Kaplan D

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Full name : Kaplan Dana

First name : Dana

Mail : Department of Organic Chemistry, Israel Institute for Biological Research, P.O. Box 19, Ness-Ziona 74100

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Country : Israel

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References (17)

Title : Decomposition of adsorbed VX on activated carbons studied by 31P MAS NMR - Columbus_2006_Environ.Sci.Technol_40_3952
Author(s) : Columbus I , Waysbort D , Shmueli L , Nir I , Kaplan D
Ref : Environ Sci Technol , 40 :3952 , 2006
Abstract : The fate of the persistent OP nerve agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) on granular activated carbons that are used for gas filtration was studied by means of 31P magic angle spinning (MAS) NMR spectroscopy. VX as vapor or liquid was adsorbed on carbon granules, and MAS NMR spectra were recorded periodically. The results show that at least 90% of the adsorbed VX decomposes within 20 days or less to the nontoxic ethyl methylphosphonic acid (EMPA) and bis(S-2-diisopropylaminoethane) {(DES)2}. Decomposition occurred irrespective of the phase from which VX was loaded, the presence of metal impregnation on the carbon surface, and the water content of the carbon. Theoretical and practical aspects of the degradation are discussed.
ESTHER : Columbus_2006_Environ.Sci.Technol_40_3952
PubMedSearch : Columbus_2006_Environ.Sci.Technol_40_3952
PubMedID: 16830567

Title : The role of AChE active site gorge in determining stereoselectivity of charged and noncharged VX enantiomers - Ordentlich_2005_Chem.Biol.Interact_157-158_191
Author(s) : Ordentlich A , Barak D , Sod-Moriah G , Kaplan D , Mizrahi D , Segall Y , Kronman C , Karton Y , Lazar A , Marcus D , Velan B , Shafferman A
Ref : Chemico-Biological Interactions , 157-158 :191 , 2005
Abstract : The reactivity of human acetylcholinesterase (HuAChE) toward the chemical warfare agent VX [O-ethyl S-[2-(diisopropylamino)ethyl] methyl-phosphonothioate] and its stereoselectivity toward the P(S)-enantiomer were investigated by examining the reactivity of HuAChE and its mutant derivatives toward purified enantiomers of VX and its noncharged isostere nc-VX [O-ethyl S-(3-isopropyl-4-methyl-pentyl) methylphosphonothioate]. Stereoselectivity of the wild-type HuAChE toward VX(S) is manifested by a 115-fold higher bimolecular rate constant (1.4 x 10(8) min(-1) M(-1)) as compared to that of VX(R). HuAChE was also 12,500-fold more reactive toward VX(S) than toward nc-VX(S), demonstrating the significance of the polar interactions of the ammonium substituent to their overall affinity toward VX. Indeed, substitution of the cation-binding subsite residue Trp86 by alanine resulted in a decrease of three orders of magnitude in HuAChE reactivity toward both VX enantiomers, with only a marginal effect on the reactivity toward the enantiomers of nc-VX. These results demonstrate that accommodation of the charged moieties of both VX enantiomers depends predominantly on interactions with the aromatic moiety of Trp86. Yet, these interactions seem to limit the stereoselectivity toward the P(S)-enantiomer, which for charged methylphosphonates is much lower than for the noncharged analogs, like sarin or soman. Marked decrease in stereoselectivity toward VX(S) was observed following replacements of Phe295 at the acyl pocket (F295A and F295A/F297A). Replacement of the peripheral anionic site (PAS) residue Asp74 by asparagine (D74N) practically abolished stereoselectivity toward VX(S) (a 130-fold decrease), while substitution which retained the negative charge at position 74 (D74E) had no effect. The results from kinetic studies and molecular simulations suggest that the differential reactivity toward the VX enantiomers originates predominantly from a different orientation of the charged leaving group with respect to residue Asp74. Such different orientations of the charged leaving group in the HuAChE adducts of the VX enantiomers seem to be a consequence of intramolecular interactions with the bulky phosphorus alkoxy group.
ESTHER : Ordentlich_2005_Chem.Biol.Interact_157-158_191
PubMedSearch : Ordentlich_2005_Chem.Biol.Interact_157-158_191
PubMedID: 16289014

Title : Functional requirements for the optimal catalytic configuration of the AChE active center - Shafferman_2005_Chem.Biol.Interact_157-158_123
Author(s) : Shafferman A , Barak D , Kaplan D , Ordentlich A , Kronman C , Velan B
Ref : Chemico-Biological Interactions , 157-158 :123 , 2005
Abstract : Functional analysis of the HuAChE active center architecture revealed that accommodation of structurally diverse substrates and other ligands is achieved through interactions with specific subsites such as the acyl pocket, cation binding site, hydrophobic site or the oxyanion hole. Recent studies have begun to unravel the role of this active center architecture in maintaining the optimal catalytic facility of the enzyme through inducing proper alignment of the catalytic triad. The exact positioning of the catalytic glutamate (Glu334) seems to be determined by a hydrogen bond network including several polar residues and water molecules. Disruption of this network by replacement of Ser229 by alanine is thought to remove the Glu334 carboxylate from the vicinity of His447 abolishing catalytic activity. The proper orientation of the catalytic histidine side chain is maintained by these polar interactions as well as through "aromatic trapping" by residues lining the HuAChE active center gorge. Thus, replacement of aromatic residues in the vicinity of His447, as in the F295A/F338A or in the Y72N/Y124Q/W286A/F295L/F297V/Y337A (hexamutant which mimicks the aromatic lining of HuBChE) enzymes, resulted in a dramatic decrease in catalytic activity, which was proposed to originate from catalytically nonproductive mobility of His447. Yet, HuBChE is catalytically efficient indicating that "aromatic trapping" is not the only way to conformationally stabilize the His447 side chain. A possible restriction of this mobility in a series of F295X/F338A HuAChEs was examined in silico followed by site-directed mutagenesis. Both simulations and reactivities of the actual F295X/F338A enzymes, carrying various aliphatic residues at position 295, indicate that of the bulky amino acids, like leucine or isoleucine, only methionine was capable of maintaining the catalytically viable conformation of His447. The F295M/F338A HuAChE was only two-fold less reactive than the F338A enzyme toward acetylthiocholine, and exhibited wild type-like reactivity toward covalent modifiers of the catalytic Ser203. The findings are consistent with the notion that different combinations of steric interference and specific polar interactions serve to maintain the position of His447 and thereby the high efficiency of the catalytic machinery. The two seemingly conflicting demands on the architecture of the active center-flexible accommodation of substrate and optimal juxtaposition of residues of the catalytic triad, demonstrate the truly amazing molecular design of the AChE active center.
ESTHER : Shafferman_2005_Chem.Biol.Interact_157-158_123
PubMedSearch : Shafferman_2005_Chem.Biol.Interact_157-158_123
PubMedID: 16256968

Title : Lessons from functional analysis of AChE covalent and noncovalent inhibitors for design of AD therapeutic agents - Barak_2005_Chem.Biol.Interact_157-158_219
Author(s) : Barak D , Ordentlich A , Kaplan D , Kronman C , Velan B , Shafferman A
Ref : Chemico-Biological Interactions , 157-158 :219 , 2005
Abstract : Determination of the 3D-structure of acetylcholinesterase (AChE) of Torpedo californica over a decade ago, and more recently that of human enzyme together with extensive targeted mutagenesis of the mammalian AChEs led to a fine mapping of the multiple functional domains within the active center of the enzyme. Many of the contributions of this active center architecture to accommodation of noncovalent ligands could be deduced from the X-ray structures of the corresponding HuAChE complexes. Yet, Michaelis complexes leading to transient covalent adducts are not amenable to structural analysis. Since the rates of formation of the covalent adducts depend predominantly on the stabilities of the corresponding Michaelis complexes, it is essential to characterize the specific interactions contributing to stabilization of these complexes. Functional analysis of interactions with HuAChE enzymes allows for such characterization for carbamates, like pyridostigmine or rivastigmine, much in the same way as that for the noncovalent therapeutic ligands nivalin or aricept. In fact, the observed differences between the affinities toward carbamates and the noncovalent ligands seem to result from specific structural characteristics of the inhibitors rather than from the decomposition path of the particular complex. Replacements at the cation binding site (Trp86), hydrogen bond network (Glu202, Tyr133, Glu450), and hydrophobic pocket result in similar effects for the covalent as well as for the noncovalent inhibitors. Also, while the effects of perturbing the aromatic trapping of the catalytic His447 for pyridostigmine and nivalin were analogous to those for the substrate, the corresponding effects for rivastigmine and aricept were quite different. Thus, elucidation of the functional architecture of the HuAChE active center is bound to be of considerable utility in the current effort to design novel covalent AChE inhibitors as therapeutics for Alzheimer's disease (AD).
ESTHER : Barak_2005_Chem.Biol.Interact_157-158_219
PubMedSearch : Barak_2005_Chem.Biol.Interact_157-158_219
PubMedID: 16289124

Title : Surprising findings from the functional analysis of human acetylcholinesterase adducts of Alzheimer?s disease drugs. -
Author(s) : Ordentlich A , Barak D , Ariel N , Kronman C , Kaplan D , Velan B , Shafferman A
Ref : Cholinergic Mechanisms, CRC Press :177 , 2004
PubMedID:

Title : Attempts to engineer an enzyme mimic of butyrylcholinesterase by substitution of the six divergent aromatic amino acids in the active center of acetylcholinesterase. -
Author(s) : Kaplan D , Ordentlich A , Barak D , Ariel N , Kronman C , Baruch V , Shafferman A
Ref : Cholinergic Mechanisms, CRC Press :601 , 2004
PubMedID:

Title : MALDI-TOF\/MS analysis of tabun-acetylcholinesterase conjugate. -
Author(s) : Elhanany E , Ordentlich A , Dgany OR , Kaplan D , Segall Y , Barak R , Velan B , Shafferman A
Ref : Cholinergic Mechanisms, CRC Press :563 , 2004
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Title : Poster (14) The aromatic trapping of histidine 447 in catalysis of acetylcholinesterases -
Author(s) : Shafferman A , Barak D , Kaplan D , Ordentlich A , Ariel N , Velan B
Ref : In: Cholinesterases in the Second Millennium: Biomolecular and Pathological Aspects , (Inestrosa NC, Campos EO) P. Universidad Catolica de Chile-FONDAP Biomedicina :327 , 2004
PubMedID:

Title : The aromatic trapping of histidine 447 in catalysis of acetylcholinesterases -
Author(s) : Shafferman A , Barak D , Kaplan D , Ordentlich A , Ariel N , Velan B
Ref : In: Cholinesterases in the Second Millennium: Biomolecular and Pathological Aspects , (Inestrosa NC, Campos EO) P. Universidad Catolica de Chile-FONDAP Biomedicina :181 , 2004
PubMedID:

Title : Stereoselectivity toward VX is determined by interactions with residues of the acyl pocket as well as of the peripheral anionic site of AChE - Ordentlich_2004_Biochemistry_43_11255
Author(s) : Ordentlich A , Barak D , Sod-Moriah G , Kaplan D , Mizrahi D , Segall Y , Kronman C , Karton Y , Lazar A , Marcus D , Velan B , Shafferman A
Ref : Biochemistry , 43 :11255 , 2004
Abstract : The origins of human acetylcholinesterase (HuAChE) reactivity toward the lethal chemical warfare agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) and its stereoselectivity toward the P(S)-VX enantiomer (VX(S)) were investigated by examining the reactivity of HuAChE and its mutant derivatives toward purified enantiomers of VX and its noncharged isostere O-ethyl S-(3-isopropyl-4-methylpentyl) methylphosphonothioate (nc-VX) as well as echothiophate and its noncharged analogue. Reactivity of wild-type HuAChE toward VX(S) was 115-fold higher than that toward VX(R), with bimolecular rate constants of 1.4 x 10(8) and 1.2 x 10(6) min(-1) M(-1). HuAChE was also 12500-fold more reactive toward VX(S) than toward nc-VX(S). Substitution of the cation binding subsite residue Trp86 with alanine resulted in a 3 order of magnitude decrease in HuAChE reactivity toward both VX enantiomers, while this replacement had an only marginal effect on the reactivity toward the enantiomers of nc-VX and the noncharged echothiophate. These results attest to the critical role played by Trp86 in accommodating the charged moieties of both VX enantiomers. A marked decrease in stereoselectivity toward VX(S) was observed following replacements of Phe295 at the acyl pocket (F295A and F295A/F297A). Replacement of the peripheral anionic site (PAS) residue Asp74 with asparagine (D74N) practically abolished stereoselectivity toward VX(S) (130-fold decrease), while a substitution which retains the negative charge at position 74 (D74E) had no effect. The results from kinetic studies and molecular simulations suggest that the differential reactivity toward the VX enantiomers is mainly a result of a different interaction of the charged leaving group with Asp74.
ESTHER : Ordentlich_2004_Biochemistry_43_11255
PubMedSearch : Ordentlich_2004_Biochemistry_43_11255
PubMedID: 15366935

Title : Poster (21) Analysis of acetylcholinesterase adducts of alzheimer's drugs -
Author(s) : Ordentlich A , Kronman C , Barak D , Ariel N , Kaplan D , Velan B , Shafferman A
Ref : In: Cholinesterases in the Second Millennium: Biomolecular and Pathological Aspects , (Inestrosa NC, Campos EO) P. Universidad Catolica de Chile-FONDAP Biomedicina :332 , 2004
PubMedID:

Title : Poster (23) Phosphorylation and aging of AChE - insights from mutagenesis, mass spectrometry and structural studies -
Author(s) : Barak D , Ordentlich A , Kaplan D , Elhanani E , Segall Y , Barak R , Velan B , Shafferman A
Ref : In: Cholinesterases in the Second Millennium: Biomolecular and Pathological Aspects , (Inestrosa NC, Campos EO) P. Universidad Catolica de Chile-FONDAP Biomedicina :332 , 2004
PubMedID:

Title : Is aromaticity essential for trapping the catalytic histidine 447 in human acetylcholinesterase? - Kaplan_2004_Biochemistry_43_3129
Author(s) : Kaplan D , Barak D , Ordentlich A , Kronman C , Velan B , Shafferman A
Ref : Biochemistry , 43 :3129 , 2004
Abstract : Replacement of both the acyl pocket residue Phe295 as well as residue Phe338, adjacent to the catalytic His447 in human acetylcholinesterase (HuAChE), resulted in a 680-fold decline in catalytic activity due to conformational destabilization of the histidine side chain [Barak et al. (2002) Biochemistry 41, 8245]. A possible restriction of this catalytically nonproductive mobility of His447 in a series of F295X/F338A HuAChEs was examined in silico followed by site-directed mutagenesis. Simulations suggested that of the 12 aliphatic residues substituted at position 295, including hydrophobic and polar amino acids, only methionine was capable of maintaining the catalytically viable conformation of His447. Examination of the reactivities of the actual F295X/F338A HuAChEs showed that indeed the F295M/F338A enzyme was only 2-fold less reactive than the F338A mutant toward acetylthiocholine, while enzymes substituted by the similarly bulky residues leucine and isoleucine were catalytically impaired. Furthermore, only the F295M/F338A enzyme exhibited wild-type-like reactivity toward covalent modifiers of the catalytic Ser203 including the methylphosphonate soman and transition state analogue m-(N,N,N-trimethylammonio)trifluoroacetophenone (TMTFA), as well as a facile dealkylation of the F295M/F338A-soman adduct. A different behavior was observed for bulkier ligands which introduce a deformation in the acyl pocket, and therefore their activity seems only marginally affected by the positioning of His447. The findings emphasize the importance of the precise positioning of His447 for catalysis and indicate that, in the absence of aromatic "trapping", restriction of the histidine mobility in F295X/F338A HuAChEs requires a combination of steric interference and a specific polar interaction. The results also underscore the role of the acyl pocket subsite of cholinesterases in maintaining the catalytically viable conformation of the catalytic histidine.
ESTHER : Kaplan_2004_Biochemistry_43_3129
PubMedSearch : Kaplan_2004_Biochemistry_43_3129
PubMedID: 15023064

Title : The aromatic trapping of the catalytic histidine is essential for efficient catalysis in acetylcholinesterase - Barak_2002_Biochemistry_41_8245
Author(s) : Barak D , Kaplan D , Ordentlich A , Ariel N , Velan B , Shafferman A
Ref : Biochemistry , 41 :8245 , 2002
Abstract : While substitution of the aromatic residues (Phe295, Phe338), located in the vicinity of the catalytic His447 in human acetylcholinesterase (HuAChE) had little effect on catalytic activity, simultaneous replacement of both residues by aliphatic amino acids resulted in a 680-fold decrease in catalytic activity. Molecular simulations suggested that the activity decline is related to conformational destabilization of His447, similar to that observed for the hexamutant HuAChE which mimics the active center of butyrylcholinesterase. On the basis of model structures of other cholinesterases (ChEs), we predicted that catalytically nonproductive mobility of His447 could be restricted by introduction of aromatic residue in a different location adjacent to this histidine (Val407). Indeed, the F295A/F338A/V407F enzyme is 170-fold more reactive than the corresponding double mutant and only 3-fold less reactive than the wild-type HuAChE. However, analogous substitution of Val407 in the hexamutant HuAChE (generating the heptamutant Y72N/Y124Q/W286A/F295L/F297V/Y337A/V407F) did not enhance catalytic activity. Reactivity of these double, triple, hexa, and hepta mutant HuAChEs was monitored toward covalent ligands such as organophosphates and the transition state analogue TMFTA, which probe, respectively, the facility of the enzymes to accommodate Michaelis complexes and to undergo the acylation process. The findings suggest that in the F295A/F338A mutant the two His447 conformational states, which are essential for the different stages of the catalytic process, seem to be destabilized. On the other hand, in the F295A/F338A/V407F mutant only the state involved in acylation is impaired. Such differential effects on the His447 conformational properties demonstrate the general role of aromatic residues in cholinesterases, and probably in other serine hydrolases, in "trapping" of the catalytic histidine and thereby in optimization of catalytic activity.
ESTHER : Barak_2002_Biochemistry_41_8245
PubMedSearch : Barak_2002_Biochemistry_41_8245
PubMedID: 12081473

Title : Does butyrylization of acetylcholinesterase through substitution of the six divergent aromatic amino acids in the active center gorge generate an enzyme mimic of butyrylcholinesterase? - Kaplan_2001_Biochemistry_40_7433
Author(s) : Kaplan D , Ordentlich A , Barak D , Ariel N , Kronman C , Velan B , Shafferman A
Ref : Biochemistry , 40 :7433 , 2001
Abstract : The active center gorge of human acetylcholinesterase (HuAChE) is lined by 14 aromatic residues, whereas in the closely related human butyrylcholinesterase (HuBChE) 3 of the aromatic active center residues (Phe295, Phe297, Tyr337) as well as 3 of the residues at the gorge entrance (Tyr72, Tyr124, Trp286) are replaced by aliphatic amino acids. To investigate whether this structural variability can account for the reactivity differences between the two enzymes, gradual replacement of up to all of the 6 aromatic residues in HuAChE by the corresponding residues in HuBChE was carried out. The affinities of the hexamutant (Y72N/Y124Q/W286A/F295L/F297V/Y337A) toward tacrine, decamethonium, edrophonium, huperzine A, or BW284C51 differed by about 5-, 80-, 170-, 25000-, and 17000-fold, respectively, from those of the wild-type HuAChE. For most of these prototypical noncovalent active center and peripheral site ligands, the hexamutant HuAChE displayed a reactivity phenotype closely resembling that of HuBChE. These results support the accepted view that the active center architectures of AChE and BChE differ mainly by the presence of a larger void space in BChE. Nevertheless, reactivity of the hexamutant HuAChE toward the substrates acetylthiocholine and butyrylthiocholine, or covalent ligands such as phosphonates and the transition state analogue m-(N,N,N-trimethylammonio)trifluoroacetophenone (TMTFA), is about 45-170-fold lower than that of HuBChE. Most of this reduction in reactivity can be related to the combined replacements of the three aromatic residues at the active center, Phe295, Phe297, and Tyr337. We propose that the hexamutant HuAChE, unlike BChE, is impaired in its capacity to accommodate certain tetrahedral species in the active center. This impairment may be related to the enhanced mobility of the catalytic histidine His447, which is observed in molecular dynamics simulations of the hexamutant and the F295L/F297V/Y337A HuAChE enzymes but not in the wild-type HuAChE.
ESTHER : Kaplan_2001_Biochemistry_40_7433
PubMedSearch : Kaplan_2001_Biochemistry_40_7433
PubMedID: 11412096

Title : Resolving pathways of interaction of covalent inhibitors with the active site of acetylcholinesterases: maldi-tof\/ms analysis of various nerve agent phosphyl adducts - Elhanany_2001_Chem.Res.Toxicol_14_912
Author(s) : Elhanany E , Ordentlich A , Dgany O , Kaplan D , Segall Y , Barak R , Velan B , Shafferman A
Ref : Chemical Research in Toxicology , 14 :912 , 2001
Abstract : Understanding reaction pathways of phosphylation, reactivation, and "aging" of AChE with toxic organophosphate compounds is both a biochemical and a pharmacological challenge. Here we describe experiments which allowed to resolve some of the less well understood reaction pathways of phosphylation and "aging" of acetylcholinesterase (AChE) involving phosphoroamidates (P-N agents) such as tabun or the widely used pesticide methamidophos. Tryptic digests of phosphylated AChEs (from human and Torpedo californica), ZipTip peptide fractionation and matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF/MS) enabled reproducible signal enrichment of the isotopically resolved peaks of organophosphoroamidate conjugates of the AChE active site Ser peptides. For tabun and its hexadeuterio analogue, we find, as expected, that the two phosphoramidate adducts of the active site peptide differ by 6.05 mass units but following aging we find that the two corresponding phospho-peptides have identical molecular weights. We further show that the aging product of paraoxon-AChE adduct is identical to the aging product of the tabun-AChE conjugate. These results unequivocally demonstrate that the pathway of aging of tabun adducts of the human or the Torpedo californica AChEs proceeds through P-N bond scission. For methamidophos, we show that phosphylation of AChE involves elimination of the thiomethyl moiety and that the spontaneous reactivation of the resulting organophosphate adduct generates the phosphorus free AChE active site Ser-peptide.
ESTHER : Elhanany_2001_Chem.Res.Toxicol_14_912
PubMedSearch : Elhanany_2001_Chem.Res.Toxicol_14_912
PubMedID: 11453739

Title : Evidence for P-N bond scission in phosphoroamidate nerve agent adducts of human acetylcholinesterase - Barak_2000_Biochemistry_39_1156
Author(s) : Barak D , Ordentlich A , Kaplan D , Barak R , Mizrahi D , Kronman C , Segall Y , Velan B , Shafferman A
Ref : Biochemistry , 39 :1156 , 2000
Abstract : Acetylcholinesterases (AChEs) form conjugates with certain highly toxic organophosphorus (OP) agents that become gradually resistant to reactivation. This phenomenon termed "aging" is a major factor limiting the effectiveness of therapy in certain cases of OP poisoning. While AChE adducts with phosphonates and phosphates are known to age through scission of the alkoxy C-O bond, the aging path for adducts with phosphoroamidates (P-N agents) like the nerve agent N,N-dimethylphosphonocyanoamidate (tabun) is not clear. Here we report that conjugates of tabun and of its butyl analogue (butyl-tabun) with the E202Q and F338A human AChEs (HuAChEs) age at similar rates to that of the wild-type enzyme. This is in marked contrast to the large effect of these substitutions on the aging of corresponding adducts with phosphates and phosphonates, suggesting that a different aging mechanism may be involved. Both tabun and butyl-tabun appear to be similarly accommodated in the active center, as suggested by molecular modeling and by kinetic studies of phosphylation and aging with a series of HuAChE mutants (E202Q, F338A, F295A, F297A, and F295L/F297V). Mass spectrometric analysis shows that HuAChE adduct formation with tabun and butyl-tabun occurs through loss of cyanide and that during the aging process both of these adducts show a mass decrease of 28 +/- 4 Da. Due to the nature of the alkoxy substituent, such mass decrease can be unequivocally assigned to loss of the dimethylamino group, at least for the butyl-tabun conjugate. This is the first demonstration that AChE adducts with toxic P-N agents can undergo aging through scission of the P-N bond.
ESTHER : Barak_2000_Biochemistry_39_1156
PubMedSearch : Barak_2000_Biochemistry_39_1156
PubMedID: 10653663