Cadmium-binding proteins of three marine molluscs and characterization of two cadmium-binding glycoproteins from the hepatopancreas of a whelk, Buccinum tenuissimum.

Abstract

The cadmium-binding proteins were shown to exist in the hepatopancreas of three molluscs, a whelk, Buccinum tenuissimum, a turbo, Batillus cornutus, and a squid, Todarodes pacificus. Cadmium was efficiently accumulated in nature to a mean concentration of 119, 33, and 50 micrograms/g wet tissue in the hepatopancreas of three species of molluscs, and 30%, 11%, and 43% of the element in each tissue of whelk, turbo, and squid was extracted to the soluble fraction, respectively. Separation of the soluble fraction by Sephadex G-75 in the presence of 2-mercaptoethanol revealed that cadmium was mainly bound to the protein fraction FII of molecular weight 10,000. Two cytoplasmic cadmium-binding glycoproteins from the hepatopancreas of Buccinum tenuissimum were purified to homogeneity by Sephadex G-75 gel filtration and double DEAE-Sephadex A-25 chromatographies in the presence of 2-mercaptoethanol. These two cadmium-binding glycoproteins, termed FIIA and FIIB, had molecular weights of 8000 and 13,000 and consisted of 52 and 94 amino acid residues, respectively. Three and two cysteine residues in FIIA and FIIB, respectively, were found and two more half-cystine were also detected in FIIB. 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. Both showed strong metal-binding ability, especially for cadmium, copper, and mercury.