A Glutathione Peroxidase Mimic 6,6′-Ditellurobis (6-Deoxy-β-Cyclodextrin) with High Substrate Specificity

Glutathione peroxidase (GPx) is one of the most important antioxidative selenoenzymes in living organisms. The novel GPx mimic 6,6′-ditellurobis(6-deoxy-β-cyclodextrin) (6-TeCD) was prepared and evaluated for its capacity to catalyze the reduction of H₂O₂, tert-butyl hydroperoxide (t-BuOOH), and cumene hydroperoxide (CuOOH) by glutathione (GSH) or 3-carboxy-4-nitrobenzenethiol (ArSH). Compared the ArSH assay with the coupled reductase assay, we found that 6-TeCD exhibited strong substrate specificity for aromatic thiol substrate. The specificity led to efficient peroxidase activity almost 100,000-fold than that for a well-known GPx mimic diphenyl diselenide (PhSeSePh). Furthermore, reduction of lipophilic CuOOH was proceeded ca. 30 times faster than the more hydrophilic H₂O₂, which cannot bind into the hydrophobic cavity of β-cyclodextrin. Thus, it seemed that catalytic activity of cyclodextrin-derived GPx models strongly depends on the structurally different both substrates hydroperoxides (ROOH) and thiols.     

Aryl thiol substrate 3-carboxy-4-nitrobenzenethiol strongly stimulating thiol peroxidase activity of glutathione peroxidase mimic 2, 2'-ditellurobis(2-deoxy-beta-cyclodextrin)

Artificial glutathione peroxidase (GPx) model 2, 2'-ditellurobis(2-deoxy-beta-cyclodextrin) (2-TeCD) which has the desirable properties exhibited high substrate specificity and remarkably catalytic efficiency when 3-carboxy-4-nitrobenzenethiol (ArSH) was used as a preferential thiol substrate. The complexation of ArSH with beta-cyclodextrin was investigated through UV spectral titrations, fluorescence spectroscopy, 1H NMR and molecular simulation, and these results indicated that ArSH fits well to the size of the cavity of beta-cyclodextrin. Furthermore, 2-TeCD was found to catalyze the reduction of cumene peroxide (CuOOH) by ArSH 200,000-fold more efficiently than diphenyl diselenide (PhSeSePh). Its steady-state kinetics was studied and the second rate constant kmax/KArSH was found to be 1.05 x 10(7) M(-1) min(-1) and similar to that of natural GPx. Moreover, the kinetic data revealed that the catalytic efficiency of 2-TeCD depended strongly upon the competitive recognition of both substrates for 2-TeCD. The catalytic mechanism of 2-TeCD catalysis agreed well with a ping-pong mechanism, in analogy with natural GPx, and might exert its thiol peroxidase activity via tellurol, tellurenic acid, and tellurosulfide.     

Evaluating substrate specificity of glutathione peroxidase mimic by molecular dynamics simulations and kinetics

The substrate specificities of glutathione peroxidase (GPX) mimic, 6,6′-ditellurobis(6-deoxy-β-cyclodextrin) (6-TeCD), for three hydroperoxides (ROOH), H₂O₂, tert-butyl hydroperoxide (t-BuOOH) and cumene hydroperoxide (CuOOH), are investigated through molecular dynamics (MD) simulations. The most stable conformations and the total interaction energies of complex of 6-TeCD with ROOH are used to evaluate the substrate specificity of 6-TeCD. The steady-state kinetics of 6-TeCD is studied and the Michaelis-Menten constant (K _m) and second-order rate constant k _max/K _ROOH show that 6-TeCD displays different affinity and specificity to ROOH. These results of experiments are well consistent with ones obtained by MD simulations, indicating that MD simulations could be applied to evaluation substrate specificity of small-molecule enzyme mimics.     

Selenium-mediated micellar catalyst: an efficient enzyme model for glutathione peroxidase-like catalysis

Mimicking the properties of the selenoenzyme glutathione peroxidase (GPx) has inspired great interest. In this report, a selenium-containing micellar catalyst was successfully constructed by the self-assembly of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) with benzeneseleninic acid (PhSeO2H) through hydrophobic and electrostatic interaction in water. The selenium-containing micellar catalyst demonstrated substrate specificity for both 3-carboxy-4-nitrobenzenethiol (ArSH, 2) and cumene hydroperoxide (CUOOH), and their complexation was confirmed by UV and fluorescence spectra. More importantly, it demonstrated high GPx activity in two assay systems. It is about 126 times more effective than the well-known GPx mimic ebselen in the classical coupled reductase assay system; however, by using hydrophobic substrate ArSH (2) as an alternative of glutathione (GSH, 1), the micellar catalyst exhibited remarkable 500-fold and 94 500-fold rate enhancements compared with that of PhSeO2H and PhSeSePh.     

Organotellurium-bridged cyclodextrin dimers as artificial glutathione peroxidase models

To elucidate the importance of the goodness of fit in complexes between substrates and glutathione peroxidise (GPX) mimics, we examined the decomposition of a variety of structurally distinct hydroperoxides at the expense of glutathione (GSH) catalyzed by 2,2′-ditellurobis(2-deoxy-γ-cyclodextrin) (2-Te-γ-CD), and by the corresponding derivatives of β-cyclodextrin (β-CD) and α-cyclodextrin. The good fit of the cumene group into the γ-CD binding cavity reflected the result of well-defined reaction geometry, leading to the most excellent peroxidase activity with high substrate specificity. Furthermore, the catalytic constant and the combination with the best binding also exhibited the highest regioselectivity in the substrate decomposition. Saturation kinetics were observed and the catalytic reaction agreed with a ping-pong mechanism, in analogy with natural GPX, and might exert its thiol peroxidase activity via tellurol, tellurenic acid, and tellurosulfide. The stoichiometry of the inclusion complex was determined to be of 2:1 host-to-guest. The value of stability constant K _c for (2-Te-γ-CD)₂/GSH at room temperature was calculated to be 3.815?×?10⁴?M^?2, which suggested that 2-Te-γ-CD had a moderate ability to bind GSH. Importantly, the proposed mode of the (2-TeCD)₂/GSH complex was the possible important noncovalent interactions between enzymes and substrates in influencing catalysis and binding.     

Synthesis, characterization, and antioxidant activity of some ebselen analogues

Simple synthetic routes for several analogues of the anti-inflammatory organoselenium drug, ebselen, are described. The compounds are characterized by (1)H, (13)C, and (77)Se NMR spectroscopy and mass spectral techniques and, in some cases, by single-crystal X-ray diffraction studies. The glutathione peroxidase (GPx)-like antioxidant activity has been studied by using H(2)O(2), tBuOOH, and Cum-OOH as substrates, and thiophenol (PhSH, 4-Me-C(6)H(4)SH) and glutathione (GSH) as cosubstrates. Density functional theory (DFT) calculations have been performed on these systems to understand the effects of various substituents on the (77)Se NMR chemical shifts; these results have been compared with the experimental data. The experimental and theoretical results suggest that the presence of a phenyl substituent on the nitrogen atom is important for the antioxidant activity of ebselen. While ebselen and its analogues are poor catalysts in aromatic thiol assays, these compounds exhibit high GPx activity when GSH is used as the cosubstrate. The poor catalytic activity of ebselen analogues in the presence of aromatic thiols such as PhSH and 4-Me-C(6)H(4)SH can be ascribed to the undesired thiol exchange reaction that takes place at the selenium center due to SeO nonbonding interactions. To understand the effects of different peroxides on the catalytic activities, we have determined the initial rates at various concentrations of GSH and peroxides. These data suggest that the nature of peroxide has little effect on the catalytic efficiencies, although the initial reaction rates observed with hydrogen peroxide were found to be higher than that with tBuOOH and Cum-OOH. In contrast to the effect of peroxides, the nature of thiols appears to have a dramatic effect on the catalytic activity of ebselen and its related derivatives.     

Thiol cofactors for selenoenzymes and their synthetic mimics

The importance of selenium as an essential trace element is now well recognized. In proteins, the redox-active selenium moiety is incorporated as selenocysteine (Sec), the 21st amino acid. In mammals, selenium exerts its redox activities through several selenocysteine-containing enzymes, which include glutathione peroxidase (GPx), iodothyronine deiodinase (ID), and thioredoxin reductase (TrxR). Although these enzymes have Sec in their active sites, they catalyze completely different reactions and their substrate specificity and cofactor or co-substrate systems are significantly different. The antioxidant enzyme GPx uses the tripeptide glutathione (GSH) for the catalytic reduction of hydrogen peroxide and organic peroxides, whereas the larger and more advanced mammalian TrxRs have cysteine moieties in different subunits and prefer to utilize these internal cysteines as thiol cofactors for their catalytic activity. On the other hand, the nature of in vivo cofactor for the deiodinating enzyme ID is not known, although the use of thiols as reducing agents has been well-documented. Recent studies suggest that molecular recognition and effective binding of the thiol cofactors at the active site of the selenoenzymes and their mimics play crucial roles in the catalytic activity. The aim of this perspective is to present an overview of the thiol cofactor systems used by different selenoenzymes and their mimics.     

Synthesis and Structure–Activity Correlation Studies of Secondary‐ and Tertiary‐Amine‐Based Glutathione Peroxidase Mimics

In this study, a series of secondary‐ and tertiary‐amino‐substituted diaryl diselenides were synthesized and studied for their glutathione peroxidase (GPx) like antioxidant activities with H₂O₂, cumene hydroperoxide, or tBuOOH as substrates and with PhSH or glutathione (GSH) as thiol cosubstrates. This study reveals that replacement of the tert‐amino groups in benzylamine‐based diselenides by sec‐amino moieties drastically enhances the catalytic activities in both the aromatic thiol (PhSH) and GSH assay systems. Particularly, the N‐propyl‐ and N‐isopropylamino‐substituted diselenides are 8–18 times more active than the corresponding N,N‐dipropyl‐ and N,N‐diisopropylamine‐based compounds in all three peroxide systems when GSH is used as the thiol cosubstrate. Although the catalytic mechanism of sec‐amino‐substituted diselenides is similar to that of the tert‐amine‐based compounds, differences in the stability and reactivity of some of the key intermediates account for the differences in the GPx‐like activities. It is observed that the sec‐amino groups are better than the tert‐amino moieties for generating the catalytically active selenols. This is due to the absence of any significant thiol‐exchange reactions in the selenenyl sulfides derived from sec‐amine‐based diselenides. Furthermore, the seleninic acids (RSeO₂H) derived from the sec‐amine‐based compounds are more stable toward further reactions with peroxides than their tert‐amine‐based analogues.     

Cyclodextrin-derived chalcogenides as glutathione peroxidase mimics and their protection of mitochondria against oxidative damage

A series of novel glutathione peroxidase (GPx) mimics based on organochalcogen cyclodextrin (CD) dimer were synthesized. Their GPx-like antioxidant activities were studied using hydrogen peroxide H₂O₂, tert-butylhydroperoxide (BHP), and cumene hydroperoxide (CHP) as substrates and glutathione as thiol co-substrate. The results showed that 6A,6B-ditelluronic acid-A,6B′-tellurium bridged γ-cyclodextrin (6-diTe-γ-CD) had the highest peroxidase activity, which was ~670-fold higher than ebselen, a well-known GPx mimic. Reduction of lipophilic CHP often proceeded much faster than reduction of the more hydrophilic H₂O₂ or BHP, which cannot bind into the hydrophobic interior of the CD. The biological activities were also evaluated for their capacity to protect mitochondria against ferrous sulfate/ascorbate-induced oxidative damage. 6-diTe-γ-CD was the best inhibitor which significantly suppressed ferrous sulfate/ascorbate-induced cytotoxicity as determined by swelling of mitochondria, lipid peroxidation and cytochrome c oxidase activity. Our data suggests that 6-diTe-γ-CD has potential pharmaceutical application in the treatment of ROS-mediated diseases.     

Reduction of diphenyl diselenide and analogs by mammalian thioredoxin reductase is independent of their gluthathione peroxidase-like activity: a possible novel pathway for their antioxidant activity

Since the successful use of the organoselenium drug ebselen in clinical trials for the treatment of neuropathological conditions associated with oxidative stress, there have been concerted efforts geared towards understanding the precise mechanism of action of ebselen and other organoselenium compounds, especially the diorganyl diselenides such as diphenyl diselenide, and its analogs. Although the mechanism of action of ebselen and other organoselenium compounds has been shown to be related to their ability to generally mimic native glutathione peroxidase (GPx), only ebselen however has been shown to serve as a substrate for the mammalian thioredoxin reductase (TrxR), demonstrating another component of its pharmacological mechanisms. In fact, there is a dearth of information on the ability of other organoselenium compounds, especially diphenyl diselenide and its analogs, to serve as substrates for the mammalian enzyme thioredoxin reductase. Interestingly, diphenyl diselenide shares several antioxidant and neuroprotective properties with ebselen. Hence in the present study, we tested the hypothesis that diphenyl diselenide and some of its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxy-diphenyl diselenide, 4.4'-biscarboxydiphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could also be substrates for rat hepatic TrxR. Here we show for the first time that diselenides are good substrates for mammalian TrxR, but not necessarily good mimetics of GPx, and vice versa. For instance, bis-methoxydiphenyl diselenide had no GPx activity, whereas it was a good substrate for reduction by TrxR. Our experimental observations indicate a possible dissociation between the two pathways for peroxide degradation (either via substrate for TrxR or as a mimic of GPx). Consequently, the antioxidant activity of diphenyl diselenide and analogs can be attributed to their capacity to be substrates for mammalian TrxR and we therefore conclude that subtle changes in the aryl moiety of diselenides can be used as tool for dissociation of GPx or TrxR pathways as mechanism triggering their antioxidant activities.     

1H NMR Study on the Inclusion Complex of Glutathione with a Glutathione Peroxidase Mimic, 2,2′-ditelluro-bridged β-cyclodextrins

The complex formation of 2, 2′-ditelluro-bis(β-cyclodextrin) (2-TeCD) with glutathione (GSH) was investigated in D₂O at room temperature by ¹H nuclear magnetic resonance(¹H NMR) technique. The association constant and stoichiometry between GSH and 2-TeCD was determined from the chemical shifts dependence of the H5 proton in GSH on the concentration of 2-TeCD. The stoichiometry of the inclusion complex was determined by the molar method to be of 2:1 host-to-guest. 2-TeCD showed higher affinity toward GSH than β-cyclodextrin (β-CD). This may be attributed the reason that 2-TeCD which possesses dual hydrophobic cavities in a close vicinity enhances GSH binding ability through the cooperative binding of two cavities. The formation of the (2-TeCD)₂/GSH complex was one of the reason that 2-TeCD showed higher glutathione peroxidase (GPX) activity than Ebselen.     

Tellurium‐Based Polymeric Surfactants as a Novel Seleno‐Enzyme Model with High Activity

Summary: A tellurium‐based polymeric sufactant as a seleno‐enzyme model has been constructed by employing 11‐acryloyloxyundecyltriethylammonium bromide (AUTEAB, 4 ) and a tellurium‐containing compound ( 1 ). It demonstrates strong substrate binding ability for thiols and high glutathione peroxidase (GPx) activity about 6 orders of magnitude more efficient than the well‐known GPx mimic PhSeSePh in an ArSH assay system. More importantly, a series of tellurium‐based polymeric micelle catalysts with the catalytic tellurium center located at various positions in the micelle have been constructed, and the dramatic difference in activity indicates that the exact match of the catalytic center and binding site plays a key role in enzyme catalytic efficiency.

Schematic representation of the proposed mode of the telluro‐micelle catalysts.     

Catalytic Reduction of Graphene Oxide Nanosheets by Glutathione Peroxidase Mimetics Reveals a New Structural Motif in Graphene Oxide

A catalytic reduction of graphene oxide (GO) by glutathione peroxidase (GPx) mimics is reported. This study reveals that GO contains peroxide functionalities, in addition to the epoxy, hydroxyl and carboxylic acid groups that have been identified earlier. It also is shown that GO acts as a peroxide substrate in the GPx‐like catalytic activity of organoselenium/tellurium compounds. The reaction of tellurol, generated from the corresponding ditelluride, reduces GO through the glutathione (GSH)‐mediated cleavage of the peroxide linkage. The mechanism of GO reduction by the tellurol in the presence of GSH involves the formation of a tellurenic acid and tellurenyl sulfide intermediates. Interestingly, the GPx mimics also catalyze the decarboxylation of the carboxylic acid functionality in GO at ambient conditions. Whereas the selenium/tellurium‐mediated catalytic reduction/decarboxylation of GO may find applications in bioremediation processes, this study suggests that the modification of GO by biologically relevant compounds such as redox proteins must be taken into account when using GO for biomedical applications because such modifications can alter the fundamental properties of GO.     

Imprinted Human Serum Albumin with Antioxidant Activity

In order to create a new mimic of glutathione peroxidase(GPx), bioimprinting was used to generate gluta-thione(GSH) binding site and chemical modification was used to incorporate catalytic group selenocystine(Sec). Human serum albumin(HSA) and S-substituted dinitrophenyl glutathione(GSH-S-DNP) were chosen as the imprinted matrix and imprinting template, respectively, to generate a GSH-imprinted protein(GSH-HSA) by bioimprinting. Sec was incorporated into the GSH-HSA by chemical modification to give a new GP...     

Glutathione peroxidase-like antioxidant activity of diaryl diselenides: a mechanistic study.

The synthesis, structure, and thiol peroxidase-like antioxidant activities of several diaryl diselenides having intramolecularly coordinating amino groups are described. The diselenides derived from enantiomerically pure R-(+)- and S-(-)-N,N-dimethyl(1-ferrocenylethyl)amine show excellent peroxidase activity. To investigate the mechanistic role of various organoselenium intermediates, a detailed in situ characterization of the intermediates has been carried out by (77)Se NMR spectroscopy. While most of the diselenides exert their peroxidase activity via selenol, selenenic acid, and selenenyl sulfide intermediates, the differences in the relative activities of the diselenides are due to the varying degree of intramolecular Se.N interaction. The diselenides having strong Se.N interactions are found to be inactive due to the ability of their selenenyl sulfide derivatives to enhance the reverse GPx cycle (RSeSR + H(2)O(2) = RSeOH). In these cases, the nucleophilic attack of thiol takes place preferentially at selenium rather than sulfur and this reduces the formation of selenol by terminating the forward reaction. On the other hand, the diselenides having weak Se.N interactions are found to be more active due to the fast reaction of the selenenyl sulfide derivatives with thiol to produce diphenyl disulfide and the expected selenol (RSeSR + PhSH = PhSSPh + RSeH). The unsubstituted diaryl diselenides are found to be less active due to the slow reactions of these diselenides with thiol and hydrogen peroxide and also due to the instability of the intermediates. The catalytic cycles of 18 and 19 strongly resemble the mechanism by which the natural enzyme, glutathione peroxidase, catalyzes the reduction of hydroperoxides.     

Synthesis and antioxidant activity of peptide-based ebselen analogues

A series of di- and tripeptide-based ebselen analogues has been synthesized. The compounds were characterized by (1)H, (13)C, and (77)Se NMR spectroscopy and mass spectral techniques. The glutathione peroxidase (GPx)-like antioxidant activity has been studied by using H(2)O(2) , tert-butyl hydroperoxide (tBuOOH), and cumene hydroperoxide (Cum-OOH) as substrates, and glutathione (GSH) as a cosubstrate. Although all the peptide-based compounds have a selenazole ring similar to that of ebselen, the GPx activity of these compounds highly depends on the nature of the peptide moiety attached to the nitrogen atom of the selenazole ring. It was observed that the introduction of a phenylalanine (Phe) amino acid residue in the N-terminal reduces the activity in all three peroxide systems. On the other hand, the introduction of aliphatic amino acid residues such as valine (Val) significantly enhances the GPx activity of the ebselen analogues. The difference in the catalytic activity of dipeptide-based ebselen derivatives can be ascribed mainly to the change in the reactivity of these compounds toward GSH and peroxide. Although the presence of the Val-Ala-CO(2) Me moiety facilitates the formation of a catalytically active selenol species, the reaction of ebselen analogues that has a Phe-Ile-CO(2) Me residue with GSH does not generate the corresponding selenol. To understand the antioxidant activity of the peptide-based ebselen analogues in the absence of GSH, these compounds were studied for their ability to inhibit peroxynitrite (PN)-mediated nitration of bovine serum albumin (BSA) and oxidation of dihydrorhodamine 123. In contrast to the GPx activity, the PN-scavenging activity of the Phe-based peptide analogues was found to be comparable to that of the Val-based compounds. However, the introduction of an additional Phe residue to the ebselen analogue that had a Val-Ala dipeptide significantly reduced the potency of the parent compound in PN-mediated nitration.     

Gene Manipulation Based Selenium-containing Peptide Exhibiting Synergism of SOD and GPx

In this paper, we constructed a novel bifunctional superoxide dismutase（SOD）/glutathione peroxi- dase（GPx） mimic, a selenium-, copper-containing 35-mer peptide conjugate（Se-Cu-35P） in which a three-amino acid linker（（31y-Asn-Gly） connects the C-terminus of 17-mer polypeptide SOD mimic with the N-terminus of 15-mer po- lypeptide GPx mimic. The SOD and GPx activities of Se-Cu-35P are two orders of magnitude lower than those of natural SOD and GPx, respectively. It provides a GPx activity 56-fold higher than Ebselen（a well-known GPx mimic）. The glutathione（GSH） binding constant is 5.6× 10^2 L.mol 1. Se-Cu-35P synergistically resists against the inactivation by H202 and protects the mitochondria from oxidative damage in a dose dependent manner. These results highlight the challenge of generating an efficient SOD/GPx synergism mimic. It could facilitate the studies of the cooperation of GPx and SOD and could be a potential therapeutic agent for the treatment of ROS-mediated diseases,     

A simple and efficient strategy to enhance the antioxidant activities of amino-substituted glutathione peroxidase mimics

The glutathione peroxidase (GPx) activities of some diaryl diselenides incorporating tertiary amino groups were studied with H(2)O(2), Cum-OOH, and tBuOOH as substrates and with PhSH as thiol co-substrate. Simple replacement of a hydrogen atom with a methoxy group dramatically enhances the GPx activity. The introduction of methoxy substituents ortho to selenium in N,N-dialkylbenzylamine-based compounds makes the basicity of the amino groups perfect for the catalysis. The presence of 6-OMe groups prevents possible SeN interactions in the selenols, increasing their zwitterionic characters. The methoxy substituents also protect the selenium in the selenenic acid intermediates from overoxidation to seleninic acids or irreversible inactivation to selenonic acid derivatives. The additional substituents also play a crucial role in the selenenyl sulfide intermediates, by preventing thiol exchange reactions-which would normally lead to an inactivation pathway-at the selenium centers. The strengths of SeN interactions in the selenenyl sulfide intermediates are dramatically reduced upon introduction of the methoxy substituents, which not only reduce the thiol exchange reactions at selenium but also enhance the nucleophilic attack of the incoming thiols at sulfur. The facile attack of thiols at sulfur in the selenenyl sulfides also prevents the reactions between the selenenyl sulfides and H(2)O(2) that can regenerate the selenenic acids (reverse-GPx cycle). These studies reveal that the simple 6-OMe groups play multiple roles in each of the catalytically active intermediates by introducing steric and electronic effects that are required for efficient catalysis.     

桥联双β-环糊精对N-[4-(1-芘基)]丁酰-D/L-苯丙氨酸的手性识别及机理研究

利用紫外-可见吸收和荧光发射光谱, 结合非线性最小二乘法拟合曲线以及分子力学(MM2)模拟系统地研究了手性分子N-[4-(1-芘基)]丁酰-D/L-苯丙氨酸(PDP和PLP, 总称PPs)与β-环糊精(β-CD)、 2-位硒桥联双β-CD(2-SeCD)和2-位碲桥联双β-CD(2-TeCD)的包结能力大小及这3个环糊精对PPs手性识别能力的差异和识别机理. 研究结果表明, PPs不能与单疏水空腔的β-CD形成很好的包结复合物, 与具有较长桥联链的2-TeCD结合能力最强. 2-TeCD与PDP和PLP的结合常数分别为2.33×104和6.07×103 L/mol, 对PPs的手性识别比达到KD/KL=3.84, 高于2-SeCD(KD/KL=2.61). 用MM2模拟得出了PPs与这两个双环糊精形成复合物的三维结构: PPs的绝大部分位于双环糊精两个空腔之间, 但是在这两个复合物中, 苯环与芘环所成的二面角不同. 此外, PPs与这两个双环糊精作用时均存在明显的氢键相互作用, 且2-TeCD强于2-SeCD.     

Modification of Cyclodextrins for Use as Artificial Enzymes

The magical powers of enzymes have been attributed to their ability to bind specific substrates and catalyze reactions of the bound substrate. Artificial enzymes synthetically mimic the binding and the catalytic site to produce molecules that are not only smaller in size but also potentially have similar activity to the real enzymes. The main objective of our research is to create artificial redox enzymes by using cyclodextrins as binding sites and attaching flavin derivatives as the catalytic site. We have developed a strategy to attach a catalytic site to cyclodextrin exclusively at the 2-, 3- or the 6-position. The evaluation of the artificial enzyme in which flavin is attached to the 2-position gives a 647-fold acceleration factor. Although this is modest compared to those of real enzymes (which can have acceleration factors of a trillion), the artificial enzymes allow us to understand the elements that contribute to the incredible catalytic power of enzymes.