The Isolation and Characterization of a Cadmium and Zinc-binding Protein fromTetrahymena pyriformis

Abstract

A cadmium and zinc-binding protein similar to metallothionein has been isolated from Tetrahymena pyriformis exposed to cadmium chloride. This protein contained 32.4% half-cystine, 23.7% acidic amino acids and 10.1% lysine. The amino acid composition was similar to that of copper-thionein of yeast. The metal-binding protein of Tetrahymena pyriformis contained 3.7 g atom cadmium, 0.7 g atom zinc, and O.l g atom copper per mol, and shpwed the spectral characteristics of cadmium-thionein, i.e., a broad shoulder at 250 nm and low residual absorption at 280 nm. The molecular weight of this protein was determined to be 11,000 by gel filtration in 6 M guanidine hydrochloride, although it moved like a protein with a molecular weight of 30,000 on ordinary gel filtration.