Oxidative decarboxylation
Encyclopedia
Pyruvate decarboxylation (also known as the Naypyidaw Reaction, Swanson Conversion, or oxidative decarboxylation 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
. It is known as the link reaction because it forms an important link between the metabolic pathway
s of glycolysis
and the citric acid cycle
. This reaction is usually catalyzed by the pyruvate dehydrogenase complex as part of aerobic respiration. In eukaryotes, pyruvate decarboxylation takes place exclusively inside the mitochondrial matrix; in prokaryotes similar reactions take place in the cytoplasm and at the plasma membrane.
This reaction is very common in most organisms as a link to the citric acid cycle
. This reaction is carried out in the mitochondria, unlike the reactions of glycolysis which are cytosol
ic.
The conversion of pyruvate to acetyl CoA by the pyruvate dehydrogenase complex is a key step in the liver in particular, as it removes any chance of conversion of pyruvate to glucose, or as a transamination substrate. It commits pyruvate to entering the citric acid cycle, where it is either used as a substrate for oxidative phosphorylation
, or is converted to citrate
for export to the cytosol to serve as a substrate for fatty acid
and isoprenoid biosynthesis.
The oxidative decarboxylation of pyruvate in anaerobic organisms differs from the aerobic process in that the electron acceptor is an iron-sulfur protein
, not NAD+. The conversion is catalyzed by a thiamine
-dependent enzyme that also acylates coenzyme A. The reducing equivalents are disposed of by the production of H2 via hydrogenase.
Acetyl-CoA
Acetyl coenzyme A or acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production. In chemical structure, acetyl-CoA is the thioester...
, releasing NADH, a reducing equivalent, and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
via decarboxylation
Decarboxylation
Decarboxylation is a chemical reaction that releases carbon dioxide . Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carbonation, the addition of CO2 to...
. It is known as the link reaction because it forms an important link between the metabolic pathway
Metabolic pathway
In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function...
s of glycolysis
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
and the citric acid cycle
Citric acid cycle
The citric acid cycle — also known as the tricarboxylic acid cycle , the Krebs cycle, or the Szent-Györgyi-Krebs cycle — is a series of chemical reactions which is used by all aerobic living organisms to generate energy through the oxidization of acetate derived from carbohydrates, fats and...
. This reaction is usually catalyzed by the pyruvate dehydrogenase complex as part of aerobic respiration. In eukaryotes, pyruvate decarboxylation takes place exclusively inside the mitochondrial matrix; in prokaryotes similar reactions take place in the cytoplasm and at the plasma membrane.
This reaction is very common in most organisms as a link to the citric acid cycle
Citric acid cycle
The citric acid cycle — also known as the tricarboxylic acid cycle , the Krebs cycle, or the Szent-Györgyi-Krebs cycle — is a series of chemical reactions which is used by all aerobic living organisms to generate energy through the oxidization of acetate derived from carbohydrates, fats and...
. This reaction is carried out in the mitochondria, unlike the reactions of glycolysis which are cytosol
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
ic.
The conversion of pyruvate to acetyl CoA by the pyruvate dehydrogenase complex is a key step in the liver in particular, as it removes any chance of conversion of pyruvate to glucose, or as a transamination substrate. It commits pyruvate to entering the citric acid cycle, where it is either used as a substrate for oxidative phosphorylation
Oxidative phosphorylation
Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all aerobic organisms carry out oxidative phosphorylation to produce ATP,...
, or is converted to citrate
Citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...
for export to the cytosol to serve as a substrate for fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
and isoprenoid biosynthesis.
The oxidative decarboxylation of pyruvate in anaerobic organisms differs from the aerobic process in that the electron acceptor is an iron-sulfur protein
Iron-sulfur protein
Iron-sulfur proteins are proteins characterized by the presence of iron-sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states...
, not NAD+. The conversion is catalyzed by a thiamine
Thiamine
Thiamine or thiamin or vitamin B1 , named as the "thio-vitamine" is a water-soluble vitamin of the B complex. First named aneurin for the detrimental neurological effects if not present in the diet, it was eventually assigned the generic descriptor name vitamin B1. Its phosphate derivatives are...
-dependent enzyme that also acylates coenzyme A. The reducing equivalents are disposed of by the production of H2 via hydrogenase.
To summarise:
1. Pyruvate is decarboxylated
2. It is added to CoACoenzyme ACoenzyme A is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle. All sequenced genomes encode enzymes that use coenzyme A as a substrate, and around 4% of cellular enzymes use it as a substrate...
to form Acetyl CoA
Acetyl CoA is then ready for use in the Krebs Cycle.