Editing Pyruvic acid (section)

==Biochemistry==
{{Citations needed|date=December 2023}}
Pyruvate is an important [[chemical compound]] in [[biochemistry]]. It is the output of the metabolism of [[glucose]] known as [[glycolysis]].<ref name="lehninger528">{{Cite book|title=Principles of Biochemistry|edition=5th|first1=Albert L.|first2=David L.|first3=Michael M.|last1=Lehninger|last2=Nelson|last3=Cox|publisher=W. H. Freeman and Company|location=New York, NY|year=2008|isbn=978-0-7167-7108-1|page=[https://archive.org/details/lehningerprincip00lehn_1/page/528 528]|url-access=registration|url=https://archive.org/details/lehningerprincip00lehn_1/page/528}}</ref> One molecule of [[glucose]] breaks down into two molecules of pyruvate,<ref name="lehninger528" /> which are then used to provide further energy, in one of two ways. Pyruvate is converted into [[Acetyl-CoA|acetyl-coenzyme A]], which is the main input for a series of reactions known as the [[citric acid cycle|Krebs cycle]] (also known as the citric acid cycle or tricarboxylic acid cycle). Pyruvate is also  converted to [[oxaloacetate]] by an [[anaplerotic reactions|anaplerotic reaction]], which replenishes Krebs cycle intermediates; also, the oxaloacetate is used for [[gluconeogenesis]].{{Citation needed|date=December 2023}}

These reactions are named after [[Hans Adolf Krebs]], the biochemist awarded the 1953 [[Nobel Prize]] for physiology, jointly with [[Fritz Lipmann]], for research into metabolic processes. The cycle is also known as the [[citric acid cycle]] or tricarboxylic acid cycle, because citric acid is one of the intermediate compounds formed during the reactions.{{Citation needed|date=December 2023}}

If insufficient oxygen is available, the acid is broken down [[anaerobe|anaerobically]], creating [[lactic acid|lactate]] in animals and [[ethanol]] in plants and microorganisms (and in [[carp]]<ref>{{cite book|author1=Aren van Waarde|author2=G. Van den Thillart|author3-link=Maria Verhagen|author3=Maria Verhagen|title=Surviving Hypoxia|date=1993|isbn=0-8493-4226-0|pages=157–170|chapter=Ethanol Formation and pH-Regulation in Fish|publisher=CRC Press |author1-link=Aren van Waarde|hdl=11370/3196a88e-a978-4293-8f6f-cd6876d8c428}}</ref>). Pyruvate from glycolysis is converted by [[fermentation (biochemistry)|fermentation]] to [[lactic acid|lactate]] using the [[enzyme]] [[lactate dehydrogenase]] and the [[coenzyme]] [[NADH]] in lactate [[fermentation (biochemistry)|fermentation]], or to [[acetaldehyde]] (with the enzyme [[pyruvate decarboxylase]]) and then to [[ethanol]] in [[Ethanol fermentation|alcoholic fermentation]].{{Citation needed|date=December 2023}}

Pyruvate is a key intersection in the network of [[metabolic pathway]]s. Pyruvate can be converted into [[carbohydrate]]s via [[gluconeogenesis]], to [[fatty acid]]s or energy through [[acetyl-CoA]], to the [[amino acid]] [[alanine]], and to [[ethanol]]. Therefore, it unites several key metabolic processes.{{Citation needed|date=December 2023}}

[[File:Blood values sorted by mass and molar concentration.png|thumb|450px|[[Reference ranges for blood tests]], comparing blood content of pyruvate (shown in violet near middle) with other constituents.]]

===Pyruvic acid production by glycolysis===
In the last step of [[glycolysis]], [[phosphoenolpyruvic acid|phosphoenolpyruvate]] (PEP) is converted to pyruvate by [[pyruvate kinase]].  This reaction is strongly exergonic and irreversible; in [[gluconeogenesis]], it takes two enzymes, [[pyruvate carboxylase]] and [[PEP carboxykinase]], to catalyze the reverse transformation of pyruvate to PEP.{{Citation needed|date=December 2023}}
{{Enzymatic reaction
| forward_enzyme=[[pyruvate kinase]]
| reverse_enzyme=[[pyruvate carboxylase]] and [[PEP carboxykinase]]
| substrate=[[phosphoenolpyruvate]]
| product=pyruvic acid
| reaction_direction_(forward/reversible/reverse)=reversible
| minor_forward_substrate(s)=[[Adenosine diphosphate|ADP]]
| minor_forward_product(s)=[[adenosine triphosphate|ATP]]
| minor_reverse_substrate(s)=[[adenosine triphosphate|ATP]]
| minor_reverse_product(s)=[[Adenosine diphosphate|ADP]]
| substrate_image=phosphoenolpyruvate_wpmp.svg
| product_image=Pyruvic-acid-2D-skeletal.svg
| product_image_size=90px
}}
{{KEGG compound|C00074}} {{KEGG enzyme|2.7.1.40}} {{KEGG compound|C00022}}

{{GlycolysisGluconeogenesis_WP534|highlight=Pyruvic_acid__alt1}}

===Decarboxylation to acetyl CoA===
[[Pyruvate decarboxylation]] by the [[pyruvate dehydrogenase complex]] produces [[acetyl-CoA]].
{{Enzymatic Reaction
| forward_enzyme=[[pyruvate dehydrogenase complex]]
| reverse_enzyme=
| substrate=pyruvate
| product=[[acetyl-CoA]]
| reaction_direction_(forward/reversible/reverse)=forward
| minor_forward_substrate(s)= [[Coenzyme A|CoA]] '''+''' NAD<sup>+</sup>
| minor_forward_product(s)= CO<sub>2</sub> '''+''' NADH '''+''' H<sup>+</sup>
| minor_reverse_substrate(s)=
| minor_reverse_product(s)=
| substrate_image=pyruvate_wpmp.png
| product_image=Acetyl-CoA.svg
}}

===Carboxylation to oxaloacetate===
Carboxylation by [[pyruvate carboxylase]] produces [[oxaloacetic acid|oxaloacetate]].
{{Enzymatic Reaction
| forward_enzyme=[[pyruvate carboxylase]]
| reverse_enzyme=
| substrate=pyruvate
| product=[[oxaloacetate]]
| reaction_direction_(forward/reversible/reverse)=forward
| minor_forward_substrate(s)= ATP '''+''' CO<sub>2</sub>
| minor_forward_product(s)= ADP '''+''' P<sub>i</sub>
| minor_reverse_substrate(s)=
| minor_reverse_product(s)=
| substrate_image=pyruvate_wpmp.png
| product_image=Oxaloacetate_wpmp.png
}}

===Transamination to alanine===
Transamination by [[alanine transaminase]] produces [[alanine]].
{{Enzymatic Reaction
| forward_enzyme=[[alanine transaminase]]
| reverse_enzyme=
| substrate=pyruvate
| product=[[alanine]]
| reaction_direction_(forward/reversible/reverse)=reversible
| minor_forward_substrate(s)= [[glutamate]]
| minor_forward_product(s)= [[α-ketoglutarate]]
| minor_reverse_substrate(s)= [[α-ketoglutarate]]
| minor_reverse_product(s)= [[glutamate]]
| substrate_image=pyruvate_wpmp.png
| product_image=L-alanine-skeletal.svg
| product_image_size=100px
}}

===Reduction to lactate===
Reduction by [[lactate dehydrogenase]] produces [[lactic acid|lactate]].
{{Enzymatic Reaction
| forward_enzyme=[[lactate dehydrogenase]]
| reverse_enzyme=
| substrate=pyruvate
| product=[[lactic acid|lactate]]
| reaction_direction_(forward/reversible/reverse)=reversible
| minor_forward_substrate(s)= NADH
| minor_forward_product(s)= NAD<sup>+</sup>
| minor_reverse_substrate(s)= NAD<sup>+</sup>
| minor_reverse_product(s)= NADH
| substrate_image=pyruvate_wpmp.png
| product_image=Lactic-acid-skeletal.svg
}}

=== Environmental chemistry ===
Pyruvic acid is an abundant carboxylic acid in [[secondary organic aerosol]]s.<ref>{{Cite journal|last1=Guzman|first1=Marcelo I.|last2=Eugene|first2=Alexis J.|date=2021-09-01|title=Aqueous Photochemistry of 2-Oxocarboxylic Acids: Evidence, Mechanisms, and Atmospheric Impact|journal=Molecules|language=en|volume=26|issue=17|page=5278|doi=10.3390/molecules26175278|pmid=34500711|pmc=8433822|doi-access=free}}</ref>