WATER-SOLUBLE CA-2+-CALMODULIN-BINDING PROTEINS IN EMBRYO OF THE SEA-URCHIN STRONGYLOCENTROTUS-INTERMEDIUS

1. About 0.3-0.4% of total water-soluble protein extracted from sea urchin embryos at the two-cell and early-gastrula stages was Ca2+-dependently bound to immobilized calmodulin. 2. SDS-PAGE of calmodulin-binding proteins revealed at least 20 polypeptides ranging from 200 to 15.5 kDa, and 70-80% of the protein belonged to a dozen major polypeptides. Polypeptides of 70, 55, 50,45 and 18 kDa seemed to be the same as those that were detected earlier (Iwasa and Mohri, J. Biochem. 94, 575-587, 1983). 3. The polypeptide spectrum of calmodulin target proteins changed significantly, e.g. the major polypeptides of 70 and 41 kDa increased, and the 200 and 43 kDa polypeptides decreased sharply during development from the two-cell to the early-gastrula stage. 4. According to our estimates, the molar concentrations of the calmodulin and targets were close enough, and therefore the Ca2+ signal should depend on the spatial-temporal distribution of free calmodulin in the cells.