Final answer:
LDH exists in five tetrameric isoenzyme forms in vertebrates, named LDH-A, LDH-B, and LDH-C, each with different physical characteristics and roles in tissues such as cardiac and skeletal muscles. LDH-C is considered the most recent evolutionary form in vertebrates.
Step-by-step explanation:
In vertebrates, lactate dehydrogenase (LDH) exists in five isoenzyme forms, which differ in physical characteristics such as molecular weight, charge, and affinity for substrates. LDH is a tetramer, which means it is composed of four polypeptide chains, and these can be in different combinations of H and M chains. The forms of LDH named LDH-A, LDH-B, and LDH-C are all synthesized in vertebrates, where the LDH1 (or H4) isoenzyme is predominantly present in cardiac muscle, and the LDH5 (or M4) isoenzyme is more abundant in skeletal muscle. Among these, LDH-C is suggested to be the most recently evolved form of the enzyme in both African frogs and humans, based on genetic relatedness studies.