In Vitro Evaluation of Neutral Aryloximes as Reactivators for Electrophorus eel Acetylcholinesterase Inhibited by Paraoxon.

Casualties caused by organophosphorus pesticides are a burden for health systems in developing and poor countries. Such compounds are potent acetylcholinesterase irreversible inhibitors, and share the toxic profile with nerve agents. Pyridinium oximes are the only clinically available antidotes against poisoning by these substances, but their poor penetration into the blood-brain barrier hampers the efficient enzyme reactivation at the central nervous system. In searching for structural factors that may be explored in future SAR studies, we evaluated neutral aryloximes as reactivators for paraoxon-inhibited Electrophorus eel acetylcholinesterase. Our findings may result into lead compounds, useful for development of more active compounds for emergencies and supportive care.

Rationally designed molecules for resurgence of cyanide mitigated cytochrome c oxidase activity.

Cytochrome c oxidase (CcOX) containing binuclear heme a3-Cu B centre (BNC) mechanises the process of electron transfer in the last phase of cellular respiration. The molecular modelling based structural analysis of CcOX - heme a3-Cu B complex was performed and the disturbance to this complex under cyanide poisoning conditions was investigated. Taking into consideration the results of molecular docking studies, new chemical entities were developed for clipping cyanide from the enzyme and restoring its normal function. It was found that the molecules obtained by combining syringaldehyde, oxindole and chrysin moieties bearing propyl/butyl spacing groups occupy the BNC region and effectively remove cyanide bound to the enzyme. The binding constant of compound 2 with CN- was 2.3 × 105 M-1 and its ED50 for restoring the cyanide bound CcOX activity in 10 min was 16 µM. The compound interacted with CN- over the pH range 5-10. The comparison of the loss of enzymatic activity in the presence of CN- and resumption of enzymatic activity by compound 2 mediated removal of CN- indicated the efficacy of the compound as antidote of cyanide.

Cucurbit[8]uril Reactivation of an Inactivated Caspase-8 Mutant Reveals Differentiated Enzymatic Substrate Processing.

Caspase-8 constructs featuring an N-terminal FGG sequence allow for selective twofold recognition by cucurbit[8]uril, which leads to an increase of the enzymatic activity in a cucurbit[8]uril dose-dependent manner. This supramolecular switching has enabled for the first time the study of the same caspase-8 in its two extreme states; as full monomer and as cucurbit[8]uril induced dimer. A mutated, fully monomeric caspase-8 (D384A), which is enzymatically inactive towards its natural substrate caspase-3, could be fully reactivated upon addition of cucurbit[8]uril. In its monomeric state caspase-8 (D384A) still processes a small synthetic substrate, but not the natural caspase-3 substrate, highlighting the close interplay between protein dimerization and active site rearrangement for substrate selectivity. The ability to switch the caspase-8 activity by a supramolecular system thus provides a flexible approach to studying the activity of a protein at different oligomerization states.

Alcohol Metabolic Inefficiency: Structural Characterization of Polymorphism-Induced ALDH2 Dysfunctionality and Allosteric Site Identification for Design of Potential Wildtype Reactivators.

Liver mitochondrial aldehyde dehydrogenase 2 (ALDH2) enzyme is responsible for the rapid conversion of acetaldehyde to acetic acid. ALDH2 (E487K) polymorphism results in an inactive allele (ALDH2*2) which cause dysfunctional acetaldehyde metabolism. The 3D structure of an enzyme is crucial to its functionality and a disruption in its structural integrity could result in its metabolic inefficiency and dysfunctionality. Allosteric targeting of polymorphs could facilitate the restoration of wildtype functionalities in ALDH2 polymorphs and serve as an advancement in the treatment of associated diseases. Therefore, structural insights into ALDH2*2 polymorph could reveal the varying degree of alterations which occur at its critical domains and accounts for enzymatic dysfunctionality. In this study, we report the structural characterization of ALDH2*2 polymorph and its critical domains using computational tools. Our findings revealed that the polymorph exhibited significant alterations in stability and flexibility at the catalytic and co-enzyme-binding domain. Moreover, there was an increase in the solvent-exposed surface residues and this indicates structural perturbations. Analysis of the interaction network at ALDH2*2 catalytic domain revealed residual displacement and interaction loss when compared to the wildtype thereby providing insight into the catalytic inefficiency of the polymorph. Interestingly, perturbations induced by ALDH2 polymorphism involves the re-orientation of surface residues, which resulted in the formation of surface exposed pockets. These identified pockets could be potential sites for allosteric targeting. The findings from this study will aid the design of novel site-specific small molecule reactivators with the propensity of restoring wildtype activities for treatment of polymorphic ALDH2 related diseases.

Why is Aged Acetylcholinesterase So Difficult to Reactivate?

Organophosphorus agents are potent inhibitors of acetylcholinesterase. Inhibition involves successive chemical events. The first is phosphylation of the active site serine to produce a neutral adduct, which is a close structural analog of the acylation transition state. This adduct is unreactive toward spontaneous hydrolysis, but in many cases can be reactivated by nucleophilic medicinal agents, such as oximes. However, the initial phosphylation reaction may be followed by a dealkylation reaction of the incipient adduct. This reaction is called aging and produces an anionic phosphyl adduct with acetylcholinesterase that is refractory to reactivation. This review considers why the anionic aged adduct is unreactive toward nucleophiles. An alternate approach is to realkylate the aged adduct, which would render the adduct reactivatable with oxime nucleophiles. However, this approach confronts a considerable-and perhaps intractable-challenge: the aged adduct is a close analog of the deacylation transition state. Consequently, the evolutionary mechanisms that have led to transition state stabilization in acetylcholinesterase catalysis are discussed herein, as are the challenges that they present to reactivation of aged acetylcholinesterase.

Molecular architectures and functions of radical enzymes and their (re)activating proteins.

Certain proteins utilize the high reactivity of radicals for catalysing chemically challenging reactions. These proteins contain or form a radical and therefore named 'radical enzymes'. Radicals are introduced by enzymes themselves or by (re)activating proteins called (re)activases. The X-ray structures of radical enzymes and their (re)activases revealed some structural features of these molecular apparatuses which solved common enigmas of radical enzymes­i.e. how the enzymes form or introduce radicals at the active sites, how they use the high reactivity of radicals for catalysis, how they suppress undesired side reactions of highly reactive radicals and how they are (re)activated when inactivated by extinction of radicals. This review highlights molecular architectures of radical B12 enzymes, radical SAM enzymes, tyrosyl radical enzymes, glycyl radical enzymes and their (re)activating proteins that support their functions. For generalization, comparisons of the recently reported structures of radical enzymes with those of canonical radical enzymes are summarized here.

Development of surface modified biodegradable polymeric nanoparticles to deliver GSE24.2 peptide to cells: a promising approach for the treatment of defective telomerase disorders.

The aim of the present study was to develop a novel strategy to deliver intracellularly the peptide GSE24.2 for the treatment of Dyskeratosis congenita (DC) and other defective telomerase disorders. For this purpose, biodegradable polymeric nanoparticles using poly(lactic-co-glycolic acid) (PLGA NPs) or poly(lactic-co-glycolic acid)-poly ethylene glycol (PLGA-PEG NPs) attached to either polycations or cell-penetrating peptides (CPPs) were prepared in order to increase their cellular uptake. The particles exhibited an adequate size and zeta potential, with good peptide loading and a biphasic pattern obtained in the in vitro release assay, showing an initial burst release and a later sustained release. GSE24.2 structural integrity after encapsulation was assessed using SDS-PAGE, revealing an unaltered peptide after the NPs elaboration. According to the cytotoxicity results, cell viability was not affected by uncoated polymeric NPs, but the incorporation of surface modifiers slightly decreased the viability of cells. The intracellular uptake exhibited a remarkable improvement of the internalization, when the NPs were conjugated to the CPPs. Finally, the bioactivity, addressed by measuring DNA damage rescue and telomerase reactivation, showed that some formulations had the lowest cytotoxicity and highest biological activity. These results proved that GSE24.2-loaded NPs could be delivered to cells, and therefore, become an effective approach for the treatment of DC and other defective telomerase syndromes.

Essential roles of nucleotide-switch and metal-coordinating residues for chaperone function of diol dehydratase-reactivase.

Diol dehydratase-reactivase (DD-R) is a molecular chaperone that reactivates inactivated holodiol dehydratase (DD) by cofactor exchange. Its ADP-bound and ATP-bound forms are high-affinity and low-affinity forms for DD, respectively. Among DD-Rs mutated at the nucleotide-binding site, neither the Dα8N nor Dα413N mutant was effective as a reactivase. Although Dα413N showed ATPase activity, it did not mediate cyanocobalamin (CN-Cbl) release from the DD·CN-Cbl complex in the presence of ATP or ADP and formed a tight complex with apoDD even in the presence of ATP, suggesting the involvement of Aspα413 in the nucleotide switch. In contrast, Dα8N showed very low ATPase activity and did not mediate CN-Cbl release from the complex in the presence of ATP, but it did cause about 50% release in the presence of ADP. The complex formation of this mutant with DD was partially reversed by ATP, suggesting that Aspα8 is involved in the ATPase activity but only partially in the nucleotide switch. Among DD-Rs mutated at the Mg(2+)-binding site, only Eß31Q was about 30% as active as wild-type DD-R and formed a tight complex with apoDD, indicating that the DD-R ß subunit is not absolutely required for reactivation. If subunit swapping occurs between the DD-R ß and DD ß subunits, Gluß97 of DD would coordinate to Mg(2+). The complex of Eß97Q DD with CN-Cbl was not activated by wild-type DD-R. No complex was formed between this mutant and wild-type DD-R, indicating that the coordination of Gluß97 to Mg(2+) is essential for subunit swapping and therefore for (re)activation.

Divergent structure-activity relationships of structurally similar acetylcholinesterase inhibitors.

The molecular interactions between the enzyme acetylcholinesterase (AChE) and two compound classes consisting of N-[2-(diethylamino)ethyl]benzenesulfonamides and N-[2-(diethylamino)ethyl]benzenemethanesulfonamides have been investigated using organic synthesis, enzymatic assays, X-ray crystallography, and thermodynamic profiling. The inhibitors' aromatic properties were varied to establish structure-activity relationships (SAR) between the inhibitors and the peripheral anionic site (PAS) of AChE. The two structurally similar compound classes proved to have distinctly divergent SARs in terms of their inhibition capacity of AChE. Eight X-ray structures revealed that the two sets have different conformations in PAS. Furthermore, thermodynamic profiles of the binding between compounds and AChE revealed class-dependent differences of the entropy/enthalpy contributions to the free energy of binding. Further development of the entropy-favored compound class resulted in the synthesis of the most potent inhibitor and an extension beyond the established SARs. The divergent SARs will be utilized to develop reversible inhibitors of AChE into reactivators of nerve agent-inhibited AChE.

Covalent inhibition of recombinant human carboxylesterase 1 and 2 and monoacylglycerol lipase by the carbamates JZL184 and URB597.

Carboxylesterase type 1 (CES1) and CES2 are serine hydrolases located in the liver and small intestine. CES1 and CES2 actively participate in the metabolism of several pharmaceuticals. Recently, carbamate compounds were developed to inhibit members of the serine hydrolase family via covalent modification of the active site serine. URB597 and JZL184 inhibit fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively; however, carboxylesterases in liver have been identified as a major off-target. We report the kinetic rate constants for inhibition of human recombinant CES1 and CES2 by URB597 and JZL184. Bimolecular rate constants (k(inact)/K(i)) for inhibition of CES1 by JZL184 and URB597 were similar [3.9 (±0.2) × 10(3) M(-1) s(-1) and 4.5 (±1.3) × 10(3) M(-1) s(-1), respectively]. However, k(inact)/K(i) for inhibition of CES2 by JZL184 and URB597 were significantly different [2.3 (±1.3) × 10(2) M(-1) s(-1) and 3.9 (±1.0) × 10(3) M(-1) s(-1), respectively]. Rates of inhibition of CES1 and CES2 by URB597 were similar; however, CES1 and MAGL were more potently inhibited by JZL184 than CES2. We also determined kinetic constants for spontaneous reactivation of CES1 carbamoylated by either JZL184 or URB597 and CES1 diethylphosphorylated by paraoxon. The reactivation rate was significantly slower (4.5×) for CES1 inhibited by JZL184 than CES1 inhibited by URB597. Half-life of reactivation for CES1 carbamoylated by JZL184 was 49 ± 15 h, which is faster than carboxylesterase turnover in HepG2 cells. Together, the results define the kinetics of inhibition for a class of drugs that target hydrolytic enzymes involved in drug and lipid metabolism.

Nonquaternary reactivators for organophosphate-inhibited cholinesterases.

A new class of amidine-oxime reactivators of organophosphate (OP)-inhibited cholinesterases (ChE) was synthesized and tested in vitro and in vivo. Compared with 2-PAM, the most promising cyclic amidine-oxime (i.e., 12e) showed comparable or greater reactivation of OP-inactivated AChE and OP-inactivated BChE. To the best of our knowledge, this is the first report of a nonquaternary oxime that has, comparable to 2-PAM, in vitro potency for reactivation of Sarin (GB)-inhibited AChE and BChE. Amidine-oximes were tested in vitro, and reactivation rates for OP-inactivated butyrylcholinesterase (BChE) were greater than those for 2-PAM or MINA. Amidine-oxime reactivation rates for OP-inactivated acetylcholinesterase (AChE) were lower compared to 2-PAM but greater compared with MINA. Amidine-oximes were tested in vivo for protection against the toxicity of nerve agent model compounds. (i.e., a model of Sarin). Post-treatment (i.e., 5 min after OP exposure, i.p,) with amidine oximes 7a-c and 12a, 12c, 12e, 12f, and 15b (145 µmol/kg, i.p.) protected 100% of the mice challenged with the sarin model compound. Even at 25% of the initial dose of amidine-oxime (i.e., a dose of 36 µmol/kg, i.p.), 7b and 12e protected 100% of the animals challenged with the sarin nerve agent model compound that caused lethality in 6/11 animals without amidine-oxime.

Enzyme reactivation by hydrogen peroxide in heme-based tryptophan dioxygenase.

An intriguing mystery about tryptophan 2,3-dioxygenase is its hydrogen peroxide-triggered enzyme reactivation from the resting ferric oxidation state to the catalytically active ferrous form. In this study, we found that such an odd Fe(III) reduction by an oxidant depends on the presence of L-Trp, which ultimately serves as the reductant for the enzyme. In the peroxide reaction with tryptophan 2,3-dioxygenase, a previously unknown catalase-like activity was detected. A ferryl species (δ = 0.055 mm/s and ΔE(Q) = 1.755 mm/s) and a protein-based free radical (g = 2.0028 and 1.72 millitesla linewidth) were characterized by Mössbauer and EPR spectroscopy, respectively. This is the first compound ES-type of ferryl intermediate from a heme-based dioxygenase characterized by EPR and Mössbauer spectroscopy. Density functional theory calculations revealed the contribution of secondary ligand sphere to the spectroscopic properties of the ferryl species. In the presence of L-Trp, the reactivation was demonstrated by enzyme assays and by various spectroscopic techniques. A Trp-Trp dimer and a monooxygenated L-Trp were both observed as the enzyme reactivation by-products by mass spectrometry. Together, these results lead to the unraveling of an over 60-year old mystery of peroxide reactivation mechanism. These results may shed light on how a metalloenzyme maintains its catalytic activity in an oxidizing environment.

Amidine-oximes: reactivators for organophosphate exposure.

A new class of amidine-oxime reactivators of organophosphate (OP)-inhibited cholinesterases (ChE) were designed, synthesized, and tested. These compounds represent a novel group of oximes with enhanced capabilities of crossing the blood-brain barrier. Lack of brain penetration is a major limitation for currently used oximes as antidotes of OP poisoning. The concept described herein relies on a combination of an amidine residue and oxime functionality whereby the amidine increases the binding affinity to the ChE and the oxime is responsible for reactivation. Amidine-oximes were tested in vitro and reactivation rates for OP-BuChE were greater than pralidoxime (2-PAM) or monoisonitrosoacetone (MINA). Amidine-oxime reactivation rates for OP-AChE were lower compared to 2-PAM but greater compared with MINA. After pretreatment for 30 min with oximes 15c and 15d (145 µmol/kg, ip) mice were challenged with a soman model compound. In addition, 15d was tested in a post-treatment experiment (145 µmol/kg, ip, administration 5 min after sarin model compound exposure). In both cases, amidine-oximes afforded 100% 24 h survival in an animal model of OP exposure.

Diol dehydratase-reactivating factor is a reactivase--evidence for multiple turnovers and subunit swapping with diol dehydratase.

Adenosylcobalamin-dependent diol dehydratase (DD) undergoes suicide inactivation by glycerol, one of its physiological substrates, resulting in the irreversible cleavage of the coenzyme Co-C bond. The damaged cofactor remains tightly bound to the active site. The DD-reactivating factor reactivates the inactivated holoenzyme in the presence of ATP and Mg(2+) by mediating the exchange of the tightly bound damaged cofactor for free intact coenzyme. In this study, we demonstrated that this reactivating factor mediates the cobalamin exchange not stoichiometrically but catalytically in the presence of ATP and Mg(2+). Therefore, we concluded that the reactivating factor is a sort of enzyme. It can be designated DD reactivase. The reactivase showed broad specificity for nucleoside triphosphates in the activation of the enzyme·cyanocobalamin complex. This result is consistent with the lack of specific interaction with the adenine ring of ADP in the crystal structure of the reactivase. The specificities of the reactivase for divalent metal ions were also not strict. DD formed 1:1 and 1:2 complexes with the reactivase in the presence of ADP and Mg(2+). Upon complex formation, one ß subunit was released from the (αß)2 tetramer of the reactivase. This result, together with the similarity in amino acid sequences and folds between the DD ß subunit and the reactivase ß subunit, suggests that subunit displacement or swapping takes place upon formation of the enzyme·reactivase complex. This would result in the dissociation of the damaged cofactor from the inactivated holoenzyme, as suggested by the crystal structures of the reactivase and DD.

Thiadiazole carbamates: potent inhibitors of lysosomal acid lipase and potential Niemann-Pick type C disease therapeutics.

Niemann-Pick type C (NPC) disease is a lysosomal storage disorder characterized at the cellular level by abnormal accumulation of cholesterol and other lipids in lysosomal storage organelles. Lysosomal acid lipase (LAL) has been recently identified as a potential therapeutic target for NPC. LAL can be specifically inhibited by a variety of 3,4-disubstituted thiadiazole carbamates. An efficient synthesis of the C(3) oxygenated/C(4) aminated analogues has been developed that furnishes the products in high yields and high degrees of purity. Common intermediates can also be used for the synthesis of the C(3) carbon substituted derivatives. Herein we tested various thiadiazole carbamates, amides, esters, and ketones for inhibition of LAL. In addition, we tested a diverse selection of commercially available non-thiadiazole carbamates. Our studies show that, among the compounds examined herein, only thiadiazole carbamates are effective inhibitors of LAL. We present a mechanism for LAL inhibition by these compounds whereby LAL transiently carbamoylates the enzyme similarly to previously described inhibition of acetylcholinesterase by rivastigmine and other carbamates as well as acylation of various lipases by orlistat.

Four flavonoids from Echinosophora koreensis and their effects on alcohol metabolizing enzymes.

A new prenylated dihydroflavonol, 3-hydroxy-kenusanone B 1, as well as three other known isoflavanones, sophoronol 2, sophoraisoflavanone A 3 and kenusanone H 4, were isolated from the rhizomes of Echinosophora koreensis. The structures of these compounds were elucidated using spectroscopic analyses that included extensive 2D NMR, optical rotation spectrometry and mass spectrometry. All four flavonoids enhanced the activities of alcohol metabolizing enzymes such as alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) at micromolar concentrations. Sophoronol 2 showed a nine-fold increased activation of alcohol dehydrogenase and aldehyde dehydrogenase than a negative control group at concentrations of 100 microg/mL and 50 microg/mL, respectively. This study suggests that prenylated flavonoids have the potential to prevent 'hangovers' after alcohol intake.

Oximes: Reactivators of phosphorylated acetylcholinesterase and antidotes in therapy against tabun poisoning.

One of the therapeutic approaches to organophosphate poisoning is to reactivate AChE with site-directed nucleophiles such as oximes. However, pyridinium oximes 2-PAM, HI-6, TMB-4 and obidoxime, found as the most effective reactivators, have limiting reactivating potency in tabun poisoning. We tested oximes varying in the type of ring (pyridinium and/or imidazolium), the length and type of the linker between rings, and in the position of the oxime group on the ring to find more effective oximes to reactivate tabun-inhibited human erythrocyte AChE. Three of our tested pyridinium oximes K027, K048, K074, along with TMB-4, were the most promising for AChE reactivation. Promising oximes were further tested in vivo on tabun poisoned mice not only as antidotes in combination with atropine but also as pretreatment drug. Herein, we showed that a promising treatment in tabun poisoning by selected oximes and atropine could be improved if oximes are also used in pretreatment. Since the reactivating efficacy of the oximes in vitro corresponded to their therapeutic efficacy in vivo, it seems that pharmacological effect of these oximes is indeed primarily related to the reactivation of tabun-phosphorylated AChE.

Inhibitors of the molybdenum cofactor containing 4-hydroxybenzoyl-CoA reductase.

4-Hydroxybenzoyl-CoA reductase (4-HBCR) is a member of the xanthine oxidase (XO) family of molybdenum cofactor containing enzymes and catalyzes the irreversible removal of a phenolic hydroxy group by reduction, yielding benzoyl-CoA and water. In this work the effects of various activity modulating compounds were characterized by kinetic, electron paramagnetic resonance (EPR) spectroscopic, and X-ray crystallographic studies. 4-HBCR was readily inactivated by cyanide and by the reducing agents titanium(III) citrate and dithionite; in contrast, reduced viologens had no inhibitory effect. Cyanide inhibition occurred in both the oxidized and reduced state of 4-HBCR. In the reduced state, cyanide-inhibited 4-HBCR was reactivated by simple oxidation. In contrast, reactivation from the oxidized state was only achieved in the presence of sulfide. Dithionite-inhibited 4-HBCR was reactivated by oxidation, whereas inhibition by titanium(III) citrate was irreversible. The previously reported inhibitory effect of azide could not be confirmed; instead, azide rather protected the enzyme from inactivation by titanium(III) citrate. The EPR spectra of the Mo(V) states were nearly identical in the noninhibited methyl viologen and in the dithionite-inhibited states of 4-HBCR; they exhibited a hyperfine splitting due to magnetic coupling with two solvent-exchangeable protons. The cyanide-treated enzyme showed the typical desulfo-inhibited Mo(V) EPR signal in D 2O, whereas in H 2O the hyperfine splitting was altered but indicated no loss of Mo(V)-proton interactions. The structures of dithionite- and azide-bound 4-HBCR were solved at 2.1 and 2.2 A, respectively. Both dithionite and azide bound directly to equatorial ligation sites of the Mo atom. The results obtained revealed further insights into the active site of an unusual member of the XO family of molybdenum cofactor containing enzymes.

Molecular basis for specificities of reactivating factors for adenosylcobalamin-dependent diol and glycerol dehydratases.

Adenosylcobalamin-dependent diol and glycerol dehydratases are isofunctional enzymes and undergo mechanism-based inactivation by a physiological substrate glycerol during catalysis. Inactivated holoenzymes are reactivated by their own reactivating factors that mediate the ATP-dependent exchange of an enzyme-bound, damaged cofactor for free adenosylcobalamin through intermediary formation of apoenzyme. The reactivation takes place in two steps: (a) ADP-dependent cobalamin release and (b) ATP-dependent dissociation of the resulting apoenzyme-reactivating factor complexes. The in vitro experiments with purified proteins indicated that diol dehydratase-reactivating factor (DDR) cross-reactivates the inactivated glycerol dehydratase, whereas glycerol dehydratase-reactivating factor (GDR) did not cross-reactivate the inactivated diol dehydratase. We investigated the molecular basis of their specificities in vitro by using purified preparations of cognate and noncognate enzymes and reactivating factors. DDR mediated the exchange of glycerol dehydratase-bound cyanocobalamin for free adeninylpentylcobalamin, whereas GDR cannot mediate the exchange of diol dehydratase-bound cyanocobalamin for free adeninylpentylcobalamin. As judged by denaturing PAGE, the glycerol dehydratase-DDR complex was cross-formed, although the diol dehydratase-GDR complex was not formed. There were no specificities of reactivating factors in the ATP-dependent dissociation of enzyme-reactivating factor complexes. Thus, it is very likely that the specificities of reactivating factors are determined by the capability of reactivating factors to form complexes with apoenzymes. A modeling study based on the crystal structures of enzymes and reactivating factors also suggested why DDR cross-forms a complex with glycerol dehydratase, and why GDR does not cross-form a complex with diol dehydratase.

Oxime-induced reactivation of sarin-inhibited AChE: a theoretical mechanisms study.

Oximes (especially oximate anions) are used as potential reactivators of OP-inhibited AChE due to their unique alpha-effect nucleophilic reactivity. In the present study, by applying the DFT approach at the B3LYP/6-311G(d,p) level and the Møller-Plesset perturbation theory at the MP2/6-311G(d,p) level, the formoximate-induced reactivation patterns of the sarin-AChE adduct and the corresponding reaction mechanism have been investigated. The potential energy surface along the pathway of the reactivation reaction of sarin-inhibited AChE by oxime reveals that the reaction can occur quickly due to the relatively low energy barriers. A two-step process is a major pathway proposed for the studied reactivation reaction. Through the nucleophilic attack, the oximate first binds to the sarin-AChE adduct to form a relatively stable phosphorus complex. The regeneration of the serine takes place subsequently through an elimination step, which is expected to be competitive with the nucleophilic attacking process. The polarizable continuum model (PCM) has been applied to evaluate the solvate effects on the pathway. It is concluded that the reaction energy barriers are also low enough for the reaction to easily occur in solvent. The results derived from both the gas-phase model and the aqueous solvation model suggest that the studied oximate anion is an efficient antidote reagent for sarin-inhibited AChE.