Property of Cadmium-binding Protein in Chlorella ellipsoidea

Some properties of Cd-binding protein (Cd-BP) in chlorella cells (Chlorella ellipsoidea) were examined. The Cd-BP was isolated and purified from the 105000×g supernatant of chlorella cells grown in a medium containing CdCl2 (1 mg Cd/l) by gel filtration on Sephadex G-75 and Sephadex G-25 and by ion exchange chromatography on DEAE-Sephadex A-25. In the DEAE-Sephadex A-25 chromatography a high concentration (0.6 M) of NaCl was required for eluting the Cd-BP. The molecular weight of the Cd-BP was estimated as approximately 8500 by gel filtration on Sephadex G-75. The 50% dissociation of Cd from the Cd-BP was given at pH 3.6. Absorption intensity of Cd-BP at 250 nm decreased with Cd dissociation from Cd-BP by lowering pH. These results suggest that the property of Cd-BP in chlorella cells is similar to that of mammalian metallothioneins except that the Cd-BP showed highly anionic behavior on the ion exchange chromatography.