The inhibition kinetics of yeast glutathione reductase by some metal ions

Abstract

Glutathione reductase (GR, type IV, Baker's yeast, E.C 1.6.4.2) is a flavoprotein that catalyzes the NADPH-dependent reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH). In this study some metal ions have been tested on GR; lithium, manganese, molybdate, aluminium, barium, zinc, calcium, cadmium and nickel. Cadmium, nickel and calcium showed a good to moderate inhibitory effect on yeast GR. GR is inhibited non-competitively by Zn2+ (up to 2 mM) and activated above this concentration. Ca2+ inhibition was non-competitive with respect to GSSG and uncompetitive with respect to NADPH. Nickel inhibition was competitive with respect to GSSG and uncompetitive with respect to NADPH. The inhibition constants for these metals on GR were determined. The chelating agent EDTA recovered 90% of the GR activity inhibited by these metals.

Increase in intracellular free/bound NAD[P]H as a cause of Cd-induced oxidative stress in the HepG2 cells

“…A change in their interconversion may reflect a disruption in the activity of these enzymes. Thioredoxin reductase, glutathione reductase, phosphoglycerate dehydrogenase, NADH Coenzyme Q reductase, mitochondria glycerol-3-phosphate dehydrogenase, biliverdin reductase A as well as the nucleoside diphosphate linked moiety and mitochondrial apoptosis inducing factor (AIF) (HomoloGene link database for human cells, Pubmed) are enzymes known to bind to NAD[P]H. In the case of glutathione reductase, recent study by Tandogan and Ulusu (2007) showed that Cd can inhibit its activity in yeast. Although it is not clear how the inhibition reaction occurred, it is possible that Cd displaces NAD[P]H from this enzyme and interferes with its ability to carry out the reduction reaction.…”

Inhibition of Disulfide Reductases as a Therapeutic Strategy

“…For example, it has been demonstrated that yeast glutathione reductase can be deactivated by Fe(II) and inhibited by other metal ions such as cadmium, nickel and calcium [72,73]. Thus, metal-based compounds can be pursued as a mechanism of inhibiting Gor in pathogens.…”

Glutathione Reductase from Oryza sativa Increases Acquired Tolerance to Abiotic Stresses in a Genetically Modified Saccharomyces cerevisiae Strain

“…The molecular mass of the homodimeric GR enzymes is about 55 kDa. It has been noted that in the absence of thiols (redox active sites), GR has a tendency to form tetramers and larger complexes [28]. In addition, the nucleotide (FAD) binding domain (yellow box), NADPH binding domain (blue box), proton acceptor (green box), and modified residue (violet box) are conserved (Fig.…”

“…The enzyme contains a redox-active disulfide in its active site and requires NADPH for its catalytic activity. In the absence of thiols, GR has a tendency to form tetramers and larger complexes [28]. To date, cDNA molecules encoding GR have been found in many types of organisms including bacteria, plants, and yeast as well as higher eukaryotes such as mice and humans [19].…”

“…Living organisms are protected against the damaging effects of these molecules by a broad range of systems. GR is involved in cellular defense mechanisms that offer protection from the harmful effects of endo-and exogenous hydroperoxides [28]. Aside from defending against free radicals and ROS, GR also has roles in protein and DNA biosynthesis, and maintaining a high GSH/GSSG ratio [11].…”