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Abstract
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Enzymes
are essential for all living organisms, and their effectiveness as
chemical catalysts has driven more than a half century of research
seeking to understand the enormous rate enhancements they provide.
Nevertheless, a complete understanding of the factors that govern
the rate enhancements and selectivities of enzymes remains elusive,
due to the extraordinary complexity and cooperativity that are the
hallmarks of these biomolecules. We have used a combination of site-directed
mutagenesis, pre-steady-state kinetics, X-ray crystallography, nuclear
magnetic resonance (NMR), vibrational and fluorescence spectroscopies,
resonance energy transfer, and computer simulations to study the implications
of conformational motions and electrostatic interactions on enzyme
catalysis in the enzyme dihydrofolate reductase (DHFR). We have
demonstrated that modest equilibrium conformational changes are functionally
related to the hydride transfer reaction. Results obtained for mutant
DHFRs illustrated that reductions in hydride transfer rates are correlated
with altered conformational motions, and analysis of the evolutionary
history of DHFR indicated that mutations appear to have occurred to
preserve both the hydride transfer rate and the associated conformational
changes. More recent results suggested that differences in local electrostatic
environments contribute to finely tuning the substrate pKa in the initial protonation step. Using a combination
of primary and solvent kinetic isotope effects, we demonstrated that
the reaction mechanism is consistent across a broad pH range, and
computer simulations suggested that deprotonation of the active site
Tyr100 may play a crucial role in substrate protonation at high pH. Site-specific incorporation of vibrational thiocyanate probes into
the ecDHFR active site provided an experimental tool
for interrogating these microenvironments and for investigating changes
in electrostatics along the DHFR catalytic cycle. Complementary molecular
dynamics simulations in conjunction with mixed quantum mechanical/molecular
mechanical calculations accurately reproduced the vibrational frequency
shifts in these probes and provided atomic-level insight into the
residues influencing these changes. Our findings indicate that conformational
and electrostatic changes are intimately related and functionally
essential. This approach can be readily extended to the study of other
enzyme systems to identify more general trends in the relationship
between conformational fluctuations and electrostatic interactions.
These results are relevant to researchers seeking to design novel
enzymes as well as those seeking to develop therapeutic agents that
function as enzyme inhibitors.
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Affiliation(s)
- Philip Hanoian
- Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - C. Tony Liu
- Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Sharon Hammes-Schiffer
- Department
of Chemistry, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
| | - Stephen Benkovic
- Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802, United States
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Fang Y, French J, Zhao H, Benkovic S. G-protein-coupled receptor regulation of de novo purine biosynthesis: a novel druggable mechanism. Biotechnol Genet Eng Rev 2014; 29:31-48. [PMID: 24568251 DOI: 10.1080/02648725.2013.801237] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Spatial organization of metabolic enzymes may represent a general cellular mechanism to regulate metabolic flux. One recent example of this type of cellular phenomenon is the purinosome, a newly discovered multi-enzyme metabolic assembly that includes all of the enzymes within the de novo purine biosynthetic pathway. Our understanding of the components and regulation of purinosomes has significantly grown in recent years. This paper reviews the purine de novo biosynthesis pathway and its regulation, and presents the evidence supporting the purinosome assembly and disassembly processes under the control of G-protein-coupled receptor (GPCR) signaling. This paper also discusses the implications of purinosome and GPCR regulation in drug discovery.
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Affiliation(s)
- Ye Fang
- a Biochemical Technologies, Science and Technology Division , Corning Incorporated , Corning , New York , USA
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3
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Abstract
In most organisms, clamp loaders catalyze both the loading of sliding clamps onto DNA and their removal. How these opposing activities are regulated during assembly of the DNA polymerase holoenzyme remains unknown. By utilizing FRET to monitor protein-DNA interactions, we examined assembly of the human holoenzyme. The results indicate that assembly proceeds in a stepwise manner. The clamp loader (RFC) loads a sliding clamp (PCNA) onto a primer/template junction but remains transiently bound to the DNA. Unable to slide away, PCNA re-engages with RFC and is unloaded. In the presence of polymerase (polδ), loaded PCNA is captured from DNA-bound RFC which subsequently dissociates, leaving behind the holoenzyme. These studies suggest that the unloading activity of RFC maximizes the utilization of PCNA by inhibiting the build-up of free PCNA on DNA in the absence of polymerase and recycling limited PCNA to keep up with ongoing replication. DOI:http://dx.doi.org/10.7554/eLife.00278.001.
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Affiliation(s)
- Mark Hedglin
- Department of Chemistry, The Pennsylvania State University, University Park, United States
| | - Senthil K Perumal
- Department of Chemistry, The Pennsylvania State University, University Park, United States
| | - Zhenxin Hu
- Department of Chemistry, The Pennsylvania State University, University Park, United States
| | - Stephen Benkovic
- Department of Chemistry, The Pennsylvania State University, University Park, United States
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4
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Lee TH, Benkovic S, Mishra P, Kumar R. Mechanism of Yeast Clamp Loading on DNA. Biophys J 2011. [DOI: 10.1016/j.bpj.2010.12.1525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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5
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Croquette V, Manosas M, Ding F, Spiering M, Benkovic S. Forward and Backward Motion of Replicative Polymerases and Their Coupling with the Helicase. Biophys J 2011. [DOI: 10.1016/j.bpj.2010.12.3055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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6
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Schray K, Benkovic S. Additions and Correcitons - Mechanisms of Hydrolysis of Phosphate Ester Derivatives of Phosphoenolpyruvic Acid. J Am Chem Soc 2004. [DOI: 10.1021/ja00749a606] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
The use of emissions trading (cap and trade) is gaining worldwide recognition as an extremely effective policy tool. The U.S. Sulfur Dioxide (SO2) Emissions Trading Program has achieved an unprecedented level of environmental protection in a cost-effective manner. The successful results of the program have led domestic and foreign governments to consider the application of cap and trade to address other air quality issues. Certain analyses are particularly important in determining whether or not cap and trade is an appropriate policy tool. This paper offers a set of questions that can be used as criteria for determining whether or not cap and trade is the preferred policy approach to an environmental problem.
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Affiliation(s)
- S Benkovic
- United States Environmental Protection Agency, Washington, DC 20460, USA.
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Pennypacker KR, Yang X, Gordon MN, Benkovic S, Miller D, O'Callaghan JP. Long-term induction of Fos-related antigen-2 after methamphetamine-, methylenedioxymethamphetamine-, 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine- and trimethyltin-induced brain injury. Neuroscience 2001; 101:913-9. [PMID: 11113340 DOI: 10.1016/s0306-4522(00)00381-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
A long-term induction of Fos-related antigens has been shown in neurons after brain injury, suggesting that Fos-related antigens are involved in enhancing the transcription of genes related to the process of regeneration and repair. In the present study, we report that levels of Fos-related antigen-2 are elevated in several models of chemically induced brain injury. Trimethyltin, which causes degeneration of neurons primarily in the hippocampus and other limbic regions, results in a five-fold induction of Fos-related antigen-2 immunoreactivity in neurons in the pyramidal and dentate layers of the hippocampus starting at seven days post-treatment and persisting for 60days. Methamphetamine and methylenedioxymethamphetamine, agents which cause degeneration of dopaminergic nerve terminals in the striatum of the mouse, cause an increase in Fos-related antigen-2 immunoreactivity which begins at three days post-treatment and returns to basal levels by days 5 and 15, respectively. Treatment with 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine elevated levels of Fos-related antigen-2 in the mouse striatum at three days post-treatment. This abbreviated time-course of Fos-related antigen-2 induction is consistent with less severe insult (terminal damage) relative to trimethyltin (cell death), but induction occurs during the period of regeneration and repair in both models. Dexfenfluramine, a non-neurotoxic amphetamine, does not induce Fos-related antigen-2 expression. Decreasing core temperature of the mouse, which blocks amphetamine-induced neurotoxicity, also blocks Fos-related antigen-2 induction. In summary, Fos-related antigen-2 is induced in models of both cell death and terminal degeneration, suggesting that this transcription factor may serve as a universal signal transduction molecule involved in the regulation of genes related to regeneration and repair in the CNS.
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Affiliation(s)
- K R Pennypacker
- University of South Florida, College of Medicine, Department of Pharmacology and Therapeutics, Tampa, FL 33612, USA.
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Pennypacker KR, Hernandez H, Benkovic S, Morgan DG, Willing AE, Sanberg PR. Induction of presenilins in the rat brain after middle cerebral arterial occlusion. Brain Res Bull 1999; 48:539-43. [PMID: 10372515 DOI: 10.1016/s0361-9230(99)00031-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In the present study, we have examined the expression of both presenilins in the rat hippocampus, cortex, striatum, and cerebellum after middle cerebral artery occlusion (MCA-O), an animal model of ischemia. The cortex showed the greatest increase in PS mRNA levels (7-10-fold) at 4 and 8 days posttreatment. Presenilin-1 (PS-1) levels in the contralateral cortex were significantly increased 1 day after MCA-O. In comparison, PS mRNA content was only modestly elevated in the hippocampus and striatum at 4 and 8 days after MCA-O (30-100% changes). Other Alzheimer's disease (AD)-related genes, amyloid precursor protein and apolipoprotein E, are induced in brain injury suggesting that these AD-related genes may well be components of a brain-injury response. Thus, a breakdown in this response via cerebrovascular disease and/or genetic mutation may contribute to AD pathology.
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Affiliation(s)
- K R Pennypacker
- Department of Pharmacology and Therapeutics, University of South Florida, College of Medicine, Tampa 33612, USA.
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Holcomb L, Gordon MN, McGowan E, Yu X, Benkovic S, Jantzen P, Wright K, Saad I, Mueller R, Morgan D, Sanders S, Zehr C, O'Campo K, Hardy J, Prada CM, Eckman C, Younkin S, Hsiao K, Duff K. Accelerated Alzheimer-type phenotype in transgenic mice carrying both mutant amyloid precursor protein and presenilin 1 transgenes. Nat Med 1998; 4:97-100. [PMID: 9427614 DOI: 10.1038/nm0198-097] [Citation(s) in RCA: 956] [Impact Index Per Article: 36.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Genetic causes of Alzheimer's disease (AD) include mutations in the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2) genes. The mutant APP(K670N,M671L) transgenic line, Tg2576, shows markedly elevated amyloid beta-protein (A beta) levels at an early age and, by 9-12 months, develops extracellular AD-type A beta deposits in the cortex and hippocampus. Mutant PS1 transgenic mice do not show abnormal pathology, but do display subtly elevated levels of the highly amyloidogenic 42- or 43-amino acid peptide A beta42(43). Here we demonstrate that the doubly transgenic progeny from a cross between line Tg2576 and a mutant PS1M146L transgenic line develop large numbers of fibrillar A beta deposits in cerebral cortex and hippocampus far earlier than their singly transgenic Tg2576 littermates. In the period preceding overt A beta deposition, the doubly transgenic mice show a selective 41% increase in A beta42(43) in their brains. Thus, the development of AD-like pathology is substantially enhanced when a PS1 mutation, which causes a modest increase in A beta42(43), is introduced into Tg2576-derived mice. Remarkably, both doubly and singly transgenic mice showed reduced spontaneous alternation performance in a "Y" maze before substantial A beta deposition was apparent. This suggests that some aspects of the behavioral phenotype in these mice may be related to an event that precedes plaque formation.
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Affiliation(s)
- L Holcomb
- Department of Pharmacology, University of South Florida, Tampa 33612, USA
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Abstract
Combinatorial libraries are a promising alternative for isolating catalytic antibodies produced by the immune system in response to the transition-state analog of a given reaction. Large, diverse panels of antibodies with high affinity for the transition-state analog can be isolated using screening or selection approaches. Furthermore, we have estimated that nucleotide sequences that bear close similarity to the sequence for a known catalytic antibody occur in combination at frequencies sufficient for their detection in such libraries.
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Affiliation(s)
- B Posner
- Department of Chemistry, Pennsylvania State University, University Park 16802
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12
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Gopalakrishnan V, Benkovic S. Effect of a thiobenzimidazolone derivative on DNA strand transfer catalyzed by HIV-1 reverse transcriptase. J Biol Chem 1994; 269:4110-5. [PMID: 7508439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Thiobenzimidazolone (TIBO) derivatives are known inhibitors of the DNA polymerase activity of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). The effect of a TIBO derivative ((+)-S-4,5,6,7-tetrahydro-9-chloro-5- methyl-6-(3-methyl-2-butenyl)-imidazol[4,5,1-jk]1,4-benzodiazapine -2-thione ) on the DNA strand transfer reaction catalyzed by HIV-1 RT (which is a function of both the DNA polymerase and RNase H activities) was investigated by delineating the effect of the drug on the constitutive DNA polymerase and RNase H activities) was investigated by delineating the effect of the drug on the constitutive DNA polymerase and RNase H activities. Single nucleotide incorporation on template-primer 1 was used to study the DNA polymerase activity of HIV-1 RT while template-primer 2 was used to study the effect of TIBO on the RNase H activity (polymerase independent). The drug was found to decrease the amplitude of the presteady-state burst when preequilibrated with the enzyme-substrate complex besides decreasing the steady-state rate of single nucleotide incorporations. In the absence of preincubation, TIBO did not affect the burst amplitude but decreased the steady-state rate after the pre-transient phase. This suggested that binding of TIBO to RT was affected by the presence of template-primer and required dissociation of the enzyme from the template-primer for effective binding. The polymerase-independent RNase H activity was activated in the presence of TIBO. The effect of TIBO on the overall process of DNA strand transfer is a balance between its inhibition of the polymerase activity and its activation of the RNase H activity.
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Affiliation(s)
- V Gopalakrishnan
- Department of Chemistry, Pennsylvania State University, University Park 16802
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13
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Bartlett WP, Li XS, Williams M, Benkovic S. Localization of insulin-like growth factor-1 mRNA in murine central nervous system during postnatal development. Dev Biol 1991; 147:239-50. [PMID: 1879610 DOI: 10.1016/s0012-1606(05)80021-1] [Citation(s) in RCA: 119] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Insulin-like growth factor-1 (IGF-1) is believed to play a role in the regulation of brain growth. The identity of cells responsible for its synthesis in the immature brain, however, has not been established. To identify potential sites of IGF-1 synthesis, in situ hybridization has been utilized to localize IGF-1 mRNA in the murine brain during the first postnatal month. Although IGF-1 mRNA was detected in all regions of the neonatal brain, there was considerable regional variation in the level of expression. Neurons were the principle sites IGF-1 mRNA expression and expression was typically restricted to one or two neuronal cell types within each region. In the cerebellar cortex, for example, only Purkinje cells hybridized to the IGF-1 probe. In contrast to gray matter, IGF-1 labeled cells were rarely found in presumptive white matter tracts of the forebrain. The hybridization signal was most prominent in regions where neurogenesis persisted after birth, including the cerebellum, olfactory bulb, and hippocampal complex. The timing of IGF-1 mRNA expression appeared to be temporally related to local neuronal proliferation. The number of labeled cells and intensity of hybridization signal was greatest during the first 2 postnatal weeks, a period of rapid neuronal proliferation in these regions. At the end of the first month, when neurogenesis had essentially ceased, IGF-1 signal strength had declined to background levels. The temporal and spatial pattern IGF-1 mRNA expression in the immature CNS was consistent with a role for locally produced IGF-1 in the regulation of brain development.
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Affiliation(s)
- W P Bartlett
- Department of Neuroscience and Anatomy, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033
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Benkovic S, Kenyon G, Wold F, poulter C, Stubbe J, Krantz A, Gresser A, Kluger R, Sanchez E. Abstracts, Division of Biological Chemistry, 3rd Chemical Congress of North America and 195th National Meeting of the American Chemical Society, June 5 - 10, 1988. Biochemistry 1988. [DOI: 10.1021/bi00408a600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Benkovic S, Peisach J, Gorenstein D, Poulter C. Abstracts, Division of Biological Chemistry, 194th National Meeting of the American Chemical Society, August 30 - September 4, 1987. Biochemistry 1987. [DOI: 10.1021/bi00387a600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Maryanoff B, Reitz A, Tutwiler G, Benkovic S, Benkovic P, Pilkis S. Additions and Corrections - Stereoselective Synthesis and Biological Activity of β -and α-D-Arabinose 1,5-Diphosphate: Analogues of a Potent Metabolic Regulator. J Am Chem Soc 1985. [DOI: 10.1021/ja00303a602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Benkovic P, Hegazi M, Cunningham B, Benkovic S. Corrections - Investigation of the Pre-Steady-State Kinetics of Fructose Biphosphatase by Employment of an Indicator Method. Biochemistry 1979. [DOI: 10.1021/bi00586a612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Steffens J, Siewers I, Benkovic S. Corections - Catalysis of Phosphoryl Group Transfer. The Role of Divalent Metal Ions in the Hydrolysis of Lactic Acid O-Phenyl Phosphate and Salicylic Acid O-Aryl Phosphates. Biochemistry 1976. [DOI: 10.1021/bi00649a600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Farina P, Farina L, Benkovic S. Additions and Corrections - Stereoselective Chemical Reduction of 5,10-Methenyltetrahydrofolate. J Am Chem Soc 1975. [DOI: 10.1021/ja00847a601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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