engleski

Deeper insight into the metallome of the digestive glands of Unio crassus mussels at different metal exposures: Distribution of metals among cytosolic biomolecules.

Metallomics, a recently developed field of metal and metalloid research, focuses on the determination of the distribution of metals in cells and tissues and their interactions with cellular components, in addition to the quantification of metals. Mussels are generally recognised as useful biological indicators of aquatic pollution at both the organic and cellular levels, while the digestive gland is the central detoxifying organ of the organism. The cytosolic fraction of the tissue metallome contains a metabolically active and therefore potentially toxic fraction of metals, while cytosolic metalloproteins are one of the most common targets of toxic metals. The combination of size-exclusion liquid chromatography (SEC) and inductively coupled plasma mass spectrometry (ICP-MS) is a useful tool for screening metal distribution among the different molecular mass biomolecules. Using the above methodology, the focus of this study was to establish cytosolic profiles of several essential (Cu, Fe, Zn) and non-essential elements (Ag, Cd, Pb) and to define the masses of metal- binding biomolecules in the digestive gland of the freshwater mussel Unio crassus from two sites of the Mrežnica River with different anthropogenic influences: the industrial area of the city of Karlovac (KAR) as a polluted site and location upstream of the city of Duga Resa as a reference site (REF). Cytosolic Ag, Cd and Pb were mostly bound to components of cytosol eluting in the high molecular mass (HMM ; >300 kDa) and low molecular mass (LMM ; 10-40 kDa) regions, but with greater elution in the LMM peak, which presumably contained metallothioneins (MT). The distribution profile of essential metal Cu was similar to the previously mentioned highly toxic metals. This suggests that MT plays a crucial role in the homeostasis of essential metals as well as in the detoxification of toxic metals. Iron had a peak in the HMM area, which roughly coincided with ferritin, the major Fe storage protein in almost all organisms. Zinc eluted in a wide range of molecular masses (10-750 kDa), indicating the binding of Zn to a large number of proteins, which is consistent with its importance in many biological processes. In general, the chromatographic profiles obtained at both sites were comparable for all elements studied, suggesting that the same cytosolic biomolecules are involved in metal binding at different levels of metal accumulation. Quantitative differences in element profiles between the two sites, visible as different peak heights, were found for Cd, Cu, Fe and Pb and were consistent with significant differences in total cytosolic element concentrations between sites. These results suggest that the distribution of selected essential and non-essential elements among different cytosolic ligands may serve as a potential indicator of metal exposure. Therefore, further separation and characterization of cytosolic metal-binding biomolecules would be useful.

metallome ; mussels ; metals ; cytosol ; HPLC ; ICP-MS

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