Alterations in the Proteins of Sea Urchin Egg Homogenates Treated With Calcium

The addition of Ca++ to homogenates of Arbacia eggs which have been previously made calcium-free results in the loss in solubility of certain protein constituents of the homogenate.2. The precipitated material is rich in nucleic acid, and comes, at least in part, from the fraction non-sedimentable at 2000 g.3. The addition of Ca++ to homogenates activates a proteolytic enzyme and leads to the release of small amounts of additional non-protein nitrogen.4. None of these reactions can be ascribed to the high ionic strength of solutions of calcium salts as compared with that of isosmotic solutions of uni-univalent salts.5. The fraction undergoing solubility loss appears to be electrophoretically homogeneous, since it is represented by the largest and slowest-migrating boundary in the water extract of the homogenate.6. Electron microscope observations reveal that the aggregating material consists of spherical or discoidal particles of (flattened) diameter 380 Å. The aggregation pattern observed is that of microflocs.7. The possible significance of these observations for the mechanism of the surface precipitation reaction and for sol-gel changes in the cell interior is discussed.