Pyruvate/Lactate/Ethanol Metabolism

Pyruvate is typically considered the last molecule produced in glycolysis. Under aerobic conditions pyruvate is transformed into acetyl-CoA, which then enters the citric acid cycle. Under anaerobic conditions, however, something else must be done to oxidize all the NADH formed in glycolysis.

> 1. In animal cells and lactic acid bacteria, pyruvate is converted to lactate. In this case, NADH adds electrons to pyruvate, forming NAD+ and lactate. The NAD+ can then catalyze reaction 6 of further glycolysis reactions. Lactate appears to be produced under aerobic cellular conditions as well, however, so the role of lactate formation is not completely clear.

> 2. Yeasts recycle NADH to NAD+ by alcoholic fermentation:

> Pyruvate ->acetaldehyde ->ethanol. The last step converts NADH to NAD+.

> The reduction of acetaldehyde to ethanol is coupled to the oxidation of NADH to NAD+.

See also: Lactate, Lactate Dehydrogenase