Editing Pyruvate kinase (section)

=== Glycolysis ===
There are two steps in the pyruvate kinase reaction in glycolysis. First, PEP transfers a phosphate group to ADP, producing ATP and the [[Enolate anion|enolate]] of pyruvate. Secondly, a proton must be added to the enolate of pyruvate to produce the functional form of pyruvate that the cell requires.<ref>{{cite journal | vauthors = Kumar S, Barth A | title = Phosphoenolpyruvate and Mg2+ binding to pyruvate kinase monitored by infrared spectroscopy | language = en | journal = Biophysical Journal | volume = 98 | issue = 9 | pages = 1931–40 | date = May 2010 | pmid = 20441757 | pmc = 2862152 | doi = 10.1016/j.bpj.2009.12.4335 | bibcode = 2010BpJ....98.1931K }}</ref> Because the substrate for pyruvate kinase is a simple phospho-sugar, and the product is an ATP, pyruvate kinase is a possible foundation enzyme for the evolution of the glycolysis cycle, and may be one of the most ancient enzymes in all earth-based life. Phosphoenolpyruvate may have been present abiotically, and has been shown to be produced in high yield in a primitive triose glycolysis pathway.<ref>{{cite journal | vauthors = Coggins AJ, Powner MW | title = Prebiotic synthesis of phosphoenol pyruvate by α-phosphorylation-controlled triose glycolysis | journal = Nature Chemistry | volume = 9 | issue = 4 | pages = 310–317 | date = April 2017 | pmid = 28338685 | doi = 10.1038/nchem.2624 | s2cid = 205296677 | url = https://discovery.ucl.ac.uk/id/eprint/1520873/ }}</ref>
[[Image:Pyruvate kinase.png|left|thumb|255x255px|A simple diagram demonstrating the final step of glycolysis, the transfer of a phosphate group from [[phosphoenolpyruvate]] (PEP) to [[adenosine diphosphate]] (ADP) by pyruvate kinase, yielding one molecule of [[pyruvate]] and one molecule of [[Adenosine triphosphate|ATP]].]]In yeast cells, the interaction of yeast pyruvate kinase (YPK) with PEP and its allosteric effector [[Fructose 1,6-bisphosphate]] (FBP,) was found to be enhanced by the presence of Mg<sup>2+</sup>. Therefore, Mg<sup>2+</sup> was concluded to be an important cofactor in the catalysis of PEP into pyruvate by pyruvate kinase. Furthermore, the metal ion Mn<sup>2+</sup> was shown to have a similar, but stronger effect on YPK than Mg<sup>2+</sup>. The binding of metal ions to the metal binding sites on pyruvate kinase enhances the rate of this reaction.<ref>{{cite journal | vauthors = Bollenbach TJ, Nowak T | title = Kinetic linked-function analysis of the multiligand interactions on Mg(2+)-activated yeast pyruvate kinase | journal = Biochemistry | volume = 40 | issue = 43 | pages = 13097–106 | date = October 2001 | pmid = 11669648 | doi = 10.1021/bi010126o }}</ref> 
The reaction catalyzed by pyruvate kinase is the final step of glycolysis. It is one of three rate-limiting steps of this pathway. [[Rate-determining step|Rate-limiting steps]] are the slower, regulated steps of a pathway and thus determine the overall rate of the pathway. In glycolysis, the rate-limiting steps are coupled to either the hydrolysis of ATP or the phosphorylation of ADP, causing the pathway to be energetically favorable and essentially irreversible in cells. This final step is highly regulated and deliberately irreversible because pyruvate is a crucial intermediate building block for further metabolic pathways.<ref name = "Berg_2002">{{cite book | vauthors = Berg JM, Tymoczko JL, Stryer J, Clarke ND | title = Biochemistry | date = 2002 | publisher = W.H. Freeman | location = New York, NY | isbn = 978-0-7167-3051-4 | edition = fifth | url = https://archive.org/details/biochemistrychap00jere | url-access = registration }}</ref> Once pyruvate is produced, it either enters the [[Citric acid cycle|TCA cycle]] for further production of ATP under aerobic conditions, or is converted to [[lactic acid]] or [[ethanol]] under anaerobic conditions.