Multiple forms of metallothionein from the digestive gland of naturally occurring and cadmium-exposed mussels, Mytilus galloprovincialis

Abstract

Polymorphism of metallothioneins in the digestive gland of naturally occurring (control) and experimentally Cd-exposed mussels Mytilus galloprovincialis (200 µg Cd l -1 ; 14 days) was studied by applying the conventional methods of Sephadex column liquid chromatography , and by an electrochemical method (DPASV) for determination of Cd, Zn and Cu concentrations in chromatographic fractions. In both control and Cd-exposed mussels, two distinct molecular mass components of the metallothioneins, monomeric (MT-10) and dimeric (MT-20), were resolved by Sephadex G-75 gel filtration chromatography. In control mussels, the MT-10 component was predominantly expressed as containing markedly higher constitutive levels of Zn (100×) and Cu (10×) than of Cd. Each of these two molecular mass components was further resolved into seven metal-rich peaks by anion-exchange chromatography. In Cd-exposed mussels the larger proportion of Cd was bound to the MT-20 than to the MT-10 component, suggesting that the dimeric component may be considered as a primarily inducible metallothionein. The elution positions of metal-binding maxima of Cd-exposed and control mussels on the respective DEAE chromatographic profiles were comparable. A great similarity in elution positions of Cd maxima between the composite and single-specimen samples was also observed. Our study confirms a high multiplicity of MT forms in mussels from the Mytilus genus not only under the laboratory high-level metal exposure conditions, but also at a natural seawater metal exposure level. The ecotoxicological significance of dimeric and monomeric MT forms, as well as their possible application in the biomonitoring of seawater for trace metals, has been considered.

Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy‐Resolution XANES Spectroscopy

“…The level of MT in ME was increased previously by exposure to cadmium or mercury, and two isoforms of apparent molecular weight 12 kDa (MT‐10) and 20 kDa (MT‐20) were isolated by polyacrylamide gel electrophoresis . Here, MTs were induced at Hg(NO 3 ) 2 concentration (100 μg Hg II L −1 or 0.1 ppm Hg) and exposure time (9 days) broadly similar to those in previous HgCl 2 (0.01 to 0.04 ppm for up to 21 days) and CdCl 2 experiments (0.1 ppm for 11 days, 0.1 ppm for 3–4 months, 0.2 ppm for 14 days, 0.2 ppm for 3–4 months, and 0.4 ppm for 22 days) and extracted by thermal denaturation (see the Experimental Section).…”

“…The Hg:Cu:Zn molar stoichiometry, as determined from elemental analysis of the MT extracts using inductively coupled plasma mass spectrometry (ICP‐MS), is 0:1:1 in the control and 2:2:5 in the Hg mussels. The constitutive levels of Cu and Zn in naturally occurring MTs are consistent with previous observations and with the role of MTs in the intracellular homeostasis of the two essential metals . The total number of metals bound per molecule of MT was calculated by dividing the sum of the metals concentration in the MT extracts by the weight concentration of MTs in the same extracts and taking a MT‐10 molecular weight of 7.24 kDa .…”

Biogenesis of Mercury–Sulfur Nanoparticles in Plant Leaves from Atmospheric Gaseous Mercury

“…In Mytilidae, MT dimers are transcriptionally induced from DNA following specific exposure to Cd(II), not to Zn(II) nor Cu(I), and are enriched in Cd relative to the monomeric form. [118][119][120][121][122][123] We conclude from this that the -HgSNP-type structure identified by HR-XANES could be a mercury-cysteinate cluster of approximate stoichiometry Hg7Cys16.…”

Transfer and efflux of cadmium and silver in marine snails and fish fed pre‐exposed mussel prey

“…For the remaining peaks, their elution times and shapes remained comparable to those of the controls. Ivankovic et al [33] showed that MT-20 was primarily induced in Mytilus galloprovincialis after Cd exposure and represented a Cd-induced form of MT. Two molecular size classes of MT (MT-10 and MT-20) [16,31] have been suggested to play different roles in metabolism and detoxification of metals [32].…”