PROPERTIES OF COD METALLOTHIONEIN, ITS PRESENCE IN DIFFERENT TISSUES AND EFFECTS OF CD AND ZN TREATMENT

One isoform of the low-molecular-weight metal-binding protein metallot hionein (MT) has been isolated from the liver of Atlantic cod by size- exclusion and ion-exchange chromatography. Cod MT contained 33% cystei ne, no aromatic amino acids or arginine. As is the case for other pisc ine MTs, the N-terminus of cod MT lacked the asparagine in position 4 which is present in mammalian MTs. In addition, cod MT differed from a ll other vertebrate MTs described in that the N-terminal methionine wa s not acetylated. Antibodies were raised in rabbits against hepatic MT from cod by repeated injections of native protein mixed with adjuvant . Anti-cod MT antisera cross reacted with similarly-sized proteins in liver, brain, anterior kidney, posterior kidney, spleen, intestine, gi lls and ovaries. The putative MT in cod brain migrated differently to that of the other tissues in native gel electrophoresis. Intraperitone ally injected Cd (1 mg/kg) was nearly entirely associated with the MT- peak in hepatic and renal cytosols, whereas a single injection of Zn ( 10 mg/kg) resulted in increases in all cytosolic Zn pools of the liver and no apparent change in cytosolic Zn, Cu, Ni or Cd in kidney.