Pyruvate decarboxylation (also known as the Swanson Conversion, 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 .
The reaction in eukaryotes
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 184.108.40.206) has been characterized from the flagellate protist Euglena gracilis. The enzyme contained 2 molecules of FAD and 8 molecules of iron, and was thiamin diphosphate-dependent.
The reaction in prokaryotes
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 220.127.116.11) that uses an iron-sulfur protein as the electron acceptor instead of NAD+ or NADP+. The enzyme is thiamine-dependent. The reducing equivalents are disposed of by the production of H2 via hydrogenase.
The steps involved in this reaction comprise:
1. Pyruvate is decarboxylated
is ready to enter the citric acid cycle.
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- 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.
- KEGG pathway database
- MetaCyc pathway: pyruvate decarboxylation to acetyl CoA
- Notes on pyruvate decarboxylation