Purification of the most abundant protein in the coelomic fluid of a sea urchin which immunologically cross reacts with 23S glycoprotein in the sea urchin eggs.

The most abundant glycoprotein in the coelomic fluid of sea urchin Anthocidaris crassispina was purified and its subunit structure, molecular form in the native state, amino acid composition, and electron micrographic image were studied. The results showed that the protein in its native state was basically a tetramer with a total molecular weight of about 700,000, which was in equilibrium with a high molecular weight form corresponding to an octamer. The electron micrograph of the tetramer showed two ellipsoidal units aligned in parallel with a wide gap in between. The subunits all had the same molecular weight of 180,000 +/- 10,000 and were disulfide bonded in pairs. The carbohydrate content was about 16% with mannose and fucose as the two most abundant sugars. Although this protein accounted for 70% of the total protein in the coelomic fluid, it did not take part in the known activities of the fluid, namely hemagglutination and coagulation. Despite its structural similarity to the mammalian alpha-2-macroglobulin or reptilian and avian ovomacroglobulins it did not interact with bovine trypsin or chymotrypsin. This protein showed immunological cross reactivity with 23S glycoprotein purified from sea urchin eggs which, we believe, corresponds to the previously described 22-27S protein particles in eggs.