Lactate dehydrogenase (LDH) is an enzyme present in a wide variety of organisms, including plants and animals. It catalyses the interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD+. In medicine, LDH is often used as a marker of tissue breakdown as LDH is abundant in red blood cells and can function as a marker for hemolysis. In mammals, three types of LDH subunits (35 kDa) are encoded by the genes Ldh-A, Ldh-B, and Ldh-C. Lactate dehydrogenase B (LDH-B, heart subunit, LDH-H) is involved in the conversion of L-lactate and NAD to pryruvate and NADH and it is predominantly localized in the heart tissue. Similar to other LDH subunit, LDH-B is considered to be an important marker for germ cell tumor.

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