The isolation and characterization of a cadmium and zinc-binding protein from Tetrahymena 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 0.1 g atom copper per mol, and showed 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 6m guanidine hydrochloride, although it moved like a protein with a molecular weight of 30, 000 on ordinary gel filtration.