PROTEINS OF MORULA-LIKE CELLS IN HEMOLYMPH OF THE GIANT CLAM, TRIDACNA-DERASA

The morula-like cell, a hemocyte packed with many large (about 3 mu m in diameter) electron-dense granules, is found only in the hemolymph o f giant clams belonging to the Tridacnidae. To clarify the function of the morula-like cell, we investigated its proteins, especially those found in the large granules. Proteins with molecular weights of 64 kDa , 17 kDa and 7.4 kDa were found to be specific to this type of hemocyt e. N-terminal amino acid sequence analysis revealed that the 17-kDa an d 7.4-kDa proteins were novel proteins rich in aromatic amino acids. R abbit polyclonal antibody against a synthetic peptide of the 7.4-kDa p rotein reacted not only with that protein but also with a larger molec ular weight (about 16-kDa) protein in the morula-like cell. Examinatio n of the N-terminal amino acid sequences showed that the 16-kDa protei n is distinct from the 17-kDa protein, and Western blot analysis sugge sted that it is a precursor of the 7.4-kDa protein. The zooxanthellate portion of clam mantle and kidney contained proteins immunoreactive t o the antibody, but the azooxanthellate portion of the mantle did not contain any immunoreactive protein. These results suggest that the mor ula-like cells interact with the zooxanthellae.