Fates of pyruvate:
- Entry into the citric acid cycle. The Glycolysis releases associatively little of the energy present in a glucose molecule; much more is released through the subsequent operation of the oxidative phosphorylation and citric acid cycle.
Following this route under aerobic conditions and pyruvate is converted to acetyl CoA through the enzyme pyruvate dehydrogenase and the acetyl CoA then enters the citric acid cycle. A pyruvate dehydrogenase reaction is an oxidative decarboxylation:
![780_Fates of pyruvate.png](https://www.expertsmind.com/CMSImages/780_Fates%20of%20pyruvate.png)
- Conversion to fatty acid or ketone bodies. When the cellular energy stage is high (ATP in excess), the rate of the citric acid cycle decreases and acetyl CoA starts to accumulate. Under these conditions the acetyl CoA can be used of ketone bodies for fatty acid synthesis or the synthesis.
- Conversion to lactate. The NAD+ used during glycolysis (in the formation of 1, 3-bisphosphoglycerate through glyceraldehyde 3-phosphate dehydrogenase) must be regenerated if glycolysis is to continue. Under aerobic conditions NAD+ is reproduce through the reoxidation of NADH through the electron transport chain. When oxygen is limiting, as in muscle during vigorous contraction, the reoxidation of NADH to NAD+ through the electron transport chain becomes insufficient to maintain glycolysis. Under these conditions, NAD+ is reproducing alternativaly through conversion of the pyruvate to lactate through lactate dehydrogenase:
![1574_Fates of pyruvate1.png](https://www.expertsmind.com/CMSImages/1574_Fates%20of%20pyruvate1.png)
When sufficient oxygen becomes available once more, NAD+ levels rise by operation of the electron transport chain. Lactate dehydrogenase reaction then reverses to regenerate pyruvate which is converted through pyruvate dehydrogenase to acetyl CoA that can enter the citric acid cycle. Therefore the operation of lactate dehydrogenase in mammals is a mechanism for the reoxidation of NADH to NAD+ while permitting glycolysis to continue and ATP to be create under anaerobic conditions. The process is even more difficult in the case of vigorously contracting skeletal muscle. Now the lactate produced is transported in the bloodstream to the liver where it is converted back to glucose and can return once again through the bloodstream to the skeletal muscle to be metabolized to yield energy. At last, in some microorganisms and lactate is the normal product from pyruvate.
- Conversion to ethanol. In yeast and some other microorganisms under anaerobic conditions, the NAD+ needs for the continuation of glycolysis are regenerated through a procedure known as alcoholic fermentation. The pyruvate is translated to acetaldehyde (through pyruvate decarboxylase) and then to ethanol (through alcohol dehydrogenase) and latter reaction reoxidizing the NADH to NAD+ :
![1890_Fates of pyruvate2.png](https://www.expertsmind.com/CMSImages/1890_Fates%20of%20pyruvate2.png)