Purification and molecular properties of two cadmium-binding glycoproteins from the hepatopancreas of a whelk, Buccinum tenuissimum.

Two cytoplasmic cadmium-binding glycoproteins from the hepatopancreas of a whelk, Buccinum tenuissimum, were purified to homogeneity by Sephadex G-75 gel filtration and two DEAE-Sephadex A-25 chromatographies in the presence of 2-mercaptoethanol. These two cadmium-binding glycoproteins, termed FIIA and FIIB, each showed a single band after electrophoresis on 10% polyacrylamide gel at pH 8.9. The molecular weight of FIIA was estimated as 8000 and that of FIIB as 13000 by SDS-polyacrylamide gel electrophoresis. Based on molecular weights of 6500 and 11900 for the protein moiety of FIIA and FIIB, respectively, the total number of amino acid residues was 52 in the former and 94 in the latter. Three and two cysteine residues in FIIA and FIIB, respectively, were titratable with p-chloromercuribenzoate. FIIB also contained two more half-cystine residues. The sugar contents of FIIA and FIIB were about 20.5% and 8.7% by weight, respectively, consisting of galactose, mannose, fucose and amino sugar. The purified glycoproteins FIIA and FIIB contained about 0.6% and 1.0% cadmium by weight, respectively, and both showed strong metal-binding capacity, especially for cadmium, copper and mercury. The apparent cadmium dissociation constants for FIIA and FIIB after treatment with 2-mercaptoethanol were 7.3 X 10(-6) and 9.1 X 10(-7) M, respectively. Cadmium contents at saturation were nearly 6 and 8 gatom per mole for FIIA and FIIB, respectively.