The link reaction, also called pyruvate oxidation or oxidative decarboxylation of pyruvate, is a key metabolic step that connects glycolysis with the citric acid cycle. It prepares the product of glycolysis, pyruvate, for further oxidation by converting it into acetyl-CoA, a molecule that can enter the next stage of aerobic respiration.

In eukaryotes, this reaction takes place in the mitochondrial matrix, where the enzymes involved are organized into the pyruvate dehydrogenase complex. In prokaryotes, which do not have mitochondria, similar reactions occur in the cytoplasm. The location matters because the link reaction sits at the intersection of energy production and cellular organization.

What happens in the reaction

During the process, one carbon atom is removed from pyruvate and released as carbon dioxide. At the same time, the remaining two-carbon fragment is oxidized and attached to coenzyme A, forming acetyl-CoA. This step also reduces NAD+ to NADH, storing a small amount of energy in a usable electron carrier. In simplified form, the overall change is often written as: pyruvate + CoA + NAD+ → acetyl-CoA + CO2 + NADH.

Why it matters

The link reaction is essential because acetyl-CoA is the entry molecule for the citric acid cycle. Without it, carbohydrate breakdown would stop after glycolysis, and cells would lose a major route for extracting energy from food. The reaction is also important because it is generally irreversible under normal conditions, making it a committed step that channels carbon from pyruvate into aerobic metabolism.

  • Bridge function: connects glycolysis to the citric acid cycle.
  • Products: acetyl-CoA, carbon dioxide, and NADH.
  • Location: mitochondrial matrix in eukaryotes; cytoplasm in prokaryotes.
  • Enzyme system: carried out by the pyruvate dehydrogenase complex.

Because it links two major stages of respiration, the link reaction is often taught as one of the central control points in cellular metabolism. It shows how cells convert the end product of sugar breakdown into a form that can be used to make more energy, while also producing the reducing power needed for later steps of respiration.