilizes similar enzymes, gluconeogenesis is not the reverse of glycolysis. It is instead a pathway that circumvents the irreversible steps of glycolysis. Furthermore, gluconeogenesis and glycolysis do not occur concurrently in the cell at any given moment as they are reciprocally regulated by cell signaling.<ref name="Berg_2002" /> Once the gluconeogenesis pathway is complete, the glucose produced is expelled from the liver, providing energy for the vital tissues in the fasting state.