摘要：The induction of Cd-binding proteins were recognized in liver and kidney of ayu-fish, rainbow trout and catfish injected with CdCl2. One protein from ayu-fish, two isoproteins from rainbow trout and three isoproteins from catfish were separated as liver Cd-binding proteins by ion exchange chromatography with DEAE Sephadex A-25. These Cd-binding protein of ayu-fish and catfish were purified by rechromatography with Bio gel P-10. All of these purified fractions have much cadmium, a little copper and high absorption at 254 nm. By the analysis of amino acid compositions, each protein has high cysteic contents and absence of aromatic amino acids and histidine. These proteins were identified as (Cd, Cu)-metallothionein, and the isoproteins in catfish named MT-I, MT-II and MT-III. Some researchers presented the theory that the isometallothioneins was induced as more efficient physiological function in the evolution. The authors thought that catfish, α-mesosaprobic organismus, gained duplication of the metallothionein gene, and that the metallothionein acted more reasonable detoxification in polluted water area. Ayu-fish, oligosaprobic organismus, has not duplication of the metallothionein gene. Metal-binding proteins were found in livers of non-injected catfish, rainbow trout and ayu-fish. These metal compositions were zinc and copper and it was suggested that these proteins were (Zn, Cu)-metallothioneins.
