ADP-ribosyl transferase activity of cholera toxin polypeptide A1 and the effect of limited trypsinolysis

Cd-binding peptide 1 (Cd-BP1) from $\text{S.}\text{pombe}$ (1) has been purified and characterized. Cd-BP1 has a characteristic shoulder at 265 nm in UV absorption spectrum, and shows two marked Cotton bands at 257 nm (negative) and 275 nm (positive). These are not found in the other Cd-thioneins (2) and are unique properties of Cd-BP1 from $\text{S.}\text{pombe}$. With acidification (pH 2) and successive neutralization, a shoulder at 265 nm in UV spectrum and a Cotton band at 275 nm disappeared, and the molecular weight changed from 4 000 to 1 800. In connection with these changes, two molecular forms of Cd-binding peptide are considered.