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