The Fates of Pyruvate
 
As mentioned in the previous blog, obligatory glycolytic cells lack the apparatus (eg, mitochondria) to fully oxidize fuels down to CO2 and water. Thus, they can't run on fatty acids, ketones, or beta-hydroxybutyrate. During prolonged starvation, there's always some glucose in the blood, so they survive.

Recommended textbook: Stipanuk or Gropper.

Glucose -> glycolysis -> pyruvate: then to lactate or the mitochondria, depending on the context. Skeletal muscle has mitochondria, but if you're exercising hard, glycogen to lactate produces more energy faster than glycogen to pyruvate to mitochondria. Blood lactate increases in this context. During prolonged starvation, lactate is a valuable precursor for gluconeogenesis, so many tissues release lactate instead of oxidizing pyruvate.

 

"In obligatory glycolytic tissues, the end product of pyruvate is lactate. This enters the blood stream and can be reconverted to glucose in the liver. In some tissues much of the pyruvate may also be converted to alanine via transamination, again this is taken up by the liver and used to make glucose." Glucose is kind of important around here.

Lactate, pyruvate, and alanine considered as a unified triad, the concentration of each is very dependent on the concentrations of the other two. Lactate, pyruvate, and alanine are essentially in equilibrium. Some tissues such as brain, heart, and kidney can utilize lactate as a fuel, they simply convert it to pyruvate and oxidize in mitochondria.  

In the mitochondria, pyruvate is converted to acetyl-CoA and CO2. THIS IS HIGHLY IMPORTANT because it represents a permanent loss of precious glucose/gluconeogenic precursor. Once that CO2 is stripped away, we can't put it back on! This is also relevant for "refeeds" TO BE CONTINUED

That's all for now!

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