Identification and partial characterization of vitellin from the barnacle Balanus amphitrite

The major protein in occytes of the barnacle Balanus amphitrite has been identified as vitellin (Vt) and its biochemical properties partially characterized. SDS-PAGE of protein extracts from different developmental stages of occytes and embryos of B. amphitrite revealed that a 170 kDa polypeptide was abundantly present in fully matured oocytes. Its amount increased with occyte maturation and decreased with embryonic development after fertilization. Antiserum, prepared against 170 kDa polypeptide, was found to recognize only 170 kDa among proteins in ovary extract (OE) by immunoblot analysis. Immunohistochemical study indicated localization of 170 kDa polypeptide in yolk granules of oocytes, oviducts and embryos. Combination of native electrophoresis with agarose gel and SDS-PAGE displayed that the main protein in OE was lipophilic, contained 85 kDa polypeptide in addition of 170 kDa, and was positive in PAS reaction. The main peak eluted from OE contained 170 kDa and 85 kDa polypeptides, and corresponded to 200 kDa when filtrated through superose 6 gel. Conclusively, vitellin of B. amphitrite is a lipophilic glycoprotein consisting of two subunits, a heavy chain with 170 kDa and a light chain with 85 kDa. Two other barnacles, Megabalanus rosa and Tetraclita squamosa japonica, also contained proteins similar to B. amphitrite Vt.