Editing Pentose phosphate pathway (section)

{{Short description|Series of interconnected biochemical reactions}}
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[[File:Pentose phosphate pathway en.svg|thumb|right|400px|class=skin-invert-image|The pentose phosphate pathway]]
The '''pentose phosphate pathway''' (also called the '''phosphogluconate pathway''' and the '''hexose monophosphate shunt''' or '''HMP shunt''') is a [[metabolic pathway]] parallel to [[glycolysis]].<ref name="Alfarouk 2020">{{cite journal |last1=Alfarouk |first1=Khalid O. |last2=Ahmed |first2=Samrein B. M. |last3=Elliott |first3=Robert L. |display-authors=etal |title=The Pentose Phosphate Pathway Dynamics in Cancer and Its Dependency on Intracellular pH |journal=Metabolites |date=2020 |volume=10 |page=285 |doi=10.3390/metabo10070285 |pmid=32664469 |pmc=7407102 |doi-access=free }}</ref> It generates [[Nicotinamide adenine dinucleotide phosphate|NADPH]] and [[pentose]]s (five-[[carbon]] [[sugar]]s) as well as [[ribose 5-phosphate]], a precursor for the synthesis of [[nucleotides]].<ref name="Alfarouk 2020" /> While the pentose phosphate pathway does involve oxidation of [[glucose]], its primary role is [[anabolism|anabolic]] rather than [[catabolism|catabolic]]. The pathway is especially important in [[red blood cell]]s (erythrocytes). The reactions of the pathway were elucidated in the early 1950s by [[Bernard Horecker]] and co-workers.<ref>{{cite journal | title= The enzymatic conversion of 6-phosphogluconate to ribulose-5-phosphate and ribose-5-phosphate|journal = J. Biol. Chem. | last1 = Horecker| first1 = B. L.| last2 = Smyrniotis|first2 =P. Z.|last3= Seegmiller|first3 = J. E.|year = 1951|volume = 193|number = 1 |pages = 383–396|doi = 10.1016/S0021-9258(19)52464-4 |doi-access = free |pmid = 14907726 }}</ref><ref>{{cite journal | journal = J. Biol. Chem.| doi=10.1074/jbc.X200007200 |year = 2002|volume = 277|number =  50| pages = 47965–47971|title = The pentose phosphate pathway|doi-access = free | last1=Horecker | first1=Bernard L. | pmid=12403765 }}</ref>

There are two distinct phases in the pathway. The first is the [[oxidation|oxidative]] phase, in which NADPH is generated, and the second is the non-oxidative [[Chemical synthesis|synthesis]] of five-carbon sugars. For most organisms, the pentose phosphate pathway takes place in the [[cytosol]]; in plants, most steps take place in [[plastid]]s.<ref>{{cite journal|last1=Kruger|first1=Nicholas J|last2=von Schaewen|first2=Antje|title=The oxidative pentose phosphate pathway: structure and organisation|journal=Current Opinion in Plant Biology|date=June 2003|volume=6|issue=3|pages=236–246|doi=10.1016/S1369-5266(03)00039-6|pmid=12753973|bibcode=2003COPB....6..236K }}</ref>

Like [[glycolysis]], the pentose phosphate pathway appears to have a very ancient evolutionary origin. The reactions of this pathway are mostly enzyme catalyzed in modern cells, however, they also occur non-enzymatically under conditions that replicate those of the [[Archean]] ocean, and are catalyzed by [[metal ions]], particularly [[ferrous]] ions (Fe(II)).<ref>{{cite journal|last1=Keller|first1=Markus A.|last2=Turchyn|first2=Alexandra V.|last3=Ralser|first3=Markus|title=Non-enzymatic glycolysis and pentose phosphate pathway-like reactions in a plausible Archean ocean|journal=Molecular Systems Biology|date=25 April 2014|volume=10|issue=4|pages=725|doi=10.1002/msb.20145228|url= |pmid=24771084|pmc=4023395}}</ref> This suggests that the origins of the pathway could date back to the prebiotic world.