NADH molecules are produced during the citric acid cycle, or Krebs cycle, from the reduction of the NAD+ molecules. NAD+ molecules can be reduced in three different stages of the cycle. From isocitrate to α-ketoglutarato, one NAD+ receives an H+ and it becomes NADH. The same process happens again with other NAD+ molecules when from α-ketoglutarato to succinyl CoA, and when from malate to oxaloacetate.
