A further substrate level phosphorylation occurs at the succinyl-CoA-synthase reaction. Thus two molecules of pyruvate (equivalent to one glucose) moving through the citric acid cycle generate 30 molecules of ATP. Two molecules of ATP are produced during glycolysis giving a total of 32. If the pyruvate is completely oxidized to carbon dioxide, the two molecules of NADH that are produced during glycolysis can also be asource of ATP. This NADH molecule is cytoplasmic and not mitochondrial, and in order to be able to generate ATP the electrons must be transported to the mitochondria. Depending on the transportation mechanism that is utilized, two or three ATP molecules can be obtained for each NADH molecule that is oxidized. So, a single glucose molecule, when it is fully respired, will generate between 35 and 37 molecules ATP in total, of which 33 to 35 are from the oxidative phosphorylation and two from substrate level phosphorylation (Rib´ereau-Gayon et al., 2000h). The energy yield from the yeast metabolism is therefore around 15 times higher for aerobic sugar metabolism in comparison with anaerobic sugar metabolism.