Enzymatic mobilisation of trace metals from estuarine sediment

Proteinase K, a non-specific protease that is representative of enzymes encountered in the digestive environment of deposit-feeding organisms, has been employed to determine the nature and extent of enzymatic mobilisation of trace metals (Al, Fe, Mn, As, Cu, Pb and Zn) from contaminated estuarine sediment. The extent of metal release by the enzyme was critically dependent on whether and how the sample had been dried and, for all metals except Mn, mobilisation was greatest when the sample had not been dried. The fraction of metal available to the enzyme, f_e, defined as the amount of metal released from undried sediment after 4 h incubation relative to the total metal concentration, was less than 1% in all cases. Significantly, however, there was a strong correlation between f_e and published factors defining the enrichment of metals in the gut fluids of the deposit-feeding lugworm, Arenicola marina. This suggests that, at least qualitatively, the mechanics of metal mobilisation in situ are replicated by the commercial enzyme. Thermally denaturing the enzyme resulted in mobilisation that was greater than (As and Cu) or similar to (all other metals) release engendered by the active enzyme, suggesting that the principal mechanism of metal mobilisation is not related to proteolysis but more likely involves complexation or exchange with component amino acids of the enzyme.