Structure and Mechanism of Lactate Dehydrogenase

Abstract

The enzyme lactate dehydrogenase (LDH) catalyses the conversion of lactate to pyruvate in the presence of the coenzyme nicotinamide adenine dinucleotide (NAD). It is composed of four subunits each of molecular weight 35,000 (Appella and Markert, 1961; Cahn et al, 1962). The subunits are single polypeptide chains of either H (heart) or M (muscle) variety (Wieland and Pfleiderer, 1957; Markert and Møller, 1959). Hybridization of these chains gives rise to five possible isoenzymes per species. This paper concerns itself with the properties of the M₄ isoenzyme of dogfish (Squalus acanthius). Rossmann et al (1967) have previously reported that the apo-enzyme crystallizes in space group F422 with a = 146.9, c = 155.2A, and one polypeptide chain per asymmetric unit. Adams et al (1969) showed that the molecular center coincided with the intersection of a defined set of mutually perpendicular two-fold axes in the crystal lattice. They also reported a low resolution (5.0A) structure in which the boundaries of the molecule and subunits could be traced. In addition some properties of the binary coenzyme complex were discussed.

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