The three-dimensional structure of porcine heart mitochondrial malate dehydrogenase at 3.0-A resolution

In a previous study, we reported the apparent similarity between a low resolution electron density map of mitochondrial malate dehydrogenase and a model of cytoplasmic malate dehydrogenase (Roderick, S. L., and Banaszak, L. J. (1983) J. Biol. Chem. 258, 11636-11642). We have since determined the polypeptide chain conformation and coenzyme binding site of crystalline porcine heart mitochondrial malate dehydrogenase by x-ray diffraction methods. The crystals from which the diffraction data was obtained contain four subunits of the enzyme arranged as a "dimer of dimers," resulting in a crystalline tetramer which possesses 222 molecular symmetry. The overall polypeptide chain conformation of the enzyme, the location of the coenzyme binding site, and the preliminary location of several catalytically important residues have confirmed the structural similarity of mitochondrial malate dehydrogenase to cytoplasmic malate dehydrogenase and lactate dehydrogenase.