Structural Constraints of Possible Mechanisms of Lactate Dehydrogenase as Shown by High Resolution Studies of the Apoenzyme and a Variety of Enzyme Complexes

In vertebrates, the NAD+-dependent enzyme lactate dehydrogenase (LDH) (EC 1.1.1.27) is a tetramer (mol wt 140,000) which catalyzes the interconversion of l(+) lactate and pyruvate. Two subunit types predominate, the M type in skeletal muscle and the H type in heart tissue. The subject of this study is the M4 isoenzyme from dogfish (Squalus acanthius).