The lipid and polypeptide components of the crystalline lipoprotein complex comprising the yolk system of amphibians have been determined. All four polypeptide chains contained in this lipoprotein have been purified in order that lipid binding studies may eventually be done. In addition, the molecular weights and amino acid compositions of these protein components have been obtained. Some preliminary data on the molecular weights of the complex as determined by light scattering have been measured. These results suggest the presence of higher order aggregates if the complex has a nominal molecular weight of 500,000. Proposed studies include the determination of the light scattering data at high pH in order to determine the molecular weight of the monodisperse species of the lipoprotein complex. A preliminary map of the structure of the complex has been obtained by the method of three-dimensional image reconstruction. The proposed work will complete this study by using all available electron micrographs. Crystals of pig heart mitochondrial malate dehydrogenase has been obtained from solutions containing polyethylene glycol. Preliminary x-ray data will be obtained from these crystals and if the needle-like habit can be changed to a form slightly more suitable for x-ray data collection, a low resolution structural analysis will follow. BIBLIOGRAPHIC REFERENCE: Weininger, M., Birktoft, J.J. and Banaszak, L.J., "Conformation Changes and Non-Equivalence in the Binding of NAD ion to Cytoplasmic Malate Dehydrogenase" in Pyridine Nucleotide-Dependent Dehydrogenases, Verlag Walter de Gruyter, Publishers, Berlin, Germany (1977) in press.