Cadmium can bind to the sulphhydryl groups in proteins and affect the structure and function of these molecules. MT is a cysteine-rich, metal-binding protein protecting cells from cytotoxic heavy metals, including cadmium, by sequestration (Liu et al. 1995, Waalkes 2000). It was shown earlier that cadmium induces MT in the abdominal muscle of C. crangon ( Napierska & Radłowska 1998). Cadmium is responsible for several toxic effects that lower the GSH level. In addition, cadmium induces oxidative processes in cells; GSH is the most efficacious antioxidant
(Wang et al. 2004). Cadmium complexing by reduced glutathione is one of the first defensive Doramapimod supplier reactions of animals (Bruggeman et al. 1992). GSH is an important intracellular tripeptide containing cysteine (present in cells up to 8 mM) ( Griffith 1999). Under normal physiological circumstances, at the expense of NADPH, oxidized glutathione (GSSG) is reduced to GSH by glutathione reductase, PARP inhibitor leading to a high GSH/GSSG ratio, thereby forming a redox cycle ( Canesi & Viarengo 1997, Griffith 1999, Lu 2000, Lee et al. 2008). Cadmium is an environmental contaminant in seawater that accumulates in organisms; it can be ingested by some animals through their food. It was shown earlier that the cadmium concentration in the abdominal muscles of C. crangon inhabiting the Gulf of Gdańsk is 10 times higher than that
in the abdominal muscles of shrimps Palaemon serratus from Concarneau Bay, Atlantic Ocean ( Napierska et al. 1997). The high level of cadmium in C. crangon muscles is due to the serious water pollution in the Gulf of Gdańsk, the region from where the shrimps were collected. In fish, cadmium can reach the blood via the alimentary canal, and the albumin present in the blood in high concentrations may act as a chelating agent of cadmium. Albumin is a 70 kDa protein containing about 7% cysteine in its amino acid sequence and can act as non-specific Sclareol chaperone to some enzyme activity. In this way, albumin can protect other protein molecules from direct cadmium binding, as has been shown for malic enzyme ( Figure 4 and 6). ME catalyses the reversible decarboxylation of malate to form pyruvate in the
presence of NADP coenzyme: the divalent manganese or magnesium cation is necessary to start the enzymatic reaction. Over the pH range 6.5–7.0, the rate of pyruvate carboxylation is equal to the rate of malate decarboxylation, suggesting an anaplerotic function for abdominal muscle ME in C. crangon ( Biegniewska & Skorkowski 1983). ME activity in crustacean and fish muscles is much higher than that observed in most terrestrial species ( Skorkowski 1988). ME is particularly interesting since it uses pyruvate as a substrate and provides an alternative route for pyruvate metabolism in fish muscle during the active mobilization of protein as an energy source or supports gluconeogenesis in the liver during salmon spawning migration ( Mommsen et al. 1980, Mommsen 2004).