Role Of Thiols Research Articles

The Role of Thiol and Ischemia Modified Albumin in the Evaluation of Intensive Care Necessity in COVID-19 Cases

Amaç: Korona virüs hastalığı (COVID 19) 4,5 milyondan fazla insanın ölümüne sebep olmuş küresel bir halk sağlığı sorunudur. Bu çalışmada, yataklı servis ve yoğun bakım ünitesinde tedavi alan COVID-19 hastalarının tiyol ve iskemi modifiye albumin (İMA) düzeylerinin, hastaların mevcut klinik durumu ve hastalığın seyri ile olan ilişkisinin değerlendirilmesi amaçlanmıştır. Materyal ve metod: Bu çalışmaya, PCR testi ile pozitif olduğu doğrulanmış, COVID-19 enfeksiyonu tanısı alan 300 hasta dahil edilmiştir. Hastalar tedavi edildiği birim esas alınarak iki gruba ayrılmıştır. Bu hastaların 160’ı serviste (grup 1), 140’ı yoğun bakım birimlerinde (grup 2) tedavi edilmiştir. Hastaların numunelerinde tiyol, İMA, CRP, ferritin ve lenfosit düzeylerinin ölçümü gerçekleştirilmiştir. Bulgular: Gruplar karşılaştırıldığında grup 2’nin tiyol düzeyleri önemli derecede düşük bulunmuştur (p<0,001). Ayrıca grup 2’nin İMA düzeylerinin, grup 1’e göre anlamlı düzeyde yüksek olduğu gözlenmiştir (p<0,001). Diğer laboratuvar testleri değerlendirildiğinde, grup 2’nin CRP ve ferritin düzeyi yüksek (p<0,001), lenfosit sayısı ise düşük (p<0,001) olarak belirlenmiştir. Tiyol düzeyleri ile CRP, ferritin, lenfosit ve İMA düzeyleri arasında anlamlı korelasyon saptanmıştır (sırasıyla r=-0,58; p<0,001, r=-0,41; p<0,001, r=-0,32; p<0,001, r=-0,39; p<0,001 ). Ayrıca İMA düzeyleri ile CRP, ferritin, lenfosit ve tiyol düzeyleri arasında anlamlı korelasyon gözlenmiştir (sırasıyla r=0,19; p=0,02, r=0,18; p=0,043, r=-0,15; p=0,047, r=-0,39; p<0,001). Sonuç: COVID-19 hastalarında güçlü bir antioksidan olan tiyol düzeyinin azalması, oksidatif strese sebep olan mevcut inflamatuvar süreçten kaynaklanmakla beraber tromboza sekonder gelişen iskemik şartlara bağlı oksidatif stresin etkisi ile de ortaya çıkmış olabileceğini düşündürmektedir. Dolayısıyla inflamatuvar sürecin ve trombotik olayların daha şiddetli olarak gözlendiği yoğun bakım hastalarında İMA düzeylerinin artması, tiyol düzeylerinin azalmasını destekleyecek niteliktedir. Sonuç olarak yataklı serviste ve yoğun bakım ünitesinde tedavisi gerçekleştirilen COVID-19 hastalarının tiyol ve İMA düzeylerinin belirlenmesi, hastaların mevcut klinik durumu ve hastalığın seyri hakkında yardımcı olabilecek bir potansiyele sahip olduğunu düşündürmektedir.

Evaluation of the role of thiol / disulfide homeostasis in the etiology of idiopathic male infertility with a novel and automated assay

ABSTRACT Idiopathic male infertility (IMI) is the absence of a reason to explain a patient's infertility, and it occurs at a frequency of %31. In this study we aimed to investigate the oxidant/antioxidant status of patients with IMI and compare their results to those of healthy controls.A total of 79 patients with IMI (group 1) and 90 healthy individuals (group 2) were included in the study. We used Erel & Neşelioğlu’s thiol/disulfide homeostasis test. Collective and individual measurements of oxidative/antioxidative balance components were carried out by this novel thiol/disulfide homeostasis test. Serum antioxidant (total thiol (toSH), native thiol (SH)) and oxidant (disulfide (SS)) levels of all study participants were measured. The results from both groups were compared and analyzed statistically. After toSH, SH, and SS levels were determined, SS/toSH% and SS/SH% levels for each group were analyzed separately and compared statistically.The toSH, SH levels, and SS/SH%, SS/toSH% ratios were significantly different between the groups (p < 0.05).While antioxidant parameters (toSH and SH values) decreased in group1, oxidant parameters (SS/SH%, SS/toSH%) increased significantly. Although SS values were higher in group 1, the difference was not significant (p = 0.214). The SH cutoff value of 507.15 µmol/L predicted the probability of IMI development with 72.2% sensitivity and 74.4% specificity and toSH cutoff value of 545.45 µmol/L predicted IMI development with 70.9% sensitivity and 73.3 specificity (p < 0.001). Multivariate logistic regression analysis showed that the only independent risk factor for the development of IMI is SH. Patients with IMI had a significant change in their thiol/disulfide homeostasis, which suggests the involvement of this imbalance in the pathophysiology of IMI. Furthermore, these results also support the notion of the involvement of oxidative stress in sperm dysfunction. It also points to the possibility of using antioxidants in IMI treatment. Abbreviations: IMI: idiopathic male infertility; toSH: total thiol; SH: native thiol; SS: disulfide; OS: oxidative stress; ROS: reactive oxygen species; DCF: dichlorofluorescein; MiOXSYS: male infertility oxidative system; MOSI: male oxidative stress infertility; LC: L-carnitine; LAC: L-acetylcarnitine; Vit: vitamin; OAT: oligoasthenozoospermia; TMSC: total motile sperm count; WHO: World Health Organization; BMI: body mass index; DTNB: 5,5ʹ‐dithiobis‐2‐nitrobenzoic acid; CV: coefficient variation; ROC: receiver operating characteristic; PR: progressive, NP: non-progressive.

Differential responses of thiol metabolism and genes involved in arsenic detoxification in tolerant and sensitive genotypes of bioenergy crop Ricinus communis.

Castor, a non-food, dedicated bioenergy crop, has immense potential to be used for phytoremediation/revegetation of heavy metal contaminated sites. In the previous study, we identified arsenate [As(V)]-tolerant (WM) and As(V)-sensitive (GCH 2) genotypes of castor (Ricinus communis L.) with differential accumulation and tolerance of arsenic [As]. The role of thiols in As(V) toxicity and tolerance mechanism in the castor plant is not fully understood. On the one hand, thiol-dependent reduction of As(V) to As(III) by arsenate reductase (AR) makes it capable of reacting with thiol groups of protein leading to disturbed metabolic pathways; on the other hand, reduction of As(V) to arsenite [As(III)] by AR and then complexation of As(III) with phytochelatins (PCs) and compartmentalization of As(III)-PC complex are considered as the major detoxification mechanisms of As(V). In our study, the expression of RcAR increased in leaves and roots of As(V)-tolerant castor genotype WM but decreased in sensitive genotype GCH 2 due to 200 μM As(V) treatment. The activity of glutathione reductase (GR) increased significantly in the tolerant genotype, whereas it remained same in the sensitive genotype. GSH/GSSH ratio declined substantially in the sensitive genotype. The increased expression of phytochelatin synthase 1 isoform 1 (RcPCS1X1) in roots, RcPCS1X2 and metallothionein type 2 (RcMT2) in leaves, and c-type ABC transporter (RcABCC) in roots and leaves of WM was observed, but the expression of these genes declined or remained the same in GCH 2. Overall, our results suggest the essential roles of GR, RcAR, RcPCS1, RcMT2, and RcABCC in the tolerance of WM castor genotype to As(V) toxicity.

The role of thiol–disulfide homeostasis in neonatal sepsis

Background and aim The thiol–disulfide homeostasis is essential for the body to maintain effective antioxidant defense mechanisms. We aimed to show the relationship between sepsis and thiol–disulfide homeostasis in newborns. Materials and methods In this prospective study, 66 newborns with sepsis (group 1) and 51 healthy controls (group 2) were included. In group 1, 53 newborns were diagnosed as clinical sepsis (group 1a) and 13 as definite sepsis (group 1b). The study has two time points; the day of diagnosis (step 1) and three days after the treatment (step 2). At step 1, group 1 and group 2 were compared for thiol–disulfide homeostasis as well as inflammatory markers. At step 2, the same laboratory tests were repeated only in group 1. Results At step 1, the levels of C-reactive protein (CRP) and interleukin-6 (IL-6) were higher, while native thiol and total thiol levels were lower in group 1 compared to controls. Serum disulfide/total thiol ratio was also significantly higher in group 1. When analyzed for subgroups of group 1, demonstration of microorganism did not affect the serum thiol levels. Within group 1, at step 2, although CRP and IL-6 levels were significantly lowered compared to step 1, we did not observe significant changes in thiol–disulfide parameters. Conclusions The thiol–disulfide homeostasis may have a role in the pathogenesis of sepsis in newborns. The related parameters might be new markers for the diagnosis of sepsis in newborn patients. Further studies are needed to define the role of thiol–disulfide homeostasis in the course of neonatal sepsis.

Increased thiol levels in antimony-resistant Leishmania infantum isolated from treatment-refractory visceral leishmaniasis in Brazil.

BACKGROUNDTreatment-refractory visceral leishmaniasis (VL) has become an important problem in many countries.OBJECTIVESWe evaluated the antimony-resistance mechanisms of Leishmania infantum isolated from VL patients refractory or responsive to treatment with pentavalent antimony.METHODSStrains isolated from antimony-refractory patients (in vitro antimony-resistant isolates) and antimony-responsive patients (in vitro antimony-sensitive isolates) were examined. Morphological changes were evaluated by transmission electron microscopy after trivalent antimony exposure. P-glycoprotein (P-gp) efflux pump activity was evaluated using the pump-specific inhibitor verapamil hydrochloride, and the role of thiol in trivalent antimony resistance was investigated using the enzymatic inhibitor L-buthionine sulfoximine.FINDINGSAntimony treatment induced fewer alterations in the cellular structure of L. infantum resistant isolates than in that of sensitive isolates. P-gp efflux activity was not involved in antimony resistance in these isolates. Importantly, the resistant isolates contained higher levels of thiol compared to the sensitive isolates, and inhibition of thiol synthesis in the resistant isolates recovered their sensitivity to trivalent antimony treatment, and enhanced the production of reactive oxygen species in promastigotes exposed to the drug.MAIN CONCLUSIONSOur results demonstrate that isolates from patients with antimony-refractory VL exhibited higher thiol levels than antimony-sensitive isolates. This indicates that redox metabolism plays an important role in the antimony-resistance of New World VL isolates.

Kinetic characteristics of the reaction of resveratrol with peroxyl radicals and natural thiols in aqueous medium

The method of competing reactions was used to determine the rate constants of the reaction of resveratrol (RVT) with peroxyl radicals formed on decomposition of the azoinitiator ААРН in aqueous solutions at 37 °С. The polymethine dye A (3,3′-di-γ-sulfopropyl-9-metylthiacarbocyanine-betaine pyridinium salt) was used as a competing acceptor of radicals. It was found that resveratrol can be involved in the reaction with natural thiols, glutathione (GSH) and cysteine (CSH), in aqueous solutions at 37 °С. The reaction of RVT with thiols (thiol—еne reaction) follows a chain mechanism and accelerates in the presence of Н2О2. The results obtained can be useful for understanding the physiological role of thiols in oxidation processes.

Effect of l-Cysteine and Transition Metal Ions on Dimethyl Sulfide Oxidation.

During malt kilning, significant amounts of dimethyl sulfide (DMS) oxidize leading to the formation of dimethyl sulfoxide (DMSO), a precursor of DMS during fermentation. Yet, knowledge regarding reaction mechanisms of DMSO formation during malt production is limited. The role of thiols in sulfide oxidation is unclear as they possess sulfoxide reducing ability as well as pro- and antioxidative properties. This study investigated the effects of the thiol l-cysteine (Cys), molecular oxygen, transition metal ions, and EDTA on DMS oxidation in aqueous model solutions. Highest oxidative DMS consumption was observed when Cys was combined with iron(II) (∼12%) and copper(II) (∼40%). Response surface modeling (RSM) revealed that Cys together with copper(II) had a strictly prooxidative effect and no antioxidative behavior was found. Hydrogen peroxide, as generated via autoxidation of Cys-Cu(I)-Cys complexes, was supposed to be the primary DMS oxidant in this work. Based on redox kinetics, potential reaction mechanisms, and their impact on oxidative processes in thermal food processing, such as malt and beer production, are discussed.

Synthesis of a novel poly-thiolated magnetic nano-platform for heavy metal adsorption. Role of thiol and carboxyl functions

We report a novel strategy for the synthesis of magnetic nano-platforms containing free thiol groups. It first involves the synthesis of a poly(acrylic acid) copolymer containing disulfide bridges between the linear chains through di-ester linkages, followed by the anchoring of this new ligand to magnetite nanoparticles using a ligand exchange reaction. Finally, free SH groups are obtained by treating the resulting disulfide-functionalized magnetic nano-system with tributyl phosphine as reducing agent. The characterization of the resulting 17nm nanoparticles (Fe3O4@PAA-HEDred) by FTIR and TGA confirms the attachment of the copolymer through iron carboxylates. XRD, TEM and magnetic measurements indicate an increase in the inorganic core diameter and the occurrence of strong magnetic inter-particle interactions during the exchange reaction, although coercitivity and remanence drop to near zero at room temperature. Afterwards, Fe3O4@PAA-HEDred nanoparticles were tested as sorbent for Pb2+ and Cd2+ cations in aqueous media. XPS measurements were performed in order to unravel the role of both carboxyl and thiol functions in the adsorption process. For the sake of comparison, the same study was performed using bare Fe3O4 nanoparticles and a nanosystem with disulfide groups (Fe3O4@DMSA). The joint analysis of the Pb 4f, Cd 3d, Fe 2p and S 2p high resolution spectra for the nanostructured materials indicates that metal-sulfur interactions are dominant if free SH groups are present, but if not, the main adsorption route entails metal-carboxyl interactions. Even in presence of unbound thiol moieties, carboxyl groups participate due to favoured steric availability.

Phytotoxicity and detoxification mechanism differ among inorganic and methylated arsenic species in Arabidopsis thaliana

Plants are able to take up inorganic arsenic (As) and methylated As, but whether the mode of phytotoxicity and the detoxification mechanism differ between different As species remains unclear. This study aimed to investigate the differences in phytotoxicity and detoxification mechanism between arsenate [As(V)], monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)]. Arabidopsis thaliana was grown in agar-solidified medium, hydroponic or soil pot experiments. Root and shoot growth, seed production, As accumulation and oxidative stress indicators of wild-type plants exposed to As(V), MMA(V) and DMA(V) were compared. The role of thiols in As detoxification was investigated using a specific inhibitor of glutathione (GSH) biosynthesis and the mutants defective in GSH synthesis (cad2-1), phytochelatin (PC) synthesis (cad1-3) or tonoplast transporters for As(III)-PCs (abcc1-2). Methylated As species, especially DMA(V), were more toxic than As(V) for growth and seed production in A. thaliana. Methylated As species were more efficiently translocated from roots to shoots and from shoots to seeds than As(V). DMA(V) exposure resulted in a greater oxidative stress than other As species. As(V) and MMA(V) induced the production of non-protein thiols (NPT), but DMA(V) did not. The GSH inhibitor BSO greatly enhanced the sensitivity to As(V) and MMA(V), but decreased the sensitivity to DMA(V). The mutants cad1-3, cad2-1 and abcc1-2 were similarly hypersensitive to As(V) and MMA(V), but not to DMA(V). As(V) and MMA(V) enhanced the expression of the sulphur assimilation genes encoding ATP Sulphurylase (ATPS) and adenosine-5′-phosphosulphate reductase (APR1) more than DMA(V). DMA(V) is more toxic to A. thaliana than As(V) or MMA(V). The detoxification mechanism for MMA(V) is similar to that for As(V), involving thiol production, complexation with PCs and vacuolar sequestration. This mechanism is ineffective for the detoxification of DMA(V).

Solvent Influence on the Role of Thiols in Growth of Thiols-Capped Au Nanocrystals

Solvent has a key role in the controllable synthesis of nanocrystals (NCs). Here, using X-ray absorption spectroscopy, we demonstrate that solvent can significantly influence the adsorption of thiols on Au NCs, and thereby affects their growth. It is shown that increasing the solvent polarities leads to the higher thiol coverage on the NC surface. The high coverage of thiols then retards the growth of particles, and as a result, the NCs’ sizes decrease with the increase in the solvents’ polarities. The underlying reason for the solvent dependence is proposed to be the synergistic effects of different hydrogen bond and hydrophobic interactions between the sulfhydryl and alkyl groups of thiols with the solvents molecules. This work addresses the important role of the solvent environments in the size-controlled synthesis of NCs.

Role for plant peroxiredoxin in cadmium chelation

Studies on heavy metal underline the role of thiols in plants and attribute tolerance to metal binding. The thiol and peroxiredoxins (Prx) contents and guaiacol peroxidase (GPOX) activity were analyzed in the cotyledons and embryo of pea (Pisum sativum L.) germinating seeds exposed to toxic Cd concentration. The 2-cysteine peroxiredoxin (2Cys-Prx) level as well as the non-protein thiol (–SHNP) pool increased in both tissues treated with Cd compared to the control. An oxidized dimer of 2Cys-Prx was resolved in the presence of Cd ions. The obtained results suggest that Prx constitute a main key target in Cd toxicity. Despite of the decrease in GPOX activity due to the generation of an intracellular oxidative stress, a protective action via increasing Prx expression on thiols is possible to improve the redox status.

The Role of Thiol on Degradation of Pentaerythrityl Tetranitrate and Isosorbide Dinitrate

The Role of Thiol on Degradation of Pentaerythrityl Tetranitrate and Isosorbide Dinitrate

Role of glutathione in immunity and inflammation in the lung

Reactive oxygen species and thiol antioxidants, including glutathione (GSH), regulate innate immunity at various levels. This review outlines the redox-sensitive steps of the cellular mechanisms implicated in inflammation and host defense against infection, and describes how GSH is not only important as an antioxidant but also as a signaling molecule. There is an extensive literature of the role of GSH in immunity. Most reviews are biased by an oversimplified picture where “bad” free radicals cause all sorts of diseases and “good” antioxidants protect from them and prevent oxidative stress. While this may be the case in certain fields (eg, toxicology), the role of thiols (the topic of this review) in immunity certainly requires wearing scientist’s goggles and being prepared to accept a more complex picture. This review aims at describing the role of GSH in the lung in the context of immunity and inflammation. The first part summarizes the history and basic concepts of this picture. The second part focuses on GSH metabolism/levels in pathology, the third on the role of GSH in innate immunity and inflammation, and the fourth gives 4 examples describing the importance of GSH in the response to infections.

Long-term chromate reduction by immobilized fungus in continuous column

The immobilized fungus Coriolus versicolor was examined in a continuous fixed bed column for long-term Cr(VI) reduction at its physiological pH. The effects of operating parameters like flow rate, glucose concentration in the influent feed, COD, initial Cr(VI) concentration on the Cr(VI) reduction were investigated. Increase in the inlet Cr(VI) concentration and flow rate through the column led to a higher breakthrough of the Cr(VI) ions in the effluent. Cr(VI) reduction rate increased with increase in initial Cr(VI) concentration of up to 60 mg/L and thereafter showed a gradual decline. A Fourier transform infrared spectra were employed to elucidate the possible biosorption mechanism as well. The readiness of the thiol group of the fungal protein to interact with the Cr(VI) ion in addition to its strong reducing ability makes it a particularly important entity in the metabolism of Cr(VI). The possible role of thiol in the Cr(VI) reduction via the formation of Cr(VI) thioester is discussed. The study clearly exhibits the usage of live fungus for the long-term continuous removal of Cr(VI) as well as recovery of the metal ions from wastewater.

Toxicology of alkylmercury compounds.

Methylmercury is a global pollutant and potent neurotoxin whose abundance in the food chain mandates additional studies on the consequences and mechanisms of its toxicity to the central nervous system. Formulation of our new hypotheses was predicated on our appreciation for (a) the remarkable affinity of mercurials for the anionic form of sulfhydryl (-SH) groups, and (b) the essential role of thiols in protein biochemistry. The present chapter addresses pathways to human exposure of various mercury compounds, highlighting their neurotoxicity and potential involvement in neurotoxic injury and neurodegenerative changes, both in the developing and senescent brain. Mechanisms that trigger these effects are discussed in detail.

The Role of Thiols and Disulfides on Protein Stability

There has been a tremendous increase in the number of approved drugs derived from recombinant proteins; however, their development as potential drugs has been hampered by their instability that causes difficulty to formulate them as therapeutic agents. It has been shown that the reactivity of thiol and disulfide functional groups could catalyze chemical (i.e., oxidation and beta-elimination reactions) and physical (i.e., aggregation and precipitation) degradations of proteins. Because most proteins contain a free Cys residue or/and a disulfide bond, this review is focused on their roles in the physical and chemical stability of proteins. The effect of introducing a disulfide bond to improve physical stability of proteins and the mechanisms of degradation of disulfide bond were discussed. The qualitative/quantitative methods to determine the presence of thiol in the Cys residue and various methods to derivatize thiol group for improving protein stability were also illustrated.

The Role of Thiols on Sclerotial Differentiation of Filamentous Phytopathogenic Fungi

Sclerotial differentiation in filamentous phytopathogenic fungi, represented by four main types of sclerotia, was studied in relation to thiol redox state (TRS) by the TRS modulators glutathione (GSH), N-acetylcysteine (AcCSH, a cysteine (CSH) source and a GSH biosynthesis inducer), and dithiothreitol (DTT, a non specific antioxidant -SH group provider). It was shown that GSH and AcCSH increased either GSH or CSH or both during transition from the undifferentiated to the differentiated state, and, together with DTT, they inhibited sclerotial differentiation. Given the fact that the control thiol DTT had an analogous effect on the unrelated to sclerotial differentiation GSH and CSH levels, these data suggest that the decrease of sclerotial differentiation is related to the antioxidant action of -SH groups and not particularly to GSH and CSH.

CHARACTERIZATION OF NATURAL ANTIMONY RESISTANCE IN LEISHMANIA DONOVANI ISOLATES

Clinical resistance to pentavalent antimonial compounds has long been recognized as a major problem in the treatment of visceral leishmaniasis in India. However, mechanisms of natural resistance are unclear. In this study, we observed that Leishmania donovani clinical isolates not responsive to sodium stibogluconate showed resistance to antimony treatment in both in vitro and in vivo laboratory conditions. The resistant isolates have increased levels of intracellular thiols. This increase in thiol levels was not mediated by the amplification of gamma-glutamylcysteine synthetase, but was accompanied by amplification of trypanothione reductase and an intracellular ATP-binding cassette transporter gene MRPA. The resistance of parasites to antimony could be reversed by the glutathione biosynthesis-specific inhibitor, buthionine sulfoximine, which resulted in increased drug susceptibility. These results suggest the possible role of thiols and MRPA in antimony resistance in field isolates.

The Role of Thiols in Liver Ischemia-Reperfusion Injury

Thiol-containing compounds have an essential role in many biochemical reactions due to their ability to be easily oxidised and then quickly regenerated. Main representatives are glutathione, lipoic acid and thioredoxin which are synthesised de novo in mammalian cells. N-acetylcysteine and Bucillamine are synthetic thiols which have been administered in experimental and clinical studies for treatment of conditions associated with oxidative stress. Ischemia and reperfusion (I/R) injury is characterised by significant oxidative stress, characteristic changes in the antioxidant system and organ injury leading to significant morbidity and mortality. I/R occurs in a variety of clinical settings such as liver resection, organ transplantation, haemorrhagic shock with fluid resuscitation, heart surgery, myocardial infarction followed by reperfusion and laparoscopic surgery. In these circumstances, the administration of antioxidant agents such as thiols, could provide protection from the harmful effects of I/R injury. However, the ability of thiol compounds to reduce free radicals is associated with the formation of thiyl radicals and the rate and efficiency of removal of thiyl radicals has a critical effect on antioxidant or prooxidant actions of thiols in the cells. The aim of this review is to present the mechanisms by which thiols act as antioxidants and signalling molecules and the experimental and clinical evidence regarding their role in I/R injury with a particular emphasis on liver I/R. The current evidence suggests that thiols ameliorate I/R injury and that their clinical significance should be further evaluated in large scale randomised clinical trials.

Inhibition of jack bean urease by p-benzoquinone: elucidation of the role of thiols and reversibility of the process

p-Benzoquinone (pBQ) was studied as an inhibitor of jack bean urease in 20 mM phosphate buffer, pH 7.0, 1 mM EDTA, 25 °C. The inhibition was carried out by the use of a preincubation procedure in the absence of substrate. The influence of the inhibitor concentration and the preincubation time on the enzyme activity was elucidated. It was found that increase in pBQ concentration resulted in a linear decrease of urease activity. The dependence of the enzyme activity on the preincubation time showed that the rate of inhibition rapidly decreased at the beginning of the process in order to achieve the constant value. The inhibition became time independent in the studied time range. This observation is characteristic of a slow binding mechanism of inhibition. The protective experiment proved that the urease active site is involved in the binding of pBQ. High effectiveness of thiol protectors against pBQ inhibition indicates the strategic role of the active site sulfhydryl group in the blocking process. There were two methods used for reactivation of pBQ-inhibited urease. The dilution of the urease-pBQ complex in urea solution did not result in a regain of enzyme activity. Alternatively, the addition of dithiothreitol into the urease-pBQ mixture caused the instant and efficient reactivation of the enzyme. The experiments showed that the nature of the urease-pBQ complex is irreversible but the application of a specific thiol reagent can release the active enzyme from the complex.