Physico-chemical properties of lactic dehydrogenase.

Although the mechanism of the enzymatic reaction catalyzed by lactic dehydrogenase has been investigated by several workers, little work has been reported on the physical chemistry of this protein. In particular, a precise value for the molecular weight has not been reported. Meister (1) has estimated the molecular weight to be of the order of 100,000 to 150,000. Neilands (2) has reported a value of 135,000 to 150,000. In previous reports from this laboratory (3) the number of moles of coenzyme bound per mole of protein, with 135,000 as the molecular weight of the protein, has been found to be approximately 3.6. From similar measurements which yielded the same nonintegral ratio of moles bound per mole protein, Velick (4) has suggested that the correct molecular weight is 150,000. The present paper presents results of measurements which suggest that beef heart lactic dehydrogenase has a molecular weight of approximately 72,000 and that the protein associates in solution as protein concentration is increased.