Lipid and polypeptide components of the crystalline yolk system from Xenopus laevis

The polypeptide and lipid components of the crystallinelipoprotein-phosphoprotein from the yolk system of Xenopus laevis are described. This lipoprotein complex contains 17% lipid of which 75% is phospholipid. The phospholipid fraction consists of mostly phosphatidylcholine and phosphatidylethanolamine. The neutral lipid fraction contains mainly triglyceride. The phosphoprotein, phosvitin, has been separated from the lipoprotein, lipovitellin, by classical methods. Three polypeptide chains can be observed in the lipoprotein and their molecular weights as determined by sodium dodecyl sulfate gel electrophoresis are 105,500, 35,500, and 32,000. Phosvitin behaves abnormally on these gels, but analysis of the results suggests Mr = approximately 16,000 to 19,000/polypeptide chain. The lipovitellin component of the yolk complex contains approximately 100 bound lipid molecules/dimer. The stoichiometry of the components of this crystalline lipoprotein system is discussed in terms of the results obtained in this study and those of other workers.