lactate dehydrogenase
Summary
Lactate dehydrogenase (LDH) is a cytosolic enzyme found in nearly all body tissues that catalyzes the interconversion of pyruvate and lactate, using NADH/NAD+ as cofactors. It is a nonspecific marker of cellular injury or tissue breakdown, elevated in conditions like hemolysis, tissue infarction, and malignancy. LDH isoenzyme patterns can help localize the tissue of origin.
Detail
LDH catalyzes the reversible reaction: pyruvate + NADH ↔ lactate + NAD+, playing a key role in anaerobic glycolysis by regenerating NAD+ needed for glycolysis to continue when oxygen is limited. It exists as a tetramer of two subunit types (H and M), forming 5 isoenzymes (LDH-1 to LDH-5) with tissue-specific distributions: LDH-1 (heart, RBCs), LDH-2 (reticuloendothelial system), LDH-3 (lungs), LDH-4 (kidney, pancreas, placenta), LDH-5 (liver, skeletal muscle). Clinically, total serum LDH is a nonspecific but sensitive marker of cell death/tissue damage. Elevated LDH is seen in: hemolytic anemia (intravascular hemolysis releases LDH from RBCs), myocardial infarction (historically LDH-1 > LDH-2
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
- Harrison's Principles of Internal Medicine
- Kaplan USMLE Step 1 Biochemistry
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