Larval storage protein of the barnacle, Balanus amphitrite: biochemical and immunological similarities to vitellin.

Biochemical and immunological characterization of cyprid major protein (CMP), the principal protein constituent of cypris larvae of the barnacle Balanus amphitrite (Crustacea: Cirripedia), revealed similarities to egg-yolk protein, vitellin, as follows: CMP and vitellin heavy chain both have a molecular weight of 170 kDa by polyacrylamide gel electrophoresis containing sodium dodecylsulfate; CMP was crossreactive with antiserum against vitellin heavy chain in immunoblot analysis. The sequence of 11 amino acids in the amino-terminus of CMP, however, is not perfectly homologous to that of vitellin heavy chain. Thus, it was deduced that CMP was an isoform of vitellin. Concentration of CMP abruptly increased during the latter naupliar stages, reaching a peak just after metamorphosis to the non-feeding cypris stage, and decreased thereafter with aging of cyprids or during the early juvenile period. Specifically, the concentration of CMP in newly metamorphosed juveniles within one day decreased to 20% that of cyprids. CMP, therefore, appears to function as a storage protein during settlement of cyprids as well as metamorphosis to juveniles. Immunohistochemical analysis using antiserum against vitellin heavy chain on sectioned cyprids suggested that CMP is accumulated in the haemocoel.