In eukaryotes, pyruvate is transported into the mitochondrial matrix (see Figure 5.11), where the next step in the aerobic catabolism of glucose occurs. This step involves the oxidation of pyruvate to a two-carbon acetate molecule and CO₂. The acetate is then bound to coenzyme A to form acetyl coenzyme A (acetyl CoA); CoA is used in various biochemical reactions as a carrier of the acetyl group (H₃C—C=O).

Pyruvate is the link between glycolysis and further oxidative reactions (see Figure 9.4).

The formation of acetyl CoA is a multistep reaction catalyzed by the pyruvate dehydrogenase complex, which contains 60 individual proteins and 5 different coenzymes. The overall reaction is exergonic, in which one molecule of NAD⁺ is reduced to NADH. However, the main role of acetyl CoA is to donate its acetyl group to the four-carbon compound oxaloacetate, forming the six-carbon molecule citrate. This initiates the citric acid cycle, one of life’s most important energy-harvesting pathways.