COMPLETE AMINO-ACID-SEQUENCES OF 5 DIMERIC AND 4 MONOMERIC FORMS OF METALLOTHIONEIN FROM THE EDIBLE MUSSEL MYTILUS-EDULIS

Cadmium-induced metallothioneins from the common sea mussel, Mytilus e dulis, were shown to comprise of two groups of isoforms having apparen t molecular masses of 10 kDa and 20 kDa. The 10-kDa group was resolved by anion-exchange chromatography into four fractions while the 20-kDa group was resolved into three fractions using this method. After meta l removal and S-methylation of the cysteine residues using methyl-p-ni trobenzenesulphonate the complete amino acid sequences were determined . Five isoforms of the 20-kDa group were shown to possess monomeric un its consisting of 71 amino acids. These proteins were distinct from th e four 72-amino-acid proteins of the 10-kDa group. The FASTA algorithm has been used to compare the degree of similarity between the mussel metallothionein MT-10-IV isoform and other metallothioneins. The musse l MT-10-IV isoform exhibited substantial similarity to other molluscan metallothioneins. Moreover, the mussel metallothionein exhibited more similarity to vertebrate metallothioneins than to those of non-mollus can invertebrates, thus suggesting that the mussel metallothioneins ar e class I metallothioneins.