Localization of Pyruvate Decarboxylation
In eukaryotic cells the Swanson conversion occurs inside the mitochondria, after transport of the substrate, pyruvate, from the cytosol. The transport of pyruvate into the mitochondria is via a transport protein and is active, consuming energy. Passive diffusion of pyruvate into the mitochondria is impossible because it carries a negative charge.
On entry to the mitochondria the pyruvate decarboxylation occurs, producing acetyl CoA. This irreversible reaction traps the acetyl CoA within the mitochondria (the acetyl-CoA can only be transported out of the mitochondrial matrix under conditions of high oxaloacetate via the citrate shuttle, a TCA intermediate that is normally sparse). The carbon dioxide produced by this reaction is nonpolar and small, and can diffuse out of the mitochondria and out of the cell.
In prokaryotes, which have no mitochondria, this reaction is either carried out in the cytosol, or not at all.
Read more about this topic: Pyruvate Dehydrogenase Complex