pyruvate oxidation
/ py-ROO-vate ox-ih-DAY-shuhn /
Between two big stages of a journey there is often a short transfer step, like the walk from the train platform to the bus stop. In breaking down sugar, glycolysis ends in the cytosol but the next major stage happens deep inside the mitochondrion. Pyruvate oxidation is the brief transfer step that connects them.
After glycolysis, each pyruvate molecule is carried into the mitochondrion, where a complex of enzymes does three things to it. It snips off one carbon as carbon dioxide (the first CO2 you will exhale from this glucose), it strips off electrons and loads them onto NAD+ to make NADH, and it attaches the remaining two-carbon piece to a carrier molecule called coenzyme A, forming acetyl-CoA. Because each glucose gave two pyruvate, this step runs twice per glucose, yielding two CO2, two NADH, and two acetyl-CoA.
Pyruvate oxidation is short but pivotal: acetyl-CoA is the actual fuel that feeds the citric acid cycle, and it is also where the breakdown of fats and some proteins joins the same pathway. It is sometimes overlooked as a mere "link reaction," but it is the committed gateway into the oxygen-using heart of respiration, and the point of no return for that glucose.
The two pyruvate from one glucose enter the mitochondrion and are each converted to acetyl-CoA, releasing two molecules of CO2 — part of the carbon dioxide you breathe out.
Pyruvate oxidation turns pyruvate into acetyl-CoA, the fuel for the next stage.
This step requires oxygen indirectly: it only proceeds steadily when the later oxygen-using stages keep regenerating NAD+. It is not part of glycolysis, despite being sandwiched between it and the Krebs cycle.