Editing Pyruvate kinase (section)

==Clinical applications==

=== Deficiency ===
Genetic defects of this enzyme cause the disease known as [[pyruvate kinase deficiency]]. In this condition, a lack of pyruvate kinase slows down the process of glycolysis. This effect is especially devastating in cells that lack [[mitochondria]], because these cells must use [[anaerobic glycolysis]] as their sole source of energy because the [[TCA cycle]] is not available. For example, [[red blood cells]], which in a state of pyruvate kinase deficiency, rapidly become deficient in ATP and can undergo [[hemolysis]]. Therefore, pyruvate kinase deficiency can cause chronic nonspherocytic [[hemolytic anemia]] (CNSHA).<ref>{{cite journal | vauthors = Grace RF, Zanella A, Neufeld EJ, Morton DH, Eber S, Yaish H, Glader B | title = Erythrocyte pyruvate kinase deficiency: 2015 status report | journal = American Journal of Hematology | volume = 90 | issue = 9 | pages = 825–30 | date = September 2015 | pmid = 26087744 | doi = 10.1002/ajh.24088 | pmc = 5053227 }}</ref>

==== PK-LR gene mutation ====
Pyruvate kinase deficiency is caused by an autosomal recessive trait. Mammals have two pyruvate kinase genes, PK-LR (which encodes for pyruvate kinase isozymes L and R) and PK-M (which encodes for pyruvate kinase isozyme M1), but only PKLR encodes for the red blood isozyme which effects pyruvate kinase deficiency. Over 250 PK-LR gene mutations have been identified and associated with pyruvate kinase deficiency. DNA testing has guided the discovery of the location of PKLR on chromosome 1 and the development of direct gene sequencing tests to molecularly diagnose pyruvate kinase deficiency.<ref>{{cite journal | vauthors = Climent F, Roset F, Repiso A, Pérez de la Ossa P | title = Red cell glycolytic enzyme disorders caused by mutations: an update | journal = Cardiovascular & Hematological Disorders Drug Targets | volume = 9 | issue = 2 | pages = 95–106 | date = June 2009 | pmid = 19519368 | doi = 10.2174/187152909788488636 }}</ref>

=== Applications of pyruvate kinase inhibition ===

==== Reactive Oxygen Species (ROS) Inhibition ====
[[Reactive oxygen species]] (ROS) are chemically reactive forms of oxygen. In human lung cells, ROS has been shown to inhibit the M2 isozyme of pyruvate kinase (PKM2). ROS achieves this inhibition by oxidizing Cys358 and inactivating PKM2. As a result of PKM2 inactivation, glucose flux is no longer converted into pyruvate, but is instead utilized in the pentose phosphate pathway, resulting in the reduction and detoxification of ROS. In this manner, the harmful effects of ROS are increased and cause greater oxidative stress on the lung cells, leading to potential tumor formation. This inhibitory mechanism is important because it may suggest that the regulatory mechanisms in PKM2 are responsible for aiding cancer cell resistance to oxidative stress and enhanced tumorigenesis.<ref>{{cite journal | vauthors = Anastasiou D, Poulogiannis G, Asara JM, Boxer MB, Jiang JK, Shen M, Bellinger G, Sasaki AT, Locasale JW, Auld DS, Thomas CJ, Vander Heiden MG, Cantley LC | title = Inhibition of pyruvate kinase M2 by reactive oxygen species contributes to cellular antioxidant responses | journal = Science | volume = 334 | issue = 6060 | pages = 1278–83 | date = December 2011 | pmid = 22052977 | pmc = 3471535 | doi = 10.1126/science.1211485 | bibcode = 2011Sci...334.1278A }}</ref><ref>{{cite journal | vauthors = Christofk HR, Vander Heiden MG, Harris MH, Ramanathan A, Gerszten RE, Wei R, Fleming MD, Schreiber SL, Cantley LC | title = The M2 splice isoform of pyruvate kinase is important for cancer metabolism and tumour growth | journal = Nature | volume = 452 | issue = 7184 | pages = 230–3 | date = March 2008 | pmid = 18337823 | doi = 10.1038/nature06734 | bibcode = 2008Natur.452..230C | s2cid = 16111842 }}</ref>

==== Phenylalanine inhibition ====
Phenylalanine is found to function as a competitive inhibitor of pyruvate kinase in the brain. Although the degree of phenylalanine inhibitory activity is similar in both fetal and adult cells, the enzymes in the fetal brain cells are significantly more vulnerable to inhibition than those in adult brain cells. A study of PKM2 in babies with the genetic brain disease [[Phenylketonuria|phenylketonurics]] (PKU), showed elevated levels of phenylalanine and decreased effectiveness of PKM2. This inhibitory mechanism provides insight into the role of pyruvate kinase in brain cell damage.<ref>{{cite journal | vauthors = Miller AL, Hawkins RA, Veech RL | title = Phenylketonuria: phenylalanine inhibits brain pyruvate kinase in vivo | journal = Science | volume = 179 | issue = 4076 | pages = 904–6 | date = March 1973 | pmid = 4734564 | doi = 10.1126/science.179.4076.904 | bibcode = 1973Sci...179..904M | s2cid = 12776382 }}</ref><ref>{{cite journal | vauthors = Weber G | title = Inhibition of human brain pyruvate kinase and hexokinase by phenylalanine and phenylpyruvate: possible relevance to phenylketonuric brain damage | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 63 | issue = 4 | pages = 1365–9 | date = August 1969 | pmid = 5260939 | pmc = 223473 | doi = 10.1073/pnas.63.4.1365 | bibcode = 1969PNAS...63.1365W | doi-access = free }}</ref>

=== Pyruvate Kinase in Cancer ===
Cancer cells have characteristically accelerated metabolic machinery and Pyruvate Kinase is believed to have a role in cancer. When compared to healthy cells, cancer cells have elevated levels of the PKM2 isoform, specifically the low activity dimer. Therefore, PKM2 serum levels are used as markers for cancer. The low activity dimer allows for build-up of phosphoenol pyruvate (PEP), leaving large concentrations of glycolytic intermediates for synthesis of biomolecules that will eventually be used by cancer cells.<ref name=":02"/> Phosphorylation of PKM2 by [[MAPK1|Mitogen-activated protein kinase 1]] (ERK2) causes conformational changes that allow PKM2 to enter the nucleus and regulate glycolytic gene expression required for tumor development.<ref>{{cite journal | vauthors = Yang W, Zheng Y, Xia Y, Ji H, Chen X, Guo F, Lyssiotis CA, Aldape K, Cantley LC, Lu Z | display-authors = 6 | title = ERK1/2-dependent phosphorylation and nuclear translocation of PKM2 promotes the Warburg effect | journal = Nature Cell Biology | volume = 14 | issue = 12 | pages = 1295–304 | date = December 2012 | pmid = 23178880 | pmc = 3511602 | doi = 10.1038/ncb2629 | first8 = Yan | first9 = Yanhua | first6 = Xiaomin | first7 = Haitao }}</ref> Some studies state that there is a shift in expression from PKM1 to PKM2 during carcinogenesis. Tumor microenvironments like hypoxia activate transcription factors like the hypoxia-inducible factor to promote the transcription of PKM2, which forms a positive feedback loop to enhance its own transcription.<ref name=":02" />[[File:Red Blood Cell abnormalities.png|right|thumb|Distribution of red blood cell abnormalities worldwide]]