Enzyme Kinetic Data Research Articles

Computational and experimental validation of morin as adenosine deaminase inhibitor

Adenosine deaminase (ADA) is one of the major enzymes involved in purin metabolism, it has a significant role in cell growth and differentiation. Over-activity of ADA has been noticed in some pathology, like malignancy and inflammation and makes it an attractive target for the development of drugs for such diseases. In the present study, ADA inhibitory activity of morin, a bioactive flavonoid, was assessed through computational and biophysical methods. The enzyme kinetics data showed that morin is a competitive inhibitor of ADA. Binding energy calculated from ITC analysis was −7.11 kcal/mol. Interaction of morin with ADA was also studied using fluorescence quenching method. Molecular docking studies revealed the structural details of the interaction. Molecular dynamics study in explicit solvent was also conducted to assess the structural stability of protein ligand complex.

STRENDA DB: enabling the validation and sharing of enzyme kinetics data.

Standards for reporting enzymology data (STRENDA) DB is a validation and storage system for enzyme function data that incorporates the STRENDA Guidelines. It provides authors who are preparing a manuscript with a user-friendly, web-based service that checks automatically enzymology data sets entered in the submission form that they are complete and valid before they are submitted as part of a publication to a journal.

N-Acetylmuramic Acid (MurNAc) Auxotrophy of the Oral Pathogen Tannerella forsythia: Characterization of a MurNAc Kinase and Analysis of Its Role in Cell Wall Metabolism.

Tannerella forsythia is an anaerobic, Gram-negative oral pathogen that thrives in multispecies gingival biofilms associated with periodontitis. The bacterium is auxotrophic for the commonly essential bacterial cell wall sugar N-acetylmuramic acid (MurNAc) and, thus, strictly depends on an exogenous supply of MurNAc for growth and maintenance of cell morphology. A MurNAc transporter (Tf_MurT; Tanf_08375) and an ortholog of the Escherichia coli etherase MurQ (Tf_MurQ; Tanf_08385) converting MurNAc-6-phosphate to GlcNAc-6-phosphate were recently described for T. forsythia. In between the respective genes on the T. forsythia genome, a putative kinase gene is located. In this study, the putative kinase (Tf_MurK; Tanf_08380) was produced as a recombinant protein and biochemically characterized. Kinetic studies revealed Tf_MurK to be a 6-kinase with stringent substrate specificity for MurNAc exhibiting a 6 × 104-fold higher catalytic efficiency (kcat/Km) for MurNAc than for N-acetylglucosamine (GlcNAc) with kcat values of 10.5 s-1 and 0.1 s-1 and Km values of 200 μM and 116 mM, respectively. The enzyme kinetic data suggest that Tf_MurK is subject to substrate inhibition (Ki[S] = 4.2 mM). To assess the role of Tf_MurK in the cell wall metabolism of T. forsythia, a kinase deletion mutant (ΔTf_murK::erm) was constructed. This mutant accumulated MurNAc intracellularly in the exponential phase, indicating the capability to take up MurNAc, but inability to catabolize MurNAc. In the stationary phase, the MurNAc level was reduced in the mutant, while the level of the peptidoglycan precursor UDP-MurNAc-pentapeptide was highly elevated. Further, according to scanning electron microscopy evidence, the ΔTf_murK::erm mutant was more tolerant toward low MurNAc concentration in the medium (below 0.5 μg/ml) before transition from healthy, rod-shaped to fusiform cells occurred, while the parent strain required > 1 μg/ml MurNAc for optimal growth. These data reveal that T. forsythia readily catabolizes exogenous MurNAc but simultaneously channels a proportion of the sugar into peptidoglycan biosynthesis. Deletion of Tf_murK blocks MurNAc catabolism and allows the direction of MurNAc solely to peptidoglycan biosynthesis, resulting in a growth advantage in MurNAc-depleted medium. This work increases our understanding of the T. forsythia cell wall metabolism and may pave new routes for lead finding in the treatment of periodontitis.

Structural insights into drug development strategy targeting EGFR T790M/C797S.

Treatment of non-small-cell lung cancers (NSCLCs) harboring primary EGFR oncogenic mutations such as L858R and exon 19 deletion delE746_A750 (Del-19) using gefitinib/erlotinib ultimately fails due to the emergence of T790M mutation. Though WZ4002/CO-1686/AZD9291 are effective in overcoming EGFR T790M by targeting Cys797 via covalent bonding, their efficacy is again limited due to the emergence of C797S mutation. New agents effectively inhibiting EGFR T790M without covalent linkage through Cys 797 may solve this problem. We presented here crystal structures of EGFR activating/drug-resistant mutants in complex with a panel of reversible inhibitors along with mutagenesis and enzyme kinetic data. These data revealed a previously un-described hydrophobic clamp structure in the EGFR kinase which may be exploited to facilitate development of next generation drugs targeting EGFR T790M with or without concomitant C797S. Interestingly, mutations in the hydrophobic clamp that hinder drug binding often also weaken ATP binding and/or abolish kinase activity, thus do not readily result in resistance to the drugs.

Free Heme and Amyloid-β: A Fatal Liaison in Alzheimer's Disease.

While the etiology of Alzheimer's disease (AD) is still unknown, an increased formation of amyloid-β (Aβ) peptide and oxidative processes are major pathological mechanism of the disease. The interaction of Aβ with free heme leads to the formation of peroxidase-active Aβ-heme complexes. However, enzyme-kinetic data and systematic mutational studies are still missing. These aspects were addressed in this study to evaluate the role of Aβ-heme complexes in AD. The enzyme-kinetic measurements showed peroxidase-specific pH- and H2O2-dependencies. In addition, the enzymatic activity of Aβ-heme complexes constantly increased at higher peptide excess. Moreover, the role of the Aβ sequence for the named enzymatic activity was tested, depicting human-specific R5, Y10, and H13 as essential amino acids. Also by studying Y10 as an endogenous peroxidase substrate for Aβ-heme complexes, ratio-specific effects were observed, showing an optimal dityrosine formation at an about 40-fold peptide excess. As dityrosine formation promotes Aβ fibrillation while free heme disturbs protein aggregation, we also investigated the effect of Aβ-heme complex-derived peroxidase activity on the formation of Aβ fibrils. The fluorescence measurements showed a different fibrillation behavior at strong peroxidase activity, leading also to altered fibril morphologies. The latter was detected by electron microscopy. As illustrated by selected in vivo measurements on a mouse model of AD, the disease is also characterized by Aβ-derived microvessel destructions and hemolytic processes. Thus, thrombo-hemorrhagic events are discussed as a source for free heme in brain tissue. In summary, we suggest the formation and enzymatic activity of Aβ-heme complexes as pathological key features of AD.

Cloning, expression and characterization of two S-ribosylhomocysteine lyases from Lactobacillus plantarum YM-4-3: Implication of conserved and divergent roles in quorum sensing

Quorum sensing (QS) is a means of cell-to-cell communication that regulates, via small signalling molecules, expression of a series of genes and controls multicellular behaviour in many bacterial species. The enzyme S-ribosylhomocysteine lyase (LuxS) transforms S-ribosylhomocysteine (SRH) into 4, 5-dihydroxy-2, 3-pentanedione (DPD), the precursor of the interspecies QS signalling molecule autoinducer-2 (AI-2). In this study, two LuxS-coding genes, luxS1 and luxS2, with 70% sequence identity were isolated from Lactobacillus plantarum YM-4-3, and overexpressed in Escherichia coli BL21 (DE3), and the protein products were purified successfully. After incubation of LuxS1 or LuxS2 with SRH, the reaction products were able to induce Vibrio harveyi BB170 bioluminescence, clearly demonstrating that both LuxS1 and LuxS2 synthesize AI-2 from SRH in vitro. Ellman's assay results revealed optimal temperatures for LuxS1 and LuxS2 of 45 and 37 °C, respectively, and their activities were stimulated or inhibited by several metal ions and chemical reagents. In addition, enzyme kinetics data showed that Km, Vmax and Kcat value of LuxS1 for the substrate (SRH) were higher than that of LuxS2. These results suggest that LuxS1 and LuxS2 mediate QS in a temperature-dependent manner and may play conserved roles in AI-2 synthesis but exhibit different activities in response to external environmental stress. To our knowledge, this paper is the first report of two luxS genes present in one bacterial genome and the subsequent comparative elucidation of their functions in AI-2 production. Collectively, our study provides a solid basis for future research concerning the AI-2/LuxS QS system in L. plantarum YM-4-3.

Can you trust the parametric standard errors in nonlinear least squares? Yes, with provisos

BackgroundQuestions about the reliability of parametric standard errors (SEs) from nonlinear least squares (LS) algorithms have led to a general mistrust of these precision estimators that is often unwarranted. MethodsThe importance of non-Gaussian parameter distributions is illustrated by converting linear models to nonlinear by substituting eA, ln A, and 1/A for a linear parameter a. Monte Carlo (MC) simulations characterize parameter distributions in more complex cases, including when data have varying uncertainty and should be weighted, but weights are neglected. This situation leads to loss of precision and erroneous parametric SEs, as is illustrated for the Lineweaver-Burk analysis of enzyme kinetics data and the analysis of isothermal titration calorimetry data. ResultsNon-Gaussian parameter distributions are generally asymmetric and biased. However, when the parametric SE is <10% of the magnitude of the parameter, both the bias and the asymmetry can usually be ignored. Sometimes nonlinear estimators can be redefined to give more normal distributions and better convergence properties. ConclusionVariable data uncertainty, or heteroscedasticity, can sometimes be handled by data transforms but more generally requires weighted LS, which in turn require knowledge of the data variance. General significanceParametric SEs are rigorously correct in linear LS under the usual assumptions, and are a trustworthy approximation in nonlinear LS provided they are sufficiently small — a condition favored by the abundant, precise data routinely collected in many modern instrumental methods.

Peroxidase inactivation kinetics is affected by the addition of calcium chloride in fruit beverages

The effect of calcium chloride addition on the peroxidase (POD) thermal inactivation was evaluated in a fruit juice model solution and coconut water. The evaluation was conducted over the temperature range from 63 to 85 °C, considering the non-isothermal profile of processing. The accumulated lethality was calculated and the obtained data were well described by the first order kinetic model. The presence of calcium chloride resulted in an increase of POD thermal stabilities in both fruit juice model solution and green coconut water, being the inactivation kinetics also affected. Although all enzyme kinetics data of fruit juice solution can be described by the first order kinetic model, their response to thermal processing were different depending on the concentration of calcium chloride. The obtained results highlight the importance of evaluating engineering aspects of food formulation, as ingredients applied for nutritional or sensorial aspects can also impact the process performance.

Structural enzymology comparisons of multifunctional enzyme, type-1 (MFE1): the flexibility of its dehydrogenase part.

Multifunctional enzyme, type‐1 (MFE1) is a monomeric enzyme with a 2E‐enoyl‐CoA hydratase and a 3S‐hydroxyacyl‐CoA dehydrogenase (HAD) active site. Enzyme kinetic data of rat peroxisomal MFE1 show that the catalytic efficiencies for converting the short‐chain substrate 2E‐butenoyl‐CoA into acetoacetyl‐CoA are much lower when compared with those of the homologous monofunctional enzymes. The mode of binding of acetoacetyl‐CoA (to the hydratase active site) and the very similar mode of binding of NAD + and NADH (to the HAD part) are described and compared with those of their monofunctional counterparts. Structural comparisons suggest that the conformational flexibility of the HAD and hydratase parts of MFE1 are correlated. The possible importance of the conformational flexibility of MFE1 for its biocatalytic properties is discussed.DatabaseStructural data are available in PDB database under the accession number 5MGB.

In Vivo and In Vitro Evidence for the Antihyperuricemic, Anti-inflammatory and Antioxidant Effects of a Traditional Ayurvedic Medicine, Triphala

The objectives of the present study were to demonstrate the antihyperuricemic effect of triphala, a formulation of traditional Ayurvedic medicine, in potassium oxonate-induced hyperuricemic mice in vivo, and to examine its inhibitor effects on xanthine oxidase (XOD), inflammatory mediators and DPPH radicals in vitro. The water extract of triphala was determined to contain the total phenolics and total flavonoids of 317.6 ± 9.2 mg GAE/g and 7.73 ± 0.26 mg QE/g, respectively. Oral administrations of triphala significantly reduced the plasma uric acid levels of potassium oxonate-induced hyperuricemic mice at doses of 1,000 and 1,500 mg/kg, as compared with control ( p&lt;0.05). Moreover, both doses of triphala treatments markedly inhibited the formation of uric acid due to inhibition of XOD activity in liver homogenates extracted from the hyperuricemic mice by about 70-80%. Lineweaver-Burk analysis of enzyme-kinetic data showed that triphala exhibited non-competitive inhibition on XOD activity in vitro with an inhibitory constant (Ki) of 590 μg/mL. Furthermore, triphala significantly suppressed the mRNA expressions of COX-II, TNF-α and iNOS in LPS-stimulated RAW 264.7 cells, as compared with control ( p &lt;0.05), and decreased the expression of TGF-β. IC50 values for inhibition of DPPH radical formation was calculated to be 21.9 ± 2.50 μg/mL. Antioxidant activities of triphala were determined to be 0.81 ± 0.07 g TEAC/g and 6.78 ± 0.29 mmol/100g, respectively, as assessed by ABTS and FRAP assays. In conclusion, this study provided in vivo and in vitro mechanistic evidence for the antihyperuricemic, antioxidative and anti-inflammatory effects of triphala for the first time, rationalizing its therapeutic usage for the treatment of hyperuricemia of gout.

Structures of Leishmania Fructose-1,6-Bisphosphatase Reveal Species-Specific Differences in the Mechanism of Allosteric Inhibition

The gluconeogenic enzyme fructose-1,6-bisphosphatase has been proposed as a potential drug target against Leishmania parasites that cause up to 20,000–30,000 deaths annually. A comparison of three crystal structures of Leishmania major fructose-1,6-bisphosphatase (LmFBPase) along with enzyme kinetic data show how AMP acts as an allosteric inhibitor and provides insight into its metal-dependent reaction mechanism. The crystal structure of the apoenzyme form of LmFBPase is a homotetramer in which the dimer of dimers adopts a planar conformation with disordered “dynamic loops”. The structure of LmFBPase, complexed with manganese and its catalytic product phosphate, shows the dynamic loops locked into the active sites. A third crystal structure of LmFBPase complexed with its allosteric inhibitor AMP shows an inactive form of the tetramer, in which the dimer pairs are rotated by 18° relative to each other. The three structures suggest an allosteric mechanism in which AMP binding triggers a rearrangement of hydrogen bonds across the large and small interfaces. Retraction of the “effector loop” required for AMP binding releases the side chain of His23 from the dimer–dimer interface. This is coupled with a flip of the side chain of Arg48 which ties down the key catalytic dynamic loop in a disengaged conformation and also locks the tetramer in an inactive rotated T-state. The structure of the effector site of LmFBPase shows different structural features compared with human FBPases, thereby offering a potential and species-specific drug target.

Peroxo Compounds of Vanadium(V) and Niobium(V) as Potent Inhibitors of Calcineurin Activity towards RII‐Phosphopeptide

AbstractCalcineurin (CN) is a major calmodulin binding serine/threonine phosphatase which plays a crucial role in numerous mammalian signal transduction pathways. Calcineurin inhibitors represent a valuable tool for elucidating CN dependent cellular processes. The present work deals with the synthesis and comprehensive characterization of a new polymer anchored peroxo niobium complex, [Nb2(O2)6(carboxylate)2]‐PA (Nb2) [PA=poly(sodium acrylate)], and identification of a set comprising of neat homoleptic as well as polymer immobilized peroxo complexes of vanadium(V) and niobium(V) as potent CN inhibitors. The in‐vitro effect of the complexes on calmodulin mediated dephosphorylation activity of CN was investigated using a physiological substrate of calcineurin, RII‐phosphopeptide as well as a non‐protein substrate p‐nitrophenyl phosphate (p‐NPP). Enzyme kinetic analysis data revealed that the compounds inhibit function of CN via uncompetitive pathway with Ki values ranging between 1–3 μM, suggesting the formation of an enzyme‐inhibitor‐substrate complex during the course of inhibition.

Azomethines, isoxazole, N-substituted pyrazoles and pyrimidine containing curcumin derivatives: Urease inhibition and molecular modeling studies

Curcumin has shown large number of pharmacological properties against different phenotypes of various disease models. Different synthetic routes have been employed to develop its various derivatives for diverse biological functions. In this study, curcumin derived azomethine, isoxazole, pyrimidines and N-substituted pyrazoles were synthesized to investigate their urease enzyme inhibition. The structures of newly synthesized compounds were described by IR, MS, 1H NMR and 13C NMR spectral data. Urease enzyme inhibition was evaluated through in vitro assays in which compound 8b was found to be the most potent (IC50 = 2.44 ± 0.07 μM) among the tested compounds. The compounds with diazine ring system except the 4d showed better urease inhibition (IC50 = 11.43 ± 0.21–19.63 ± 0.28 μM) than the standard urease inhibitor thiourea (IC50 = 22.61 ± 0.23 μM). Similarly enzyme kinetics data revealed that compounds 3c-3e and 8b were competitive inhibitors with Ki values of 20.0, 19.87, 20.23 and 19.11 μM respectively while the compounds 4b, 4c and 4e were mixed type of inhibitors with Ki values 6.72, 19.69 and 6.72 μM respectively. Molecular docking studies were also performed to identify the plausible binding modes of the most active compounds.

The Enzyme Activity and Substrate Specificity of Two Major Cinnamyl Alcohol Dehydrogenases in Sorghum (Sorghum bicolor), SbCAD2 and SbCAD4.

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the final step in monolignol biosynthesis, reducing sinapaldehyde, coniferaldehyde, and p-coumaraldehyde to their corresponding alcohols in an NADPH-dependent manner. Because of its terminal location in monolignol biosynthesis, the variation in substrate specificity and activity of CAD can result in significant changes in overall composition and amount of lignin. Our in-depth characterization of two major CAD isoforms, SbCAD2 (Brown midrib 6 [bmr6]) and SbCAD4, in lignifying tissues of sorghum (Sorghum bicolor), a strategic plant for generating renewable chemicals and fuels, indicates their similarity in both structure and activity to Arabidopsis (Arabidopsis thaliana) CAD5 and Populus tremuloides sinapyl alcohol dehydrogenase, respectively. This first crystal structure of a monocot CAD combined with enzyme kinetic data and a catalytic model supported by site-directed mutagenesis allows full comparison with dicot CADs and elucidates the potential signature sequence for their substrate specificity and activity. The L119W/G301F-SbCAD4 double mutant displayed its substrate preference in the order coniferaldehyde > p-coumaraldehyde > sinapaldehyde, with higher catalytic efficiency than that of both wild-type SbCAD4 and SbCAD2. As SbCAD4 is the only major CAD isoform in bmr6 mutants, replacing SbCAD4 with L119W/G301F-SbCAD4 in bmr6 plants could produce a phenotype that is more amenable to biomass processing.

Enzyme Kinetics Experiment with the Multienzyme Complex Viscozyme L and Two Substrates for the Accurate Determination of Michaelian Parameters

A laboratory experiment in which students study the kinetics of the Viscozyme-L-catalyzed hydrolysis of cellulose and starch comparatively was designed for an upper-division biochemistry laboratory. The main objective of this experiment was to provide an opportunity to perform enhanced enzyme kinetics data analysis using appropriate informatics and statistical tools. By fitting the Michaelis–Menten, Lineweaver–Burk, Eadie–Hofstee, and Hanes equations to the experimental data, students explore the strengths and weaknesses of each plot and determine whether the two Viscozyme-L-catalyzed reactions obey Michaelis–Menten kinetics. Comparing the values of the Michaelian constants (vmax and KM) and the efficiencies obtained for each enzyme-catalyzed reaction allows advanced undergraduates to determine if the differences between these parameters are statistically significant.

Structural pharmacological studies on EGFR T790M/C797S

Drug-resistance is a major challenge in targeted therapy of EGFR mutated non-small cell lung cancers (NSCLCs). The third-generation irreversible inhibitors such as AZD9291, CO-1686 and WZ4002 can overcome EGFR T790M drug-resistance mutant through covalent binding through Cys 797, but ultimately lose their efficacy upon emergence of the new mutation C797S. To develop new reversible inhibitors not relying on covalent binding through Cys 797 is therefore urgently demanded. Gö6976 is a staurosporine-like reversible inhibitor targeting T790M while sparing the wild-type EGFR. In the present work, we reported the complex crystal structures of EGFR T790M/C797S + Gö6976 and T790M + Gö6976, along with enzyme kinetic data of EGFR wild-type, T790M and T790M/C797S. These data showed that the C797S mutation does not significantly alter the structure and function of the EGFR kinase, but increases the local hydrophilicity around residue 797. The complex crystal structures also elucidated the detailed binding mode of Gö6976 to EGFR and explained why this compound prefers binding to T790M mutant. These structural pharmacological data would facilitate future drug development studies.

Simultaneous enzymatic activity modulation and rapid determination of enzyme kinetics by highly crystalline graphite dots.

The research field in enzyme-based biotechnology urgently requires the discovery of new materials and methods with high-performance. Here we report that highly crystalline graphite dots (GDs) can modulate enzyme activities, and simultaneously allow for real-time measurements on enzyme kinetics in combination with mass spectrometry (MS). A well-defined modulation of lipolytic activities from inhibition to enhancement can be realized by selectively coupling lipase enzymes with GDs containing specific functional groups on the surface. As a unique feature of our approach, GDs in the enzyme reaction can simultaneously serve as a versatile matrix for rapid and sensitive detection of the residual enzyme substrate, the intermediate or final product of lipolytic digestion using MS technology. Therefore, enzyme kinetic data can be collected in a real-time, high-throughput format. This work provides a new platform for enzymological research in hybrid bio-catalytic processes with advanced nanotechnology.

Effects of Glycosylation on the Enzymatic Activity and Mechanisms of Proteases.

Posttranslational modifications are an important feature of most proteases in higher organisms, such as the conversion of inactive zymogens into active proteases. To date, little information is available on the role of glycosylation and functional implications for secreted proteases. Besides a stabilizing effect and protection against proteolysis, several proteases show a significant influence of glycosylation on the catalytic activity. Glycans can alter the substrate recognition, the specificity and binding affinity, as well as the turnover rates. However, there is currently no known general pattern, since glycosylation can have both stimulating and inhibiting effects on activity. Thus, a comparative analysis of individual cases with sufficient enzyme kinetic and structural data is a first approach to describe mechanistic principles that govern the effects of glycosylation on the function of proteases. The understanding of glycan functions becomes highly significant in proteomic and glycomic studies, which demonstrated that cancer-associated proteases, such as kallikrein-related peptidase 3, exhibit strongly altered glycosylation patterns in pathological cases. Such findings can contribute to a variety of future biomedical applications.

Diethylalkylsulfonamido(4-methoxyphenyl)methyl)phosphonate/phosphonic acid derivatives act as acid phosphatase inhibitors: synthesis accompanied by experimental and molecular modeling assessments

Purple acid phosphatases (PAPs) are binuclear metallo-hydrolases that have been isolated from various mammals, plants, fungi and bacteria. In mammals, PAP activity is associated with bone resorption and can lead to bone metabolic disorders such as osteoporosis; thus human PAP is an attractive target to develop anti-osteoporotic drugs. The aim of the present study was to investigate inhibitory effect of synthesized diethylalkylsulfonamido(4-methoxyphenyl)methyl)phosphonate/phosphonic acid derivatives as potential red kidney bean PAP (rkbPAP) inhibitors accompanied by experimental and molecular modeling assessments. Enzyme kinetic data showed that they are good rkbPAP inhibitors whose potencies improve with increasing alkyl chain length. Hexadecyl derivatives, as most potent compounds (Ki = 1.1 µM), inhibit rkbPAP in the mixed manner, while dodecyl derivatives act as efficient noncompetitive inhibitor. Also, analysis by molecular modeling of the structure of the rkbPAP–inhibitor complexes reveals factors, which may be important for the determination of inhibition specificity.

Niobium(V) peroxo α-amino acid complexes: Synthesis, stability and kinetics of inhibition of acid phosphatase activity

The present work was undertaken with an objective to investigate some biologically relevant attributes of peroxoniobium (pNb) derivatives, using a set of heteroleptic pNb compounds containing biogenic species as co-ligands. New peroxoniobium complexes corresponding to the general formula, Na2[Nb(O2)3L] (L=alanine or valine) were synthesized and comprehensively characterized by elemental analysis, IR, Raman, 13C NMR, 1H NMR, AAS and UV–Vis spectral studies, as well as thermogravimetric analysis. The structures of the compounds have been studied by density functional theory (DFT) method and their stability in solution at physiological pH has been ascertained. These compounds, along with our previously reported arginine and nicotinate complexes, Na2[Nb(O2)3(arg)]·2H2O and Na2[Nb(O2)3(nic)(H2O)]·H2O, respectively were screened for their activities with two different types of enzymes viz., catalase and acid phosphatase (ACP). Employing wheat thylakoid ACP as the model enzyme, it has been demonstrated for the first time that peroxoniobium derivatives serve as active inhibitors of phosphatase (IC50 values 2–9μM). Enzyme kinetics data revealed that compounds exert mixed type of inhibition on ACP activity (Kii>Ki). Each of the tested pNb species exhibited significant resistance to degradation under the effect of catalase vis-a-vis the native substrate of the enzyme, H2O2.