Natural occurrence of metallothioneinlike proteins in liver tissues of four fish species from the northeast Mediterranean Sea.

Fish with different ecological needs were captured from the northeast Mediterranean Sea to determine metallothioneinlike proteins in their livers. Heat-treated liver samples were run on a column packed with Sephadex G-75 (Sigma, Germany) for subsequent determination of metals, sulfhydryl, and absorbance at 254 and 280 nm. Liver cytosols of Sparus auratus and Mullus barbatus had three heat-stable protein peaks, whereas Mugil cephalus and Atherina hepsetus had two. The third protein peak, containing metallothionein-like proteins (5000 to 6000 Da), was present in all fish. Only high- and low-molecular-weight proteins contained sulfhydryl and metals. Zinc was the most abundant metal in the metallothioneinlike proteins, whereas cadmium and lead were not detected. The differences in the characteristics of metal-binding proteins among fish indicate that the biological characteristics of fish species should be carefully taken into account concerning natural monitoring studies.