KREBS CYCLE
The reaction chain of the third stage of catabolism is called Krebs cycle (citric acid cycle, tricarbonic acid cycle, tricarboxylic acid cycle). The cycle includes ten intervening stages. The starting substrate, and at the same time the ultimate substrate of this cycle is oxalacetic acid. As the result of the work of the Krebs cycle the carbonic acid, protons and electrons are produced. Protons remain in the matrix, and electrons arrive on the first element of the respiratory chain. All the enzymes of the Krebs cycle are in the matrix of mitochondria.