1. It is an enzyme which catalyzes the reactionLactate ?? Pyruvate 2. This reaction helps the re-oxidation of NADH, H into NAD 3. It has 5 isoenzymes: LD1, LD2, LD3, LD4 and LD5.4. Medical importance:5. Estimation of the activity of lactate dehydrogenase enzyme helps in the diagnosis of heart and liver diseases:a) LD1: Elevated in some heart diseases e.g. myocardial infraction.b) LD5: Elevated in some liver diseases as acute viral hepatitis. .