Phosphoester Bond Hydrolysis Research Articles

Brazilin-Ce nanoparticles attenuate inflammation by de/anti-phosphorylation of IKKβ

Inflammation is associated with a series of diseases like cancer, cardiovascular disease and infection, and phosphorylation/dephosphorylation modification of proteins are important in inflammation regulation. Here we designed and synthesized a novel Brazilin-Ce nanoparticle (BX-Ce NPs) using Brazilin, which has been used for anti-inflammation in cardiovascular diseases but with narrow therapeutic window, and Cerium (IV), a lanthanide which has the general activity in catalyzing the hydrolysis of phosphoester bonds, to conferring de/anti-phosphorylation of IKKβ. We found that BX-Ce NPs specifically bound to Asn225 and Lys428 of IKKβ and inhibited its phosphorylation at Ser181, contributing to appreciably anti-inflammatory effect in cellulo (IC50 = 2.5 μM). In vivo mouse models of myocardial infarction and sepsis also showed that the BX-Ce NPs significantly ameliorated myocardial injury and improved survival in mice with experimental sepsis through downregulating phosphorylation of IKKβ. These findings provided insights for developing metal nanoparticles for guided ion interfere therapy, particularly synergistically target de/anti-phosphorylation as promising therapeutic agents for inflammation and related diseases.

Phosphoester bond hydrolysis by a discrete zirconium-oxo cluster: mechanistic insights into the central role of the binuclear ZrIV-ZrIV active site.

Effective degradation of non-natural phosphate triesters (PTs) widely used in pesticides and warfare agents is of paramount relevance for human and environmental safety, particularly under acidic conditions where they are highly stable. Here, we present a detailed reactivity and mechanistic study pioneering discrete {Zr6O8} clusters, which are commonly employed as building blocks for Zr-MOFs and as non-classical soluble coordination compounds for the degradation of PTs using the pesticide ethyl paraoxon as a model. Combined computational studies, mechanistic experiments, and EXAFS analysis show that the reactivity of these clusters arises from their ZrIV-ZrIV bimetallic sites, which hydrolyze ethyl paraoxon under acidic conditions through an intramolecular pathway. Remarkably, the energetics of the reaction is dependent on the protonation state of the active sites, and a weakly acidic medium favors the reaction. Moreover, catalyst stability allowed for its recovery and reuse. Such a mechanism is in close analogy to enzymatic reactions and different from that previously reported for Zr-MOFs. These findings outline the potential of MIV-MIV active sites for PT degradation under challenging aqueous acidic conditions and contribute to the development of bioinspired catalysts and materials.

Biodegradation pathway and mechanism of tri (2-chloropropyl) phosphate by Providencia rettgeri

Tri (2-chloropropyl) phosphate (TCPP) was an emerging contaminant of global concern because of its frequent occurrence, potential toxic effects, and persistence in the environment. Microbial degradation might be an efficient and safe removal method, but limited information was available. In this study, Providencia rettgeri was isolated from contaminated sediment and showed it could use TCPP as unique phosphorus source to promote growth, and decompose 34.7% of TCPP (1 mg/L) within 5 days. The microbial inoculation and the initial concentration of TCPP could affect the biodegradation efficient. Further study results indicated that TCPP decomposition by Providencia rettgeri was mainly via phosphoester bond hydrolysis, evidenced by the production of bis (2-chloropropyl) phosphate (C6H13Cl2PO4) and mono-chloropropyl phosphate (C3H8ClPO4). Both intracellular and extracellular enzymes could degrade TCPP, but intracellular degradation was dominant in the later reaction stage, and the presence of Cu2+ ions had a promoting effect. These findings developed novel insights into the potential mechanism of TCPP microbial degradation.

Meta-omics elucidates key degraders in a bacterial tris(2-butoxyethyl) phosphate (TBOEP)-degrading enrichment culture

Organophosphate esters (OPEs) are emerging contaminants of growing concern, and there is limited information about the bacterial transformation of OPEs. In this study, we investigated the biotransformation of tris(2-butoxyethyl) phosphate (TBOEP), a frequently detected alkyl-OPE by a bacterial enrichment culture under aerobic conditions. The enrichment culture degraded 5 mg/L TBOEP following the first-order kinetics with a reaction rate constant of 0.314 h−1. TBOEP was mainly degraded via ether bond cleavage, evidenced by the production of bis(2-butoxyethyl) hydroxyethyl phosphate, 2-butoxyethyl bis(2-hydroxyethyl) phosphate, and 2-butoxyethyl (2-hydroxyethyl) hydrogen phosphate. Other transformation pathways include terminal oxidation of the butoxyethyl group and phosphoester bond hydrolysis. Metagenomic sequencing generated 14 metagenome-assembled genomes (MAGs), showing that the enrichment culture primarily consisted of Gammaproteobacteria, Bacteroidota, Myxococcota, and Actinobacteriota. One MAG assigned to Rhodocuccus ruber strain C1 was the most active in the community, showing upregulation of various monooxygenase, dehydrogenase, and phosphoesterase genes throughout the degradation process, and thus was identified as the key degrader of TBOEP and the metabolites. Another MAG affiliated with Ottowia mainly contributed to TBOEP hydroxylation. Our results provided a comprehensive understanding of the bacterial TBOEP degradation at community level.

New Insights on the Interaction of Phenanthroline Based Ligands and Metal Complexes and Polyoxometalates with Duplex DNA and G-Quadruplexes.

This work provides new insights from our team regarding advances in targeting canonical and non-canonical nucleic acid structures. This modality of medical treatment is used as a form of molecular medicine specifically against the growth of cancer cells. Nevertheless, because of increasing concerns about bacterial antibiotic resistance, this medical strategy is also being explored in this field. Up to three strategies for the use of DNA as target have been studied in our research lines during the last few years: (1) the intercalation of phenanthroline derivatives with duplex DNA; (2) the interaction of metal complexes containing phenanthroline with G-quadruplexes; and (3) the activity of Mo polyoxometalates and other Mo-oxo species as artificial phosphoesterases to catalyze the hydrolysis of phosphoester bonds in DNA. We demonstrate some promising computational results concerning the favorable interaction of these small molecules with DNA that could correspond to cytotoxic effects against tumoral cells and microorganisms. Therefore, our results open the door for the pharmaceutical and medical applications of the compounds we propose.

Mechanistic Insights into Promoted Hydrolysis of Phosphoester Bonds by MoO2Cl2(DMF)2.

A phosphoester bond is a crucial structural block in biological systems, whose occurrence is regulated by phosphatases. Molybdenum compounds have been reported to be active in phosphate ester hydrolysis of model phosphates. Specifically, MoO2Cl2(DMF)2 is active in the hydrolysis of para-nitrophenyl phosphate (pNPP), leading to heteropolyoxometalate structures. We use density functional theory (DFT) to clarify the mechanism by which these species promote the hydrolysis of the phosphoester bond. The present calculations give insight into several key aspects of this reaction: (i) the speciation of this complex prior to interaction with the phosphate (DMF release, Mo-Cl hydrolysis, and pH influence on the speciation), (ii) the competition between phosphate addition and the molybdate nucleation process, (iii) and the mechanisms by which some plausible active species promote this hydrolysis in different conditions. We described thoroughly two different pathways depending on the nucleation possibilities of the molybdenum complex: one mononuclear mechanism, which is preferred in conditions in which very low complex concentrations are used, and another dinuclear mechanism, which is preferred at higher concentrations.

Crystal structures of SAMHD1 inhibitor complexes reveal the mechanism of water-mediated dNTP hydrolysis

SAMHD1 regulates cellular 2′-deoxynucleoside-5′-triphosphate (dNTP) homeostasis by catalysing the hydrolysis of dNTPs into 2′-deoxynucleosides and triphosphate. In CD4+ myeloid lineage and resting T-cells, SAMHD1 blocks HIV-1 and other viral infections by depletion of the dNTP pool to a level that cannot support replication. SAMHD1 mutations are associated with the autoimmune disease Aicardi–Goutières syndrome and hypermutated cancers. Furthermore, SAMHD1 sensitises cancer cells to nucleoside-analogue anti-cancer therapies and is linked with DNA repair and suppression of the interferon response to cytosolic nucleic acids. Nevertheless, despite its requirement in these processes, the fundamental mechanism of SAMHD1-catalysed dNTP hydrolysis remained unknown. Here, we present structural and enzymological data showing that SAMHD1 utilises an active site, bi-metallic iron-magnesium centre that positions a hydroxide nucleophile in-line with the Pα-O5′ bond to catalyse phosphoester bond hydrolysis. This precise molecular mechanism for SAMHD1 catalysis, reveals how SAMHD1 down-regulates cellular dNTP and modulates the efficacy of nucleoside-based anti-cancer and anti-viral therapies.

Biotransformation of Tris(2-chloroethyl) Phosphate (TCEP) in Sediment Microcosms and the Adaptation of Microbial Communities to TCEP

Tris(2-chloroethyl) phosphate (TCEP), a typical chlorinated organophosphate ester (OPE), is an emerging contaminant of global concern because of its frequent occurrence, potential toxic effects, and persistence in the environment. In this study, we investigated the microbial TCEP biotransformation and the development of microbial communities in sediment microcosms with repeated TCEP amendments. The TCEP degradation fitted pseudo-zero-order kinetics, with reaction rates of 0.068 mg/(L h) after the first spike of 5 mg/L and 1.85 mg/(L h) after the second spike of 50 mg/L. TCEP was mainly degraded via phosphoester bond hydrolysis, evidenced by the production of bis(2-chloroethyl) phosphate (BCEP) and mono-chloroethyl phosphate (MCEP). Bis(2-chloroethyl) 2-hydroxyethyl phosphate (TCEP-OH), phosphoric bis(2-chloroethyl) (2-oxoethyl) ester (TCEP-CHO), phosphoric acid bis(2-chloroethyl)(carboxymethyl) ester (TCEP-COOH), and 2-chloroethyl 2-hydroxyethyl hydrogen phosphate (BCEP-OH) were also identified as microbial TCEP transformation products, indicating that TCEP degradation may follow hydrolytic dechlorination and oxidation pathways. Microbial community compositions in TCEP-amended microcosms shifted away from control microcosms after the second TCEP spike. Burkholderiales and Rhizobiales were two prevalent bacterial guilds enriched in TCEP-amended microcosms and were linked to the higher abundances of alkaline and acid phosphatase genes and genes involved in the metabolism of 2-chloroethanol, a side product of TCEP hydrolysis, indicating their importance in degrading TCEP and its metabolites.

Multinuclear diffusion NMR spectroscopy and DFT modeling: a powerful combination for unraveling the mechanism of phosphoester bond hydrolysis catalyzed by metal-substituted polyoxometalates.

A detailed reaction mechanism is proposed for the hydrolysis of the phosphoester bonds in the DNA model substrate bis(4-nitrophenyl) phosphate (BNPP) in the presence of the Zr(IV)-substituted Keggin type polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]⋅7 H2O (ZrK 2:2) at pD 6.4. Low-temperature (31)P DOSY spectra at pD 6.4 gave the first experimental evidence for the presence of ZrK 1:1 in fast equilibrium with ZrK 2:2 in purely aqueous solution. Moreover, theoretical calculations identified the ZrK 1:1 form as the potentially active species in solution. The reaction intermediates involved in the hydrolysis were identified by means of (1)H/(31)P NMR studies, including EXSY and DOSY NMR spectroscopy, which were supported by DFT calculations. This experimental/theoretical approach enabled the determination of the structures of four intermediate species in which the starting compound BNPP, nitrophenyl phosphate (NPP), or the end product phosphate (P) is coordinated to ZrK 1:1. In the proposed reaction mechanism, BNPP initially coordinates to ZrK 1:1 in a monodentate fashion, which results in hydrolysis of the first phosphoester bond in BNPP and formation of NPP. EXSY NMR studies showed that the bidentate complex between NPP and ZrK 1:1 is in equilibrium with monobound and free NPP. Subsequently, hydrolysis of NPP results in P, which is in equilibrium with its monobound form.

Promotion of phosphoester hydrolysis by the ZrIV-based metal-organic framework UiO-67

The ZrIV-based metal-organic framework (MOF) UiO-67 has been examined as a promoter of the hydrolysis of phosphoester bonds by using sodium para-nitrophenylphosphate (pNPP) as a model substrate. The reactions were followed by 1H NMR spectroscopy and performed under mild conditions using 2–100 mol% of the MOF relative to pNPP. All of the systems studied promoted the hydrolysis of pNPP to give para-nitrophenol (pNPh) and inorganic phosphate. A reaction half-life of ca. 30min was achieved using 17 mol% of UiO-67 at 55 °C and 30 mol% at ambient temperature; ≥98% removal of pNPP was reached within 1 h for both reaction temperatures. 1H NMR spectra of the reaction solutions, together with powder X-ray diffraction, FT-IR spectroscopy and solid-state NMR data for the recovered MOF, revealed that (i) pNPP was encapsulated and then converted to pNPh within the cavities of UiO-67, (ii) both pNPh and inorganic phosphate were retained in the solid promoter, and (iii) the MOF suffered partial structural breakdown into the components Zr6O4(OH)4 and 4,4′-biphenyldicarboxylate, with partial release of the latter into solution. These structural changes eventually compromized the recyclability of the promoter, although the material could be recovered and reused in a second cycle without loss of activity.

Solution Speciation of the Dinuclear ZrIV‐Substituted Keggin Polyoxometalate [{α‐PW11O39Zr(μ‐OH)(H2O)}2]8– and Its Reactivity towards DNA‐Model Phosphodiester Hydrolysis

AbstractThe solution speciation of the ZrIV‐substituted Keggin polyoxometalate (Et2NH2)8[{α‐PW11O39Zr(μ‐OH)(H2O)}2]·7H2O (ZrK 2:2) was fully determined under different pD, temperature, and concentration conditions. Subsequently, phosphodiester bond hydrolysis of the DNA model substrate bis(4‐nitrophenyl) phosphate (BNPP) promoted by ZrK 2:2 was studied in detail. In the presence of ZrK 2:2, phosphoester bond hydrolysis in BNPP proceeded with a rate constant of kobs = (4.75 ± 0.25) × 10–6 s–1 at pD 6.4 and 60 °C, which represented a 320‐fold rate enhancement relative to the spontaneous hydrolysis of BNPP. The pD dependence of kobs exhibits a bell‐shaped profile, with the fastest rate observed at pD 6.4. An activation energy (Ea) of 60.16 kJ mol–1, enthalpy of activation (ΔH#) of 57.44 kJ mol–1, entropy of activation (ΔS#) of –173.16 J mol–1 K–1, and Gibbs activation energy (ΔG#) of 111.12 kJ mol–1 at 37 °C were calculated. The influence of the concentration of ZrK 2:2 on the reaction rate constant was studied in the concentration range 0.5 to 6.0 mM. The results showed that ZrK 2:2 is able to hydrolyze an excess amount of BNPP, thus demonstrating that ZrK 2:2 acts as a catalyst for phospho(di)ester bond hydrolysis. In addition, the influence of ionic strength and the inhibitor diphenyl phosphate on BNPP hydrolysis were examined.

Use of Organomolybdenum Compounds for Promoted Hydrolysis of Phosphoester Bonds in Aqueous Media

The dissolution of [{(η5-Ind)Mo(CO)2(μ-Cl)}2] (Ind = indenyl) in N,N-dimethylformamide (DMF) results in the formation of [(η3-Ind)Mo(CO)2Cl(DMF)2], the aerial oxidation of which leads to [Mo2O2(DMF)4(μ-O)2Cl2]. [{(η5-Ind)Mo(CO)2(μ-Cl)}2] and [Mo2O2(DMF)4(μ-O)2Cl2] are examined as promoters of phosphoester bond hydrolysis of para-nitrophenylphosphate (pNPP) in aqueous solution at 55 °C.

Promotion of phosphoester hydrolysis by MoO2Cl2L (L = bipyridine derivatives, H2O, no ligand), MoO2(CH3)2L (L = bipyridine derivatives) and related inorganic–organic hybrids in aqueous media

The compounds MoO2Cl2L (L = 2,2′-bipyridine (bipy) (1); 4,4′-di-tert-butyl-2,2′-bipyridine (di-tBu-bipy) (2)), [MoO2Cl2(H2O)2]·(diglyme)2 (3), MoO2Cl2 (4), MoO2(CH3)2L (L = bipy (5); di-tBu-bipy (6)), [MoO3(bipy)]n (7), {[MoO3(bipy)][MoO3(H2O)]}n (8), [Mo8O22(OH)4(di-tBu-bipy)4] (9) and MoO3 (10) were tested as phosphoester bond hydrolysis promoters in aqueous media. Sodium para-nitrophenylphosphate (pNPP) was used as a model substrate for the phosphoester bond hydrolysis reaction, which was performed at 55 °C, using D2O as solvent and 100 or 10 mol% of the chosen promoter. The progression of all the reactions was monitored by 1H NMR spectroscopy. All studied systems promote phosphoester bond hydrolysis. The best performance was obtained with MoO2Cl2L compounds (1–4) and with the inorganic–organic hybrid {[MoO3(bipy)][MoO3(H2O)]}n (8). The studied compounds originate either homogeneous or solid/liquid biphasic systems. For the biphasic systems (1, 2, 5–9), the solid phase was recovered at the end of the reaction and characterized by FT-IR spectroscopy.

A comparative study on phosphotransferase activity of acid phosphatases from Raoultella planticola and Enterobacter aerogenes on nucleosides, sugars, and related compounds

Natural and modified nucleoside-5'-monophosphates and their precursors are valuable compounds widely used in biochemical studies. Bacterial nonspecific acid phosphatases (NSAPs) are a group of enzymes involved in the hydrolysis of phosphoester bonds, and some of them exhibit phosphotransferase activity. NSAP containing Enterobacter aerogenes and Raoultella planticola whole cells were evaluated in the phosphorylation of a wide range of nucleosides and nucleoside precursors using pyrophosphate as phosphate donor. To increase the productivity of the process, we developed two genetically modified strains of Escherichia coli which overexpressed NSAPs of E. aerogenes and R. planticola. These new recombinant microorganisms (E. coli BL21 pET22b-phoEa and E. coli BL21 pET22b-phoRp) showed higher activity than the corresponding wild-type strains. Reductions in the reaction times from 21 h to 60 min, from 4 h to 15 min, and from 24 h to 40 min in cases of dihydroxyacetone, inosine, and fludarabine, respectively, were obtained.

Use of MoO2Cl2(DMF)2 as a precursor for molybdate promoted hydrolysis of phosphoester bonds

Phosphoester bond cleavage of para-nitrophenylphosphate (pNPP), a commonly used model substrate, is accelerated by using the complex MoO(2)Cl(2)(DMF)(2) (1) (DMF = dimethylformamide) as a hydrolysis promoting agent, even when catalytic amounts of 1 (10 mol% relative to pNPP) are used. The reactions were performed under mild conditions (37-75 °C) and followed by (1)H NMR spectroscopy. For assays performed with high amounts of 1 (1000 mol% relative to pNPP), a white solid (2) precipitates during the initial stages of the reaction, which subsequently dissolves, leading eventually to the precipitation of a less soluble yellow solid (3). Taken together, the characterization data for 2 (FT-IR spectroscopy, elemental analysis, (1)H and (13)C NMR, and electrospray ionization mass spectrometry) indicate that it is a polymeric material with the formula Mo(2)O(6)(DMF)(n) and a structure comprising infinite isopolyoxomolybdate chains built up from edge-shared {MoO(6)} octahedra. Compound 3 was identified as the Keggin-type phosphomolybdate [(CH(3))(2)NH(2)](3)PMo(12)O(40). The formation of 3 is explained by the reaction of inorganic phosphate ions with isopolymolybdate species derived from 2, with dimethylammonium ions arising from the degradation of DMF. Both 2 and 3 are active for phosphoester bond hydrolysis with conversion profiles comparable to the ones obtained with the precursor 1.

Hydrolysis of DNA model substrates catalyzed by metal-substituted Wells–Dawson polyoxometalates

In this study we report the first example of phosphoester bond hydrolysis in 4-nitrophenyl phosphate (NPP) and bis-4-nitrophenyl phosphate (BNPP), two commonly used DNA model substrates, promoted by metal-substituted polyoxometalates (POMs). Different transition metal and lanthanide ions were incorporated into the Wells-Dawson polyoxometalate framework and subsequently screened for their hydrolytic activity towards the cleavage of the phosphoester bonds in NPP and BNPP. From these complexes, the Zr(iv)-substituted POM showed the highest reactivity. At pD 7.2 and 50 °C a NPP hydrolysis rate constant of 7.71 × 10(-4) min(-1) (t(1/2) = 15 h) was calculated, representing a rate enhancement of nearly two orders of magnitude in comparison with the spontaneous hydrolysis of NPP. The catalytic (k(c) = 1.73 × 10(-3) min(-1)) and formation constant (K(f) = 520.02 M(-1)) for the NPP-Zr(iv)-POM complex were determined from kinetic experiments. The reaction proceeded faster in acidic conditions and (31)P NMR experiments showed that faster hydrolysis is proportional to the presence of the 1 : 1 monosubstituted Zr(iv)-POM at acidic pD values. The strong interaction of the 1 : 1 monosubstituted Zr(iv)-POM with the P-O bond of NPP was evidenced by the large chemical shift and the line broadening of the (31)P nucleus in NPP observed upon addition of the metal complex. Significantly, a ten-fold excess of NPP was fully hydrolyzed in the presence of the Zr(iv)-POM, proving the principles of catalysis. The NMR spectra did not show sign of any paramagnetic species, excluding an oxidative cleavage mechanism and suggesting purely hydrolytic cleavage.

Polyoxomolybdate Promoted Hydrolysis of a DNA-Model Phosphoester Studied by NMR and EXAFS Spectroscopy

Hydrolysis of (p-nitrophenyl)phosphate (NPP), a commonly used phosphatase model substrate, was examined in molybdate solutions by means of (1)H, (31)P, and (95)Mo NMR spectroscopy and Mo K-edge Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. At 50 °C and pD 5.1 the cleavage of the phosphoester bond in NPP proceeds with a rate constant of 2.73 × 10(-5) s(-1) representing an acceleration of nearly 3 orders of magnitude as compared to the hydrolysis measured in the absence of molybdate. The pD dependence of k(obs) exhibits a bell-shaped profile, with the fastest cleavage observed in solutions where [Mo(7)O(24)](6-) is the major species in solution. Mixing of NPP and [Mo(7)O(24)](6-) resulted in formation of these two intermediate complexes that were detected by (31)P NMR spectroscopy. Complex A was characterized by a (31)P NMR resonance at -4.27 ppm and complex B was characterized by a (31)P NMR resonance at -7.42 ppm. On the basis of the previous results from diffusion ordered NMR spectroscopy, performed with the hydrolytically inactive substrate phenylphosphonate (PhP), the structure of these two complexes was deduced to be (NPP)(2)Mo(5)O(21)(4-) (complex A) and (NPP)(2)Mo(12)O(36)(H(2)O)(6)(4-) (complex B). The pH studies point out that both complexes are hydrolytically active and lead to the hydrolysis of phosphoester bond in NPP. The NMR spectra did not show evidence of any paramagnetic species, excluding the possibility of Mo(VI) reduction to Mo(V), and indicating that the cleavage of the phosphomonoester bond is purely hydrolytic. The Mo K-edge XANES region also did not show any sign of Mo(VI) to Mo(V) reduction during the hydrolytic reaction. (95)Mo NMR and Mo K-edge EXAFS spectra measured during different stages of the hydrolytic reaction showed a gradual disappearance of [Mo(7)O(24)](6-) during the hydrolytic reaction and appearance of [P(2)Mo(5)O(23)](6-), which was the final complex observed at the end of hydrolytic reaction.

RNA Folding and Hydrolysis Terms Explain ATP Independence of RNA Interference in Human Systems

Although RNA interference (RNAi) has emerged as an important tool for studying the effects of gene knockdown, it is still difficult to predict the success of RNAi effectors in human systems. By examining the basic thermodynamic equations for RNA interactions in RNAi, we demonstrate how the free energies of RNA folding and phosphoester bond hydrolysis can drive RNAi without ATP. Our calculations of RNAi efficiency are close to actual values obtained from in vitro experimental data from 2 previous studies, for both silencing complex formation (2.50 vs. 2.40 for relative efficiency of RISC formation) and mRNA cleavage (0.50 vs. 0.56 for proportion cleaved). Our calculations are also in agreement with previous observations that duplex unwinding and target site folding are major energy barriers to RNAi.

The trigonal-bipyramidal NO4 ligand set in biologically relevant vanadium compounds and their inorganic models

In the present focused review, vanadate-dependent haloperoxidases and vanadate-inhibited enzymes which catalyze the hydrolysis of phosphoester bonds are addressed. In these systems, vanadate [HxVO4](3-x)(-) is covalently coordinated to the imidazolyl moiety of an active site histidine, with a geometrical arrangement close to a trigonal bipyramid. The resulting ligand set, NO4, and ligand arrangement provide peroxidase activity to the haloperoxidases and, to a certain extent, also to vanadate-inhibited phosphatases. The haloperoxidases are responsible for the oxidative halogenation of a variety of organic substrates. They are also active in other oxidation reactions relying on peroxide as the oxidant, such as the oxidative cyclizations of terpenes and, specifically, the oxygenation of (prochiral) sulfides to (chiral) sulfoxides. These functions can be modeled by vanadium complexes. Attracted interest is paid to {V(NO4)} complexes that are functional and structural models of the peroxidases. In the vanadate-inhibited phosphatases - structural analogs of the transition state in phosphoester hydrolysis by the native enzymes - the position of the axial histidine can also be taken by cysteinate or serinate, a fact which has implications for the insulin-mimetic potential of vanadate.

Hydrolysis of Phosphoester Bond by the Heme-Independent Chloroperoxidase from Serratia marcescens

Heme- and metal-independent chloroperoxidase from Serratia marcescens W 250 is shown to be capable of catalyzing the p-nitrophenyl phosphate hydrolysis. The parameters of the phosphatase reaction are determined and inhibitors and activators of the process are found. A hypothetical mechanism of the hydrolysis of phosphoesters by heme- and metal-independent haloperoxidases is suggested.