PRIMARY STRUCTURES OF 7 METALLOTHIONEINS FROM RABBIT-TISSUE

Metallothionein from tissues of rabbits exposed to cadmium chloride wa s separated into seven distinct isoforms by reverse-phase liquid chrom atography and their complete amino acid sequences were determined. Fiv e of the seven isometallothioneins showed structural features so far n ot identified in other mammalian metallothioneins. Thus, two isoprotei ns contain a polypeptide with a chain length of 62 rather than 61 amin o acid residues. Two isoforms are characterized by an additional posit ive charge and one by the presence of an isopeptide bond between aspar tic acid and serine in the N-terminal half of the protein. The isoprot eins characterized were identified from different sources: rabbit live r and kidney and a rabbit kidney cell-line (RK-13). In all three, the structural characteristics of the individual isoforms are retained, in dicating that in the different tissues the same mechanisms control the synthesis and the stability of the different cadmium-induced isoMTs.