Caspartin and calprismin, two proteins of the shell calcitic prisms of the Mediterranean fan mussel Pinna nobilis.

We used the combination of preparative electrophoresis and immunological detection to isolate two new proteins from the shell calcitic prisms of Pinna nobilis, the Mediterranean fan mussel. The amino acid composition of these proteins was determined. Both proteins are soluble, intracrystalline, and acidic. The 38-kDa protein is glycosylated; the 17-kDa one is not. Ala, Asx, Thr, and Pro represent the dominant residues of the 38-kDa protein, named calprismin. An N-terminal sequence was obtained from calprismin. This sequence, which comprises a pattern of 4 cysteine residues, is not related to any known protein. The second protein, named caspartin, exhibits an unusual amino acid composition, …