Isolation and partial characterization of a cadmium-binding protein from the liver of alligators exposed to cadmium.

Seven American alligators, Alligator mississippiensis, were each administered a single, intracardiac injection of cadmium chloride, at a dose of 1.0 mg Cd/kg body wt. At sacrifice, the highest concentration of Cd was found in the liver, bound to a cytosolic protein with characteristics similar to mammalian metallothionein (MT). Gel filtration (Sephadex G-75) of the cytosol revealed a peak containing Cd and to a lesser extent, zinc (Zn), having the same relative elution volume (Ve/Vo) as rat hepatic Cd, Zn-MT. Anion-exchange chromatography (DEAE-Sephacel) of material having a Ve/Vo of 1.7-1.9 revealed a major Cd-peak corresponding to rat Cd, Zn-MT(I) and a minor peak corresponding to Cd, Zn-MT(II). Neither peak contained significant amounts of Zn. Heat treatment of alligator hepatic cytosol, followed by selective acetone precipitation, yielded material having a molar Cd:Zn ratio of 9.15:1 compared to 0.67:1 in material purified from Cd-pretreated rat liver. Spectral analysis of the material purified from both sources showed an absorbance peak between 250 and 260 nm and no absorbance peak at 280 nm, characteristic of mammalian MT.