Metal‐binding proteins in eggs of various sea urchin species.

Metallothionein presence and amount were determined in the unfertilized eggs of six sea urchin species by silver saturation assay and gel‐chromatography of cell extracts. The results showed high levels of metallothionein in the egg cytoplasm of the two Mediterranean species Paracentrotus lividus and Sphaerechinus granularis. No metallothionein was found either in the eggs of Arbacia lixula, or in those of the three Eastern species Strongylocentrotus intermedius, Temnopleurus hardwickii and Clypeaster japonicus. However, the extracts of the latter three species revealed the presence of zinc bound in a macromolecular form, thus suggesting the existence of metal‐binding proteins distinct from metallothioneins.