The yolk platelets found in oocytes from the toad Xenopuslaevis have been studied by electron microscopy and X-ray diffraction in the first stages of a low-resolution structure determination. The crystalline nature of the platelet has been confirmed, and powder photographs of four forms of the lipoprotein-phosvitin complex have been indexed. The X-ray results from wet native crystals are most consistent with an orthorhombic lattice of unit cell dimensions a = 88·5 Å, b = 174·8 Å, and c = 198·9 Å. Nine different views of the lattice have been found in electron micrographs of fragments broken from the microcrystals and negatively stained with uranyl acetate. Optical diffraction patterns from these micrographs have been indexed in terms of the lattice derived from the X-ray diffraction results.
Bibliographical noteFunding Information:
The authors are grateful to C. Schutt and A. Jack for their help during the early stages of this work. We are also indebted to I). Taupin for use of his powder indexing program. We are grateful to the National Science Foundation for research funds (BMS74-03397) and for predoctoral support for one of us (I). H. O.) and to the National Institutes of Health (GM-13925 and CA-13202). And lastly we acknowledge the support for one of us (M. L. C.) by National Institutes of Health training grant (GM-02016).