An enzymatic comparison of sea urchin egg ghosts prepared before and after fertilization

Ghosts were prepared from sea urchin eggs, before and after fertilization. Eggs were treated with Mg++ to stabilize the surface. Cytoplasm was then released by osmotically lysing the cells and washing repeatedly at low ionic strength. Microscopically, the resultant ghosts appear to contain the extraneous surface coats, some cell cortex, and the plasma membrane, but relatively little cytoplasm. This appearance and the higher specific activities of Na+‐K+‐ATPase, Mg++‐ATPase, and acetylcholinesterase in ghosts than in whole egg homogenates, indicates the usefulness of ghost preparations as egg surfaces in enzyme comparison studies. The specific activities of five of the six enzymes measured are different when compared in ghosts prepared before and after fertilization. Glucose‐6‐phosphate‐dehydrogenase, acetylcholinesterase, and Na+‐K+‐ATPase activities are greater in fertilized than in unfertilized egg ghosts, whereas the Mg++‐ATPase and glucose‐6‐phosphatase activities are lower. The changes in enzyme specific activities following fertilization may be related to structural and functional changes which occur in the egg surface at that time.