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Abstract
Cadmium, lead and mercury are environmentally persistent toxicants that affect tissues and cellular components or exert an effect on generation of reactive oxygen species causing a decreased level of available antioxidant reserves. Sulfurtransferases are enzymes that are widespread in nature. Rhodanese, 3-mercaptopyruvate sulfurtransferase and γ-cystathionase play an important role in the metabolism of L-cysteine. Heavy metal ions can bind to -SH groups of cysteine residues in their active sites and, therefore, decrease the activity of these enzymes and result in changes in the level of sulfane sulfur-containing compounds, products of L-cysteine desulfuration. Changes in the activity of sulfurtransferases were investigated in the kidneys, heart, brain, liver and skeletal muscle of Marsh frogs (Pelophylax ridibundus) after 10 days of exposure to Pb(NO3)2 at the concentration of 28 mg/L and CdCl2 at the concentration of 40 mg or 80 mg/L, and in Xenopus laevies tissues after 7 and 14 days of exposure to HgCl2 at the concentration of 1.353 mg/L. The investigated heavy metal ions have a tendency to inhibit the activity of sulfurtransferases and decrease the level of glutathione, what can result in oxidative stress and oxidation of cysteine -SH groups to -SOH. This reversible oxidation and reduction of these redox sensitive groups can play a role in defenses against oxidative stress. Based on the presented results, one can surmise that also the expression of the three sulfurtransferases depends on heavy metal ions and/or some parameters of oxidative stress, what can explain the increase of the activity of MPST and CST in the kidney.
Highlights
Environmental contamination is a growing problem around the world
Based on the presented results, one can surmise that the expression of the three sulfurtransferases depends on heavy metal ions and/or some parameters of oxidative stress, what can explain the increase of the activity of MPST and CST in the kidney
Intensive transformation of sulfane sulfur-containing compounds by sulfurtransferases takes place [11]. These results indicate an increase in the level of enzymatic proteins in the cells of the kidney e.g. in response to oxidative stress [13] and this can confirm the participation of sulfurtransferases in antioxidative protection in the kidneys
Summary
Environmental contamination is a growing problem around the world. One of the most important global issues is chronic, low-level exposure to heavy metals. Lead and mercury are toxicants that cause neurological, hepatological, reproductive and gastrointestinal pathologies [1,2,3,4]. There are three main reasons of heavy metal toxicity: 1) direct interactions with proteins due to their high affinities for thiol-, histydyl-, carboxyl-groups, influencing their structure, catalytic and transport functions in cells; 2) stimulated generation of reactive oxygen species (ROS) that modify the antioxidant defense and increase oxidative stress; 3) displacement of essential cations from specific binding sites, causing major disruption of their function [5]. Lead is chemically very similar to calcium and it competes with or mimics the action of calcium [6].
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