Milchsäuredehydrogenase

Milchsäuredehydrogenase, often abbreviated as LDH or LD, is an enzyme found in the cytoplasm of all animal cells. Its primary function is to catalyze the reversible conversion of lactate to pyruvate, a key step in cellular respiration. In anaerobic conditions, when oxygen is scarce, cells rely on LDH to regenerate NAD+ from NADH, which is essential for glycolysis to continue producing ATP. This process allows cells to generate energy even without oxygen, albeit less efficiently than aerobic respiration.

LDH exists in several isoenzyme forms, each composed of different combinations of two subunits, H (heart) and M (muscle). These isoenzymes have slightly different kinetic properties and are expressed in varying amounts in different tissues. For example, LDH-1, primarily found in the heart and red blood cells, has a higher affinity for lactate. LDH-5, prevalent in the liver and skeletal muscle, is more active at higher pyruvate concentrations.

Measuring LDH levels in blood serum is a common diagnostic tool. Elevated LDH can indicate tissue damage or inflammation, as the enzyme is released into the bloodstream when cells are injured. Conditions such as myocardial infarction, liver disease, muscle injury, hemolytic anemia, and certain cancers can lead to increased serum LDH. However, due to its widespread presence in tissues, LDH is not specific to any single condition, and other tests are usually needed for a definitive diagnosis.