The glutathione S-transferases (GST) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties: the cytosolic enzymes are encoded by at least five distantly related gene families (designated class alpha, mu, pi, sigma, and theta GST), whereas the membrane-bound enzymes, microsomal GST and leukotriene C, synthetase, are encoded by single genes and both have arisen separately from the soluble GST. Evidence suggests that the level of expression of GST is a crucial factor in determining the sensitivity of cells to a broad spectrum of toxic chemicals. In this article the biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress.A description of the mechanisms of transcriptional and posttranscriptional regulat...

The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance.

Metallothioneins in aquatic invertebrates : their role in metal detoxification and their use as biomarkers

Metallothioneins in metal regulation and toxicity in aquatic animals

This review compiles and evaluates existing scientific information on the use, limitations, and procedural considerations for EROD activity (a catalytic measurement of cytochrome P4501A induction) ...

Ethoxyresorufin-O-deethylase (EROD) activity in fish as a biomarker of chemical exposure.

http://wgbis.ces.iisc.ernet.in/energy/stc/biomonitoring_of_wetlands/biomonitoring_aquatic_ecosystem.pdf

Biomonitoring: An appealing tool for assessment of metal pollution in the aquatic ecosystem

An investigation of the mechanisms of detoxication of copper and zinc by the oyster Ostrea edulis (L) has been carried out using naturally occurring “green-sick” (contaminated by copper) and unpolluted oysters. Electron microprobe X-ray analysis of tissues in the electron microscope gives direct evidence for the structural compartmentation of copper and zinc in separate, specific, granular amoebocytes. The metals are immobilized in membrane-limited vesicles as different chemical compounds, copper being associated with sulphur and zinc with phosphorus. Chemical analyses of serum and tissues of normal and “green-sick” oysters indicate that (a) Cu and Zn are accumulated independently, (b) the Cu and Zn in the serum, while higher than in the surrounding sea water, are maintained at a 10-fold smaller level than the tissues, (c) toxicity is reduced by active uptake from the serum into granular amoebocytes, where it is further reduced by compartmentation in membrane-limited vesicles. It is calculated that the individual cell types may contain as much as 13,000 ppm Cu and 25,000 ppm Zn.

Detoxication of metals by marine bivalves: An ultrastructural study of the compartmentation of copper and zinc in the oyster Ostrea edulis

The kinetics of accumulation and excretion of ferric hydroxide in Mytilus edulis (I.) and its distribution in the tissues

Current concepts of metal metabolism have been reviewed with a view to understanding the factors that influence the uptake, storage and elimination of essential and pollutant trace metals in aquatic organisms. Examples from our own studies on estuarine molluscs exposed to heavy metals have been used to illustrate these factors. When metal uptake was combined with electron microscope studies, a novel storage and detoxication mechanism was revealed, where formation of vesicles within the cell enclose the metal within a membrane. This prevents contact of excess metal with vital constituents and effectively detoxifies it until eliminated or passed on to other tissues, as required. The generality of this mechanism has been established.

Mechanisms of immobilization and detoxication of metals in marine organisms

Isolation and elemental analysis of metal-rich granules from the kidney of the scallop, Pecten maximus (L.)

The accumulation of cadmium was investigated in two species of oysters [Crassostrea gigas (L.) and Ostrea edulis (L.)] from the same environment and in oysters of the same species (O. edulis) from two different environments (contaminated and uncontaminated), under controlled laboratory conditions (33‰ salinity, 10°C, 100 μg Cd l-1) for up to 111 d in 1982. C. gigas accumulated cadmium twice as fast as O. edulis (1.07 vs 0.52 μg Cd g-1 wet wt d-1). Furthermore, O. edulis from an uncontaminated environment accumulated cadmium faster than O. edulis from a metal-contaminated environment (0.52 vs 0.34 μg Cd g-1 wet wt d-1). There was no effect of cadmium exposure on total soft-tissue copper and zinc concentrations. Investigation of cytosolic metal-binding using Sephadex G-75 gel-permeation chromatography indicated that binding to very low molecular weight ligands (MW 70% of the cytosolic zinc in all oysters and>40% of the cytosolic cadmium in all oysters except O. edulis from Conwy at 83 d. In copper-contaminated oysters, excess copper was also associated with very low molecular weight ligands. Intermediate molecular weight cadmium/copper-binding proteins (similar to metallothionein in molecular weight) were observed in the cytosol and were shown to differ between species in terms of their behavior on Sephadex G-75. Finally, the distribution of accumulated cytosolic cadmium in O. edulis from the contaminated environment was shown to have a unique distribution, i.e., there was no cadmium associated with high molecular weight cytosolic macromolecules. The data indicate that both genetic and environmental factors influence cadmium accumulation in oysters.

S.G. George

Papers

Detoxication of metals by marine bivalves: An ultrastructural study of the compartmentation of copper and zinc in the oyster Ostrea edulis

The kinetics of accumulation and excretion of ferric hydroxide in Mytilus edulis (I.) and its distribution in the tissues

Mechanisms of immobilization and detoxication of metals in marine organisms

Isolation and elemental analysis of metal-rich granules from the kidney of the scallop, Pecten maximus (L.)

Cadmium kinetics in oysters ― a comparative study of Crassostrea gigas and Ostrea edulis