Isolation and characterization of metallothionein from the tortoise Clemmys mutica

A relatively high concentration of metallothionein was present in the liver of the control mature tortoise Clemmys mutica. The administrations of cadmium and copper to Clemmys mutica increased the metals in the liver with concomitant decrease of zinc, which was due to substitution of zinc in the native metallothionein with cadmium and copper. The Clemmys metallothionein was a mixture of three isoproteins which were abundant in half-cystine (34.2-34.6 mol%) and lysine (10.8-11.9 mol%), but lacked aromatic amino acids. One of the isoproteins, MT-I, contained one residue of histidine, which was an identical feature with frog and avian metallothioneins.