Pyruvate kinase catalyzes the third irreversible move in glycolysis. It is activated by fructose 1, 6-bisphosphate. The ATP and amino acid alanine allosterically inhibit the enzyme so which glycolysis slows when supplies of biosynthetic precursors and ATP (indicated by the levels of Ala) are already sufficiently high. Additionally, in a control similar to that for PFK, when the blood glucose concentration is low, glucagon is stimulates and released phosphorylation of the enzyme by a cAMP cascade. This covalent modification inhibits the enzyme so in which glycolysis slows down in times of low blood glucose levels.