Pyruvate decarboxylation

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Pyruvate decarboxylation (also known as the Swanson Conversion,[1] oxidative decarboxylation reaction or link reaction) is the far from equilibrium biochemical reaction that uses pyruvate to form acetyl-CoA, releasing NADH, a reducing equivalent, and carbon dioxide via decarboxylation. This reaction is very common in most organisms as a link between glycolysis and the citric acid cycle. In organisms that perform aerobic respiration the reaction is usually catalyzed by the pyruvate dehydrogenase complex .[1]

pyruvate (Pyr) pyruvate dehydrogenase complex (PDHC) acetyl CoA (Ac-CoA)
Pyruvate2 wpmp.png   Acetyl co-A wpmp small.png
CoA + NAD+ CO2 + NADH + H+
Biochem reaction arrow forward YYNN horiz med.png
 
 

The reaction in eukaryotes[edit]

In eukaryotes, pyruvate decarboxylation takes place exclusively inside the mitochondrial matrix, unlike the reactions of glycolysis, which are cytosolic.[2]

Most eukaryotic organisms possess an NAD+-dependent pyruvate dehydrogenase complex. In mammals the conversion of pyruvate to acetyl CoA by this enzyme is a key step in the liver in particular, as it prevents the conversion of pyruvate to glucose or its serving as a transamination substrate. Once formed, acetyl-CoA is committed to enter the citric acid cycle, where it is either used as a substrate for oxidative phosphorylation, or exported to the cytosol in the form of citrate to serve as a substrate for fatty acid and isoprenoid biosynthesis.

An NADP+-dependent, oxygen-sensitive pyruvate decarboxylase (EC 1.2.1.51) has been characterized from the flagellate protist Euglena gracilis.[3] The enzyme contained 2 molecules of FAD and 8 molecules of iron, and was thiamin diphosphate-dependent.

The reaction in prokaryotes[edit]

The decarboxylation of pyruvate in prokaryotes takes place in the cytoplasm and at the plasma membrane. Most aerobic bacteria possess a pyruvate dehydrogenase complex with similar functionality to the eukaryotic enzyme. Anaerobic organisms utilize a different enzyme (pyruvate synthase, EC 1.2.7.1) that uses an iron-sulfur protein as the electron acceptor instead of NAD+ or NADP+. The enzyme is thiamine-dependent.[4] The reducing equivalents are disposed of by the production of H2 via hydrogenase.

Summary[edit]

The steps involved in this reaction comprise:

1. Pyruvate is decarboxylated

2. The resulting acetyl moiety is added to CoA to form Acetyl CoA, which

is ready to enter the citric acid cycle.

Pyruvate decarboxylation steps

References[edit]

  1. ^ a b Alberts et al. Molecular Biology of the Cell. Garland Science, 2001. ISBN 0-8153-4072-9
  2. ^ Raven et al. Biology, 8th edition. McGraw Hill, 2008. ISBN 978-0-07-110202-5
  3. ^ Inui, H; Ono, K; Miyatake, K; Nakano, Y; Kitaoka, S (1987). "Purification and characterization of pyruvate:NADP+ oxidoreductase in Euglena gracilis". The Journal of biological chemistry 262 (19): 9130–5. PMID 3110154.  edit
  4. ^ Eric Chabrière, Xavier Vernède, Bruno Guigliarelli, Marie-Hélène Charon, E. Claude Hatchikian, Juan C. Fontecilla-Camps “Crystal Structure of the Free Radical Intermediate of Pyruvate:Ferredoxin Oxidoreductase” Science 2001, Volume 294, page 2559.

External links[edit]