What is lactate dehydrogenase (LDH)?

By William Aird

Lactate dehydrogenase (LDH) is a ubiquitous enzyme that catalyzes the conversion of lactate to pyruvate and back, resulting in conversion of NAD⁺ to NADH and back. LDH exists in five distinct forms, named LDH-1 through LDH-5, each having differential expression in different tissues:

  • LDH-1 is found primarily in heart muscle.
  • LDH-2 is the major isozyme of the reticuloendothelial system and red blood cells.
  • LDH-3 is highest in the lung.
  • LDH-4 is highest in the kidney, placenta, and pancreas.
  • LDH-5 is highest in the liver and skeletal muscle.
The red cell is a “fermenter“. It generates all of its energy from glycolysis without use of the Krebs cycle, yielding 2 molecules of ATP for very molecule of glucose. Instead of entering the Krebs cycle in the mitochondria (red cells do not have any mitochondria), pyruvate is metabolized to lactate via LDH.