Binding of trace elements (Ag, Cd, Co, Cu, Ni, and Tl) to cytosolic biomolecules in livers of juvenile yellow perch (Perca flavescens) collected from lakes representing metal contamination gradients.

Abstract

Biomolecules involved in handling cytosolic metals in the liver of the yellow perch (Perca flavescens) were characterized in juvenile fish collected from 4 lakes constituting metal contamination gradients. Using size-exclusion liquid chromatography coupled to an inductively coupled mass spectrometer, we determined metal distributions among ligands of different molecular weights in the cytosol, before and after a heat denaturation step designed to isolate metallothionein-like peptides and proteins. Silver, Cd, and Cu found in the heat-stable protein supernatants were indeed largely present as metallothionein-like peptide complexes; but Co, Ni, and Tl, also present in the heat-stable protein supernatants, did not coelute with metallothionein-like peptides and proteins. This difference in metal partitioning is consistent with the known preference of "soft" metals such as Ag, Cd, and Cu(I) for thiolated ligands and the contrasting tendency of Co and Ni to bind to ligands with oxygen and nitrogen as donor atoms. Metal handling in the whole cytosol also reflected these differences in metal-binding behavior. For Cd and Cu, the importance of the molecular weight pool that includes metallothionein-like peptides and proteins increased relative to the other pools as the total cytosolic metal concentration ([M]cytosol ) increased, consistent with a concentration-dependent detoxification response. In contrast, for Ni and Tl the increase in [M]cytosol was accompanied by a marked increase in the high-molecular weight (670-33 kDa) pool, suggesting that hepatic Ni and Tl are not effectively detoxified. Overall, the results suggest that metal detoxification is less effective for Ni, Tl, and Co than for Ag, Cd, and Cu. Environ Toxicol Chem 2018;37:576-586. © 2017 SETAC.