| Abstrakt: |
Following studies on calcium transport by isolated smooth endoplasmic reticulum from unfertilized sea urchin eggs (Oberdorf, J. A., Head, J. F., and Kaminer, B. (1986) J. Cell Biol. 102, 2205-2210) we have purified and partially characterized a calsequestrin-like protein from this organelle isolated from eggs from Strongylocentrotus droebachiensis and Arbacia punctulata. Muscle calsequestrin from sarcoplasmic reticulum is well characterized as a calcium storage protein. The egg protein resembles calsequestrin in its behavior in purification steps, electrophoretic mobility, blue staining with Stains-all on polyacrylamide gels, and its calcium binding and amino acid composition. Purification was attained with DEAE-cellulose and hydroxyapatite chromatography. The egg protein Mr of 58,000 in the Laemmli gel system is reduced to 54,000 under Weber-Osborn (neutral) conditions, thus showing a pH dependence in its mobility, although less than occurs with muscle calsequestrins. 25% of its amino acids are acidic and 10% basic. It binds 309 nmol of Ca2+/mg of protein, within the range reported for cardiac calsequestrin. Antigenically, the sea urchin egg protein is related to cardiac calsequestrin capable of binding anti-cardiac calsequestrin antibody. |
