CHANGE OF LIPOVITELLIN DURING IN-VITRO OOCYTE MATURATION IN JAPANESE FLOUNDER PARALICHTHYS-OLIVACEUS

The change in molecular weight in the native form of lipovitellin during in vitro oocyte maturation was examined by gel chromatography in Japanese flounder, Paralichthys olivaceus, a marine teleost which lays pelagic eggs. The major protein peak at 400 kDa in the gel chromatogram of post-vitellogenic oocyte homogenate disappeared, and a new 140 kDa peak was observed in ovulated eggs. Both 400 kDa and 140 kDa yolk proteins were immuno-reactable to the specific antiserum against female specific-serum protein, suggesting that the 400 kDa yolk protein was lipovitellin of this species and the 140 kDa one was a proteolytic derivative from the 400 kDa lipovitellin. The time course analysis of the proteolysis of the lipovitellin during in vitro maturation demonstrated that the lipovitellin of 400 kDa was cleaved into 140 kDa during the later half of oocyte maturation. In combination with the result of SDS-PAGE analysis, this seems to be caused by the proteolytic cut-off of the 108 kDa peptide which constructs 400 kDa lipovitellin.