The isomerization prepares the molecule for an oxidative decarboxylation in the next step of the cycle. In another complex reaction, a second oxidative decarboxylation occurs. The coenzyme A is removed, and enough energy is released to allow a substrate level phosphorylation. The 4-carbon succinate continues in the Krebs cycle, while the coenzyme A and the GDP are recycled. The remaining 4-carbon compound is fumarate.
Water is added to the fumarate to produce malate, in preparation for the last step of the cycle.
The cycle has been completed, and is ready to begin again. One ATP molecule was produced through substrate level phosphorylation during the Krebs cycle. Two carbon dioxide molecules were released. If the two ATP from the glycolytic pathway are added, this makes a total of 4 ATP recovered at the end of the Krebs cycle. Although this is better than the recovery of glycolysis alone, it is still inefficient.