RESPONSES OF TETRAHYMENA PYRIFORMIS TO CADMIUM EXPOSURE-WITH SPECIAL REFERENCE TO A METALLOTHIONEIN-LIKE PROTEIN

Abstract

A metallothionein-like protein was identified from a mono-cellular organism Tetra-hymena pyriformis after incubation of organisms in the medium containing cadmium. Sulfhydryl group (SH) contents in the fractionated metallothionein-like protein in-creased up to twenty-four times of the control after exposure to cadmium. The increase of the protein was significantly correlated with the cadmium concentration in the medium (0.97). Molecular weight of the protein was estimated to be 59, 000 by sodium dodecyl sulfate gel electrophoresis and incorporation of ³⁵S-cysteine into the protein. Zinc or calcium added in the medium showed no effect on the amounts of metallothionein-like proteins induced by cadmium exposure. Increase of SH group content as a biological response to the cadmium exposure might be a common phenomenon observed in a variety of animal species.