Fates of Pyruvate - 3. Lactic Acid Fermentation
KEY FATES OF PYRUVATE
1. Acetyl CoA: substrate for citric acid cycle and fatty acid synthesis
2. Oxaloacetate: intermediate in CAC and substrate for gluconeogenesis
3. Lactate: produced by eukaryotes in absence of oxygen
4. Ethanol: produced by yeast and some bacteria (including intestinal flora) in absence of oxygen.
- There are aerobic and anaerobic conditions.
Lactic acid fermentation (humans)
- Anaerobic conditions
- Occurs in exercising muscle and red blood cells: cytosol
- Glycolysis: 1 glucose = 2 pyruvates + 2 ATP + 2 NADH
- Lactate dehydrogenase: 2 pyruvate + 2NADH = 2 lactate + 2 NAD+
- Reversible reaction
- Lactate can enter bloodstream and travel to liver: lactate dehydrogenase catalyzes reverse reaction (lactate to pyruvate)
Clinical correlation: intense exercise can produce lactic acidosis; lactate accumulates in muscle cells and causes intracellular drop in pH