engleski

Metallothionein and metal quantification in the whole mussel tissue

Metallothioneins (MTs) are low molecular mass proteins with high cysteine content and as a consequence have a high metal-binding affinity. MTs are inducible by many toxic metals among which cadmium is the strongest inducer. Increased concentrations of contaminants, heavy metals in the first place, in water column would be expected to cause the increase in MT content in mussels transplanted from the clean site and caged for the period of one month. Preparation of S50-fraction from mussel tissue has been performed according to the procedure proposed by Bequalm project with the necessary adjustments needed due to sensitivity of mussel MTs to oxidation. Quantification of mussel MT has been performed in heat-treated S-50 fraction using differential pulse voltammetry (DPV). It is based on the linear relationship between catalytic hydrogen wave and the concentration of cystein residues. In the same heat-treated S-50 fractions metal contents (Cd, Cu, Zn) have been determined using flame AAS. Concentrations of MT measured in heat-treated S-50 fraction isolated from whole mussel tissue are recorded in the range from 151 ug/mL (0-time mussels) to 545 ug/mL (Station G4). The lowest values are reported for 0-time mussels, i.e. in mussels prior to caging. Based on MT data analysis of variance showed that there is a statistically significant difference between stations in German Bight (GB) and 0-time mussels. On the contrary, the data for Statfjord (St) showed no significant difference. Analysing the data of MT expressed per gram of total cytosolic proteins no statistically significant difference has been found between stations in areas GB and St. Cadmium concentrations measured in S-50 fractions are comparable at GB stations and 0-time, and the values at St stations are 3 times higher than those in 0-time mussels. There is no significant difference in copper and zinc concentrations between the stations in both areas. In general, MT, whole mussel tissue mass and metal data show high variability between individual mussels. Cadmium concentration in S-50 fractions significantly differ at St stations in comparison with 0-time mussels, which indicates the enhanced Cd concentrations in the water column. These results are in agreement with total Cd analysis in whole mussel tissue (Becpelag data). The MT analysis in whole mussel tissue is not optimal if the response of an organism to metal pollution should be detected. For that purpose organs like gills or digestive gland (hepatopancreas) might be preferable.

metallothioneins; heavy metals; Mytilus edulis

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