A novel 15 kDa Ca2+-binding protein present in the eggs of the sea urchin, Hemicentrotus pulcherrimus.

Abstract A novel Ca 2+ -binding protein, different from calmodulin, has been purified to homogeneity from the soluble cytoplasmic protein fraction of the egg of the sea urchin, Hemicentrotus pulcherrimus . This protein, designated as 15 kDa protein, shows a Ca 2+ -dependent mobility shift upon SDS-gel electrophoresis and has Ca 2+ -binding ability. This protein did not resemble the sea urchin egg calmodulin in either molecular mass or amino acid composition. The 15 kDa protein could not activate cyclic adenosine 3',5'-monophosphate-dependent phosphodiesterase from bovine brain and did not bind to fluphenazine-Sepharose 6B. Antibodies against the 15 kDa protein did not react with sea urchin egg calmodulin. These results suggest that the 15 kDa protein is a novel Ca 2+ -binding protein in the sea urchin egg.