Cytoplasmic malate dehydrogenase—Heavy atom derivatives and low resolution structure

Abstract

The structure of the cytoplasmic form of malate dehydrogenase from pig heart has been determined at low resolution (5 Å), using single crystal X-ray diffraction methods. The malate dehydrogenase crystals contain the dimeric molecule of molecular weight 72,000 in the asymmetric unit. Phases for the diffraction data were obtained using isomorphous heavy atom methods. Three types of heavy atom compounds were used; they include a mercurial derivative, platinum compounds and the uranyl ion. The diffraction data were collected by diffractometry using a graphite crystal monochromatized X-ray source. The data were measured by using a partial omega scan and correcting for background scattering from a predetermined table. The low-resolution electron density map clearly indicated the molecular envelope. The over-all dimensions of the malate dehydrogenase in terms of some net spheroidal shape is 64 Å × 64 Å × 45 Å. This structure is roughly subdivided into two subunits. Examination of a model of this density indicated that the two subunits are related by approximate 2-fold rotational symmetry.