Metal pollution pose one of the most serious threats to the environment and human health. Metals enter the biosphere through natural processes as well as through human activities such as mining, fuel burning, and a variety of other industrial operations [21].
Metals can interfere with the intracellular detoxification processes of organic contaminants which may cause amplification of their toxicity. Glutathione transferases (GSTs) are important proteins in the detoxification of both organic xenobiotics and endobiotic metabolites. When metals enter an organism, the defensive system against oxidative stress and other negative consequences increases GST activity. However, there is increasing evidence that metals at hazardous quantities have an effect on GSTs, either directly by inhibiting enzyme activity or indirectly by lowering the concentration of reduced glutathione [22].
Glutathione (GSH) is a tripeptide that is produced in the liver and present in cytosol, nucleus and mitochondria of cells. The GSH/GSSG ratio indicates the cell's oxidative status [23]. One of the two primary roles of glutathione, which is plentiful in the cell cytosol, is to eliminate harmful metabolites from the cell, and the other is to keep the sulfhydryl groups stable due to its reduced form [24]. GSH has reduced thiol groups which enable it to serve as antioxidant [25, 26].
All living species in nature are in risk of extinction as a result of the world's rising environmental degradation. It is critical to consume nutrients that boost the body's resilience against this critical threat. Enzymes roles in living organisms are to keep critical functions healthy and sustained. GST enzyme, which is one of the most essential enzymes that will give our bodies with resistance, detoxifies xenobiotics and is a well-known enzyme in the detoxification of xenobiotic chemicals [27]. GST enzyme, a dimeric enzyme, is responsible for the conjugation of xenobiotics with reduced glutathione. As a result, GSTs offer phase II transformation of endogenous chemicals and xenobiotics such as anticancer medicines and environmental carcinogens produced as a result of oxidative stress, rendering xenobiotics soluble and eliminated from the body via bile and urine [28].
Türkan et al. investigated the inhibition of some heavy metals on the GST enzyme of Cherry Laurel (Prunus laurocerasus L.). In that study, it was found that Cd2+, Ni2+, Cu2+, and Mg2+ have an inhibition effect on Cherry Laurel GST enzyme. The IC50 values of these heavy metals were between 0,33 and 1.79 mM, while the most strongly inhibiting heavy metal was found to be Mg2+ [13]. Another study reported by Halušková et al. investigated heavy metal application for barley [29]. Balcı et al. investigated the inhibition of some metal ions in Vaccinium arctostapylous L. The IC50 values for Cd2+, Cu2+, Ni2+, and Mg2+ inhibition values used in the studywere found as 0.502, 0.701, 0.789, and 0.127 mM, respectively. Mg2+ was found to be the most effective inhibitor [30].
Heavy metals affect not only plants but also animals. Ozaslan et al 2017 reported inhibition analysis of GST enzyme with metal ions from the Van Lake fish gills (Chalcalburnus tarichii Pallas). In the study, it was found that Ag+, Cu2+, Cd2+ and Zn2+ ions had inhibitory effects on the enzyme. The IC50 values were found to be 16.43, 320.25, 450.32 and 1510.13 µM, respectively. Ag+ showed better inhibitory effect compared with other metal ions [31]. In another study, inhibition effects of Al+ 3, B+ 3, Ba+ 2, and Se− 2 metal ions on the GST enzyme of gill tissue of Van Lake Pearl Mullet (Chalcalburnus tarichi) were investigated by Zaric. The IC50 values of these metal ions were calculated as 0.072 mM, 0.100 mM, 0.082 mM and 0.083 mM, respectively [32]. Taysi and Temel 2021 investigated the inhibition effects of Ag+, Cd2+, Ni2+, Zn2+ and Al3+ metals on quail liver GST enzyme. The IC50 values of these metals were 239, 258, 265, 322, 594 µM, respectively. The most strongly inhibiting heavy metal was found to be Ag+ [33]. In another study Ahmed et al. reported the inhibition of metal ions on GST enzyme characterized from quail heart tissue. In the study, it was determined that Cu2+, Ag+ and Cd2+ metals caused significant decrease in enzyme activity. The IC50 values of these metals were 0.0028, 0.382 and 3.127 mM, respectively. The strongest inhibitory metal was found to be Cu2+ [34]. In the study of Akkemik et al. 2012, GST enzyme was purified from turkey liver and heavy metal inhibition was investigated. As a result of the research, inhibition of Ag+, Cu2+ and Hg2+ metals was observed. The IC50 values were found to be 0.378, 245 and 257, respectively. Ag + was found as the metal with the strongest inhibition [35]. Aksoy et al. investigated the inhibition effect of Ag+, Cu2+, Pb2+, Ni2+ and Zn2+ metals on GST from the muscle tissue of Lake Van fish (Chalcalburnus tarichii Pallas). The IC50 values of these metals were found as 0.011, 0.103, 0.113, 2.5, 0.253 mM, respectively. Ag was found to be the metal with the strongest inhibitory effect [36]. As can be seen from the provided literature data, our findings are in good agreement with the previous investigations on GST enzymes from different sources.