How is pyruvate converted to lactate?

Pyruvate from glycolysis is converted to lactate by fermentation, using the enzyme lactate dehydrogenase and coenzyme NADH. This conversion occurs in three types of conditions: if the cell is not oxygenated, if a cell lacks a mitochondria, and if energy demand has increased to exceed the rate that oxidative phosphorylation can provide enough ATP. The process of fermentation results in the reduction of pyruvate to form lactic acid and the oxidation of NADH to form NAD+. This step allows glycolysis to continue through the glyceraldehyde-3-phosphate dehydrogenase reaction. Fermentation will replenish NAD+ from the NADH+ H+ produced in glycolysis in order to keep the glycolysis cycle going.