Lactate Dehydrogenase (LDH)

Lactate dehydrogenases exist in four distinct enzyme classes. Two of them are cytochrome c-dependent enzymes with each acting on either D-lactate (EC 1.1.2.4) or L-lactate (EC 1.1.2.3). The other two are NAD(P)- dependent enzymes with each acting on either D-lactate (EC 1.1.1.28) or L-lactate (EC 1.1.1.27). This article is about the NAD(P)- dependent L-lactate dehydrogenase. The five isozymes that are usually described in the literature each contain four subunits. The major isozymes of skeletal muscle and liver, M₄, has four muscle (M) subunits; while H₄ is the main isozymes for heart muscle in most species, containing four heart (H) subunits. The other variants contain both types of subunits.Usually LDH-2 is the predominant form in the serum. A LDH-1 level higher than the LDH-2 level , suggests myocardial infarction. The use of this phenomenon to diagnose infarction has been largely superseded by the use of Troponin I or T measurement.