The oxidative decarboxylation is a part of the process of cellular respiration. It takes place in the matrix of the mitochondria. Through this process, the carboxyl group is cleaved by certain α -keto acids in a reaction sequence, and oxidizing the resulting hydroxy group of the remainder of the molecule. Possible substrates in this case pyruvate, which, for example, comes from glycolysis, or α -ketoglutarate, a metabolite of the citric acid cycle. These are enzymatically converted to acetyl -CoA and succinyl -CoA. Both products are then further processed in the TCA cycle.
The oxidative decarboxylation occurs at very large multienzyme complexes in which interacting three enzymes: a decarboxylase, an oxidoreductase and a dehydrogenase. As coenzymes thiamine pyrophosphate, coenzyme A and NAD , required as prosthetic groups FAD, and lipoic acid. The enzymatic conversion of pyruvate to acetyl-CoA is catalyzed by the pyruvate dehydrogenase complex. α -ketoglutarate is converted in the α -ketoglutarate dehydrogenase complex to succinyl -CoA. General catalyze the oxidative decarboxylation of pyruvate is shown in the example (see scheme in the image, R = H):
- The pyruvate accumulates on thiamine pyrophosphate (TPP ), a derivative of vitamin B1, to. Then the acid group of the pyruvate is eliminated as CO2, so that hydroxyethyl - TPP is formed ( step A in the diagram ). This is catalyzed by the pyruvate dehydrogenase component (E1).
- The hydroxyethyl group is transferred to lipoamide. The result is a thioester, the acetyl- dihydrolipoamide, as an oxidizing agent thus used the disulfide. The TPP is thereby regenerated ( step B). This reaction is catalyzed by the pyruvate dehydrogenase component.
- The acetyl group is transferred to coenzyme A, acetyl-CoA is produced. This is catalysed by step through the dihydrolipoyl transacetylase (E2). This is chemically transesterification ( step C).
- Lipoic acid is regenerated by dihydrolipoyl dehydrogenase (E3 ) by the enzyme-bound FAD of dihydrolipoamide is oxidized to lipoic acid (Step D). But FAD is not covalently bound enzyme.
- FAD is finally by reduction of NAD to NADH by the same dehydrogenase regenerated ( step E). Here, the electron transfer potential of FADH2 increased to NAD , as it is associated with the enzyme.
The balance of the oxidative decarboxylation of pyruvate is:
A disturbance of this metabolic reaction has serious implications, since the electron transport chain, for example, in the reduction of glucose to CO2 interrupted.
More general meaning of the term Oxidative decarboxylation
In organic chemistry, generally designated an oxidative decarboxylation reaction in which a carboxylic acid to oxidation of the carbon chain of carbon dioxide is eliminated. This can for example be done by heating or by oxidation with lead tetraacetate (Kochi reaction). In the Hunsdiecker the oxidative decarboxylation reaction to silver salts is carried out.