SEPARATION OF INTACT CORTICAL GRANULES FROM HOMOGENATE OF UNFERTILIZED SEA URCHIN EGGS BY ZONAL CENTRIFUGATION

Cortical granules are localized in the peripheral cytoplasm of mature, unfertilized eggs. The rupture of these granules constitutes one of the initial morphologically observable responses of the egg to fertilization or parthenogenetic activation. These organelles were separated from homogenates of unfertilized sea urchin eggs ( Strongylocentrotus purpuratus) by fractionation in the A-XII zonal centrifuge using sucrose density gradients constructed in (0.5 M) KCl. Cortical granules were abundant in electron micrographs of the most rapidly sedimenting population of particles. This population was rich in acid nitrophenylphosphatase activity, contained particles which stained metachromatically with toluidine blue and also contained yolk platelets. Acid phosphatase activity was also associated with several populations of slower sedimenting particles. Yolk platelets were widely distributed in the gradient, and were found in all fractions examined. The mitochondria and cytochrome oxidase activity were sedimented a short distance from the starting boundary.