Cori cycle

The Cori cycle (also known as the Lactic acid cycle), named after its discoverers, Carl Ferdinand Cori and Gerty Cori, refers to the metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is metabolized back to lactate.

Muscular activity requires ATP, which is provided by the breakdown of glycogen in the skeletal muscles. The breakdown of glycogen, a process known as glycogenolysis, releases glucose in the form of glucose-1-phosphate (G-1-P). The G-1-P is converted to G-6-P by the enzyme phosphoglucomutase. G-6-P is readily fed into glycolysis, (or can go into the pentose phosphate pathway if G-6-P concentration is high) a process that provides ATP to the muscle cells as an energy source. During muscular activity, the store of ATP needs to be constantly replenished. When the supply of oxygen is sufficient, this energy comes from feeding pyruvate, one product of glycolysis, into the Krebs cycle.

When oxygen supply is insufficient, typically during intense muscular activity, energy must be released through anaerobic metabolism. Lactic acid fermentation converts pyruvate to lactate by lactate dehydrogenase. Most important, fermentation regenerates NAD⁺, maintaining the NAD⁺ concentration so that additional glycolysis reactions can occur. The fermentation step oxidizes the NADH produced by glycolysis back to NAD⁺, transferring two electrons from NADH to reduce pyruvate into lactate. Refer to the main articles on glycolysis and fermentation for the details.

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