Glutathione transferase P1-1 (GSTP1-1) is expressed in some human tissues and is abundant in mammalian erythrocytes (here termed e-GST). This enzyme is able to detoxify the cell from endogenous and exogenous toxic compounds by using glutathione (GSH) or by acting as a ligandin. This review collects studies that propose GSTP1-1 as a useful biomarker in different fields of application. The most relevant studies are focused on GSTP1-1 as a biosensor to detect blood toxicity in patients affected by kidney diseases. In fact, this detoxifying enzyme is over-expressed in erythrocytes when unusual amounts of toxins are present in the body. Here we review articles concerning the level of GST in chronic kidney disease patients, in maintenance hemodialysis patients and to assess dialysis adequacy. GST is also over-expressed in autoimmune disease like scleroderma, and in kidney transplant patients and it may be used to check the efficiency of transplanted kidneys. The involvement of GSTP in the oxidative stress and in other human pathologies like cancer, liver and neurodegenerative diseases, and psychiatric disorders is also reported. Promising applications of e-GST discussed in the present review are its use for monitoring human subjects living in polluted areas and mammals for veterinary purpose.

Protein cysteines often play crucial functional and structural roles, so they are emerging targets to design covalent thiol ligands that are able to modulate enzyme or protein functions. Some of these residues, especially those involved in enzyme mechanisms—including nucleophilic and reductive catalysis and thiol-disulfide exchange—display unusual hyper-reactivity; such a property is expected to result from a low pK_a and from a great accessibility to a given reagent. New findings and previous evidence clearly indicate that pK_a perturbations can only produce two–four-times increased reactivity at physiological pH values, far from the hundred and even thousand-times kinetic enhancements observed for some protein cysteines. The data from the molten globule-like structures of ribonuclease, lysozyme, bovine serum albumin and chymotrypsinogen identified new speeding agents, i.e., hydrophobic/electrostatic interactions and productive complex formations involving the protein and thiol reagent, which were able to confer exceptional reactivity to structural cysteines which were only intended to form disulfides. This study, for the first time, evaluates quantitatively the different contributions of pK_a and other factors to the overall reactivity. These findings may help to clarify the mechanisms that allow a rapid disulfide formation during the oxidative folding of many proteins.

Many details of oxidative folding of proteins remain obscure, in particular, the role of oxidized glutathione (GSSG). This study reveals some unknown aspects. When a reduced ribonuclease A refolds in the presence of GSSG, most of its eight cysteines accomplish a very fast glutathionylation. In particular, one single cysteine, identified as Cys95 by mass spectrometry, displays 3600 times higher reactivity when compared with an unperturbed protein cysteine. Furthermore, the other five cysteines show 40–50 times higher reactivity toward GSSG. This phenomenon is partially due to a low pK_a value of most of these cysteines (average pK_a = 7.9), but the occurrence of a reversible GSSG-ribonuclease complex (K_D = 0.12 mM) is reasonably responsible for the extraordinary hyper-reactivity of Cys95. Neither hyper-reactivity nor some protein-disulfide complexes have been found by reacting a reduced ribonuclease with other natural disulfides i.e., cystine, cystamine, and homocystine. Hyper-reactivity of all cysteines was observed toward 5,5’-dithiobis-(2-nitrobenzoic acid). Given that GSSG is present in high concentrations in the endoplasmic reticulum, this property may shed light on the early step of its oxidative folding. The ultra-rapid glutathionylation of cysteines, only devoted to form disulfides, is a novel property of the molten globule status of the ribonuclease.

The aim of this study was to evaluate the influence of hidden environmental pollution on some blood parameters of sheep to detect susceptible biomarkers able to reveal slight contamination. Four dairy sheep farms, two with semi-extensive and two with intensive type systems were involved in this study. Two farms in different systems were chosen as properly located in a southern area of Latium (Italy), close to the Sacco River, in which contamination with β-hexachlorocyclohexane (β-HCH) occurred in the past due to industrial waste. A recent study established the presence of low but detectable residual contamination in these areas. The other two farms were outside the contaminated area. Erythrocyte glutathione transferase (e-GST) and oxidative stress parameters were monitored as well as some immune response and metabolic profile parameters throughout the investigated period of four months. The present study showed a relevant and significant increase in e-GST (+63%) in the extensive farming system of the contaminated area, whereas some immune response biomarkers, i.e., white blood cells, neutrophils, lymphocytes, and lysozyme resulted within the physiological range. In all farms, oxidative stress and acute phase response parameters were also within the physiological range. Our results suggest that e-GST is a very effective alarm signal to reveal “hidden” persistent contamination by β-HCH, and reasonably, by many other different dangerous pollutants.

Glutathione has long been suspected to be the primary low molecular weight compound present in all cells promoting the oxidative protein folding, but twenty years ago it was found “not guilty”. Now, new surprising evidence repeats its request to be the “smoking gun” which reopens the criminal trial revealing the crucial involvement of this tripeptide.