Isolation of a metal-binding protein from ovaries of dab (Limanda limanda L.) distinct from metallothionein: effect of cadmium exposure.

Metal-binding proteins were isolated from ovaries of dab (Limanda limanda L.) caught in the North Sea. Separation of the heat-treated cytosolic fraction of dab ovaries by gel-filtration chromatography revealed the presence of a major zinc-binding protein with a low-molecular-weight of 10,000-12,000 Da, similar to mammalian metallothionein (MT). The metal-binding protein was analyzed by anion-exchange chromatography and by reversedphase high-performance liquid chromatography. The metal-binding protein from dab ovaries consists of one major isoform. Zinc could be displaced from the isoform by a saturation of the extract with cadmium, leading to altered retention of the protein at the RP column. In a laboratory experiment, dabs were treated intraperitoneally with cadmium (0.5 and 1.5 mg/kg body wt). In contrast to hepatic dab MT, the metal-binding protein in ovaries was not inducable by cadmium; however, dose-dependent amounts of cadmium were bound to the ovarian protein after the metal exposure. The amino acid composition was different from that of mammalian MT. The results suggest that the metal-binding protein in dab ovaries is possibly involved in ovary development and can be affected by cadmium exposure.