The citric acid cycle is the central oxidative pathway for biological organisms to produce atp under aerobic conditions. the cycle has several intermediates that it shares with the metabolism of proteins, fats, as well as carbohydrates. the enzymes used in each step of the pathway are often named after the type of reaction and either the product formed or the substrate acted upon. for example, oxidation and decarboxylation of the substrate isocitrate to form α-ketoglutarate is conducted by isocitrate dehydrogenase. isocitrate is the substrate and the reaction involves the transfer of a hydride, h−, to an electron acceptor. one enzyme of the citric acid cycle that does not utilize such a naming practice is aconitase, sometimes called aconitate hydratase. this enzyme catalyses isomerizations of citric acid substrates. put the enzymes of the first half of the citric acid cycle in order from left to right.