| Type: | Active_site | Name: | Pyruvate kinase, active site |
| Description: | Pyruvate kinase () (PK) catalyses the final step in glycolysis [], the conversion of phosphoenolpyruvate to pyruvate with concomitant phosphorylation of ADP to ATP:ADP + phosphoenolpyruvate = ATP + pyruvate The enzyme, which is found in all living organisms, requires both magnesium and potassium ions for its activity. In vertebrates, there are four tissue-specific isozymes: L (liver), R (red cells), M1 (muscle, heart and brain), and M2 (early foetal tissue). In plants, PK exists as cytoplasmic and plastid isozymes, while most bacteria and lower eukaryotes have one form, except in certain bacteria, such as Escherichia coli, that have two isozymes. All isozymes appear to be tetramers of identical subunits of ~500 residues.PK helps control the rate of glycolysis, along with phosphofructokinase () and hexokinase (). PK possesses allosteric sites for numerous effectors, yet the isozymes respond differently, in keeping with their different tissue distributions []. The activity of L-type (liver) PK is increased by fructose-1,6-bisphosphate (F1,6BP) and lowered by ATP and alanine (gluconeogenic precursor), therefore when glucose levels are high, glycolysis is promoted, and when levels are low, gluconeogenesis is promoted. L-type PK is also hormonally regulated, being activated by insulin and inhibited by glucagon, which covalently modifies the PK enzyme. M1-type (muscle, brain) PK is inhibited by ATP, but F1,6BP and alanine have no effect, which correlates with the function of muscle and brain, as opposed to the liver.The structure of several pyruvate kinases from various organisms have been determined [, ]. The protein comprises three-four domains: a small N-terminal helical domain (absent in bacterial PK), a beta/alpha-barrel domain, a beta-barrel domain (inserted within the beta/alpha-barrel domain), and a 3-layer alpha/beta/alpha sandwich domain.This entry represents an active site that includes a lysine residue which seems to be the acid/base catalyst responsible for the interconversion of pyruvate and enolpyruvate, and a glutamic acid residue implicated in the binding of the magnesium ion. | Short Name: | Pyrv_Knase_AS |
