1
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Nandi NB, Purkayastha A, Roy S, Kłak J, Ganguly R, Alkorta I, Misra TK. Tetranuclear copper( ii) cubane complexes derived from self-assembled 1,3-dimethyl-5-( o-phenolate-azo)-6-aminouracil: structures, non-covalent interactions and magnetic property. NEW J CHEM 2021. [DOI: 10.1039/d0nj05232a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A new doubly opened 4 + 2 Cu4O4 cubane cluster exhibits strong antiferromagnetic exchange coupling with J1 = −110.1 cm−1, and J2 = −27.1 cm−1.
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Affiliation(s)
| | - Atanu Purkayastha
- Department of Chemistry
- National Institute of Technology
- Agartala 799046
- India
| | - Shaktibrata Roy
- Department of Chemistry
- National Institute of Technology
- Agartala 799046
- India
| | - Julia Kłak
- Faculty of Chemistry
- University of Wroclaw
- Wroclaw 50383
- Poland
| | | | - Ibon Alkorta
- Instituto de Química Médica
- CSIC
- 28006 Madrid
- Spain
| | - Tarun Kumar Misra
- Department of Chemistry
- National Institute of Technology
- Agartala 799046
- India
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Miao F, Uchinomiya S, Ni Y, Chang YT, Wu J. Development of pH-Responsive BODIPY Probes for Staining Late Endosome in Live Cells. Chempluschem 2016; 81:1209-1215. [DOI: 10.1002/cplu.201600249] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Revised: 08/08/2016] [Indexed: 11/07/2022]
Affiliation(s)
- Fang Miao
- Department of Chemistry; National University of Singapore; 3 Science Drive 3 Singapore 117543 Singapore
| | - Shohei Uchinomiya
- Department of Pharmaceutical Sciences; Graduate school of Kyushu University; 3-1-1, Maidashi, Higashi-ku Fukuoka 812-8152 Japan
| | - Yong Ni
- Singapore Bioimaging Consortium; Agency for Science, Technology and Research; 11 Biopolis Way, # 02-02 Helios Singapore 138667 Singapore
| | - Young-Tae Chang
- Department of Chemistry; National University of Singapore; 3 Science Drive 3 Singapore 117543 Singapore
- Singapore Bioimaging Consortium; Agency for Science, Technology and Research; 11 Biopolis Way, # 02-02 Helios Singapore 138667 Singapore
| | - Jishan Wu
- Department of Chemistry; National University of Singapore; 3 Science Drive 3 Singapore 117543 Singapore
- Institute of Materials Research and Engineering; A*STAR; 2 Fusionopolis Way, Innovis, #08-03 Singapore 117602 Singapore
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3
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Panteleimonov A, Tkachenko O, Baraban A, Benvenutti EV, Gushikem Y, Kholin Y. Probing Silica—Organic Hybrid Materials Using Small Probes: Simulation of Adsorption Equilibria Influenced by Cooperativity Effects. ADSORPT SCI TECHNOL 2014. [DOI: 10.1260/0263-6174.32.4.305] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Affiliation(s)
- Anton Panteleimonov
- Materials Chemistry Department, V.N. Karazin Kharkiv National University, 4 Svoboda Square, Kharkiv, 61022, Ukraine
- Inorganic Chemistry Department, Institute of Chemistry, State University of Campinas, PO Box 6154, Campinas, SP, 13083-970, Brazil
| | - Oleg Tkachenko
- Materials Chemistry Department, V.N. Karazin Kharkiv National University, 4 Svoboda Square, Kharkiv, 61022, Ukraine
- Inorganic Chemistry Department, Institute of Chemistry, State University of Campinas, PO Box 6154, Campinas, SP, 13083-970, Brazil
| | - Andrey Baraban
- Materials Chemistry Department, V.N. Karazin Kharkiv National University, 4 Svoboda Square, Kharkiv, 61022, Ukraine
| | - Edilson V. Benvenutti
- Laboratory of Solid State Chemistry and Surfaces, Chemistry Institute, Federal University of Rio Grande do Sul, Avenida Bento Goncalves, 9500, Porto Alegre, RS, 91501-970, Brazil
| | - Yoshitaka Gushikem
- Inorganic Chemistry Department, Institute of Chemistry, State University of Campinas, PO Box 6154, Campinas, SP, 13083-970, Brazil
| | - Yuriy Kholin
- Materials Chemistry Department, V.N. Karazin Kharkiv National University, 4 Svoboda Square, Kharkiv, 61022, Ukraine
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Asuero AG, Michałowski T. Comprehensive Formulation of Titration Curves for Complex Acid-Base Systems and Its Analytical Implications. Crit Rev Anal Chem 2011. [DOI: 10.1080/10408347.2011.559440] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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5
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Kholin Y, Zaitsev V. Quantitative physicochemical analysis of equilibria on chemically modified silica surfaces. PURE APPL CHEM 2008. [DOI: 10.1351/pac200880071561] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Quantitative physicochemical analysis (QPCA) enables the determination of the stoichiometric compositions and physicochemical parameters of species in equilibrium systems proceeding from the composition-property dependencies. The paper discusses modifications to the routine QPCA procedures required to characterize properties of reagents fixed on surfaces of silica-organic hybrid materials. The cooperative effects and the energetic heterogeneity of fixed reagents are especially important in this context. It follows that the main peculiarities of silica surfaces chemically modified by aliphatic amines are (a) the pronounced energetic heterogeneity of reagents caused by the non-random surface topography, (b) the decrease of the bacisity of amines induced by their interactions with residual surface silanols, and (c) the expressed sensibility of reactions in the near-surface layer to the state of its hydration. The interaction of grafted organic bases with metal ions results in the preferred formation of bis metal-ligand coordination compounds. Stability constants of complexes are decreased as a consequence of fixation and depend on not only donor but also acceptor ability of a solvent. Also, the denticity of polydentate ligands may decrease as a result of grafting. The changes of protolytic and complexing properties in the case of grafting of weak acids and phosphorus-containing complexons are due to their interactions with other surface groups and the influence of hydration effects in the near-surface layer.
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Affiliation(s)
- Yuriy Kholin
- 1V. Karazin Kharkiv National University, 4 Svoboda Square, Kharkiv, 61077, Ukraine
| | - Vladimir Zaitsev
- 2Kiev National Taras Shevchenko University, 60 Volodymirska Str., Kiev, Ukraine
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6
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Machado M, Rioli V, Dalio F, Castro L, Juliano M, Tersariol I, Ferro E, Juliano L, Oliveira V. The role of Tyr605 and Ala607 of thimet oligopeptidase and Tyr606 and Gly608 of neurolysin in substrate hydrolysis and inhibitor binding. Biochem J 2007; 404:279-88. [PMID: 17313369 PMCID: PMC1868798 DOI: 10.1042/bj20070060] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The physicochemical properties of TOP (thimet oligopeptidase) and NEL (neurolysin) and their hydrolytic activities towards the FRET (fluorescence resonance energy transfer) peptide series Abz-GFSXFRQ-EDDnp [where Abz is o-aminobenzoyl; X=Ala, Ile, Leu, Phe, Tyr, Trp, Ser, Gln, Glu, His, Arg or Pro; and EDDnp is N-(2,4-dinitrophenyl)-ethylenediamine] were compared with those of site-mutated analogues. Mutations at Tyr605 and Ala607 in TOP and at Tyr606 and Gly608 in NEL did not affect the overall folding of the two peptidases, as indicated by their thermal stability, CD analysis and the pH-dependence of the intrinsic fluorescence of the protein. The kinetic parameters for the hydrolysis of substrates with systematic variations at position P1 showed that Tyr605 and Tyr606 of TOP and NEL respectively, played a role in subsite S1. Ala607 of TOP and Gly608 of NEL contributed to the flexibility of the loops formed by residues 600-612 (GHLAGGYDGQYYG; one-letter amino acid codes used) in NEL and 599-611 (GHLAGGYDAQYYG; one-letter amino acid codes used) in TOP contributing to the distinct substrate specificities, particularly with an isoleucine residue at P1. TOP Y605A was inhibited less efficiently by JA-2 {N-[1-(R,S)-carboxy-3-phenylpropyl]Ala-Aib-Tyr-p-aminobenzoate}, which suggested that the aromatic ring of Tyr605 was an important anchor for its interaction with wild-type TOP. The hydroxy groups of Tyr605 and Tyr606 did not contribute to the pH-activity profiles, since the pKs obtained in the assays of mutants TOP Y605F and NEL Y606F were similar to those of wild-type peptidases. However, the pH-kcat/Km dependence curve of TOP Y605A differed from that of wild-type TOP and from TOP Y606F. These results provide insights into the residues involved in the substrate specificities of TOP and NEL and how they select cytosolic peptides for hydrolysis.
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Affiliation(s)
- Maurício F. M. Machado
- *Departamento de Biofísica, Universidade Federal de São Paulo (UNIFESP), 04044-020 São Paulo, SP, Brazil
| | - Vanessa Rioli
- †Laboratório Especial de Toxinologia Aplicada (CAT/CEPID) Instituto Butantan, 05467-010, São Paulo, SP, Brazil
- ‡Departamento de Biologia Celular e Desenvolvimento, Programa de Biologia Celular, Instituto de Ciências Biomédicas, Universidade de São Paulo (USP), 05508-900, São Paulo, SP, Brazil
| | - Fernanda M. Dalio
- §Laboratório de Neurociências, Universidade Cidade de São Paulo, 03071-000, São Paulo, SP, Brazil
| | - Leandro M. Castro
- ‡Departamento de Biologia Celular e Desenvolvimento, Programa de Biologia Celular, Instituto de Ciências Biomédicas, Universidade de São Paulo (USP), 05508-900, São Paulo, SP, Brazil
| | - Maria A. Juliano
- *Departamento de Biofísica, Universidade Federal de São Paulo (UNIFESP), 04044-020 São Paulo, SP, Brazil
| | - Ivarne L. Tersariol
- ∥Centro Interdisciplinar de Investigação Bioquímica (CIIB), Universidade de Mogi das Cruzes, 08780-911, Mogi das Cruzes, SP, Brazil
| | - Emer S. Ferro
- ‡Departamento de Biologia Celular e Desenvolvimento, Programa de Biologia Celular, Instituto de Ciências Biomédicas, Universidade de São Paulo (USP), 05508-900, São Paulo, SP, Brazil
| | - Luiz Juliano
- *Departamento de Biofísica, Universidade Federal de São Paulo (UNIFESP), 04044-020 São Paulo, SP, Brazil
| | - Vitor Oliveira
- *Departamento de Biofísica, Universidade Federal de São Paulo (UNIFESP), 04044-020 São Paulo, SP, Brazil
- §Laboratório de Neurociências, Universidade Cidade de São Paulo, 03071-000, São Paulo, SP, Brazil
- To whom correspondence should be addressed (email )
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Lucho AMS, Panteleimonov AV, Kholin YV, Gushikem Y. Simulation of adsorption equilibria on hybrid materials: Binding of metal chlorides with 3-n-propylpyridinium silsesquioxane chloride ion exchanger. J Colloid Interface Sci 2007; 310:47-56. [PMID: 17316670 DOI: 10.1016/j.jcis.2007.01.035] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2006] [Revised: 01/11/2007] [Accepted: 01/17/2007] [Indexed: 10/23/2022]
Abstract
The quantitative description of cooperativity effects at binding of low-molecular reagents with active reactive centers of hybrid materials requires the elaboration of convenient and reliable meaningful models and calculation procedures. The model of fixed polydentate centers was analyzed as a prospective tool for simulation of adsorption equilibria. The model was shown to be flexible and adaptive. At the theoretic foundations, it is equivalent or more general as compared with another approaches. The procedure for constructing the models fitting the experimental data within their errors and the corresponding calculation tools were discussed. The special attention was paid to the problem of simultaneous determination of sorption capacities and equilibrium constants. To overcome this difficulty the strategy involving the fuzzy sets theory was proposed. The elaborated methods were used to characterize a new material, 3-n-propylpyridinium silsesquioxane chloride ion exchanger. Adsorption of Fe(III), Cu(II), Zn(II), Cd(II), and Hg(II) chlorides by the material from ethanol solutions was studied at 298 K. The material was found to possess a high affinity to metal chlorides. The sorption capacities of the material and the constants of adsorption equilibria were determined. The material demonstrates the following order of affinity: FeCl(3) > CuCl(2), HgCl(2) > CdCl(2) > ZnCl(2). On the base of simulation, the negative cooperativity in the case of the CuCl(2) adsorption was concluded, while adsorption of other chlorides is accompanied by the positive cooperativity.
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Affiliation(s)
- Alzira M S Lucho
- Instituto de Quimica, Universidade Estadual de Campinas, C. Postal 6154, 13084-862 Campinas, SP, Brazil
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Desai PV, Patny A, Gut J, Rosenthal PJ, Tekwani B, Srivastava A, Avery M. Identification of novel parasitic cysteine protease inhibitors by use of virtual screening. 2. The available chemical directory. J Med Chem 2006; 49:1576-84. [PMID: 16509575 DOI: 10.1021/jm0505765] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The incidence of parasitic infections such as malaria, leishmaniasis, and trypanosomiasis has been steadily increasing. Since the existing chemotherapy of these diseases suffers from lack of safe and effective drugs and/or the presence of widespread drug resistance, there is an urgent need for development of potent, mechanism-based antiparasitic agents against these diseases. Cysteine proteases have been established as valid targets for this purpose. The Available Chemical Directory consisting of nearly 355,000 compounds was screened in silico against the homology models of plasmodial cysteine proteases, falcipain-2, and falcipain-3, to identify structurally diverse non-peptide inhibitors. The study led to identification of 22 inhibitors of parasitic cysteine proteases out of which 18 compounds were active against falcipain-2 and falcipain-3. Eight compounds exhibited dual activity against both enzymes. Additionally, four compounds were found to inhibit L. donovani cysteine protease. While one of the cysteine protease inhibitors also exhibited in vitro antiplasmodial activity with an IC50 value of 9.5 microM, others did not show noticeable antiplasmodial activity up to 20 microM. A model identifying important pharmacophoric features common to the structurally diverse falcipain-2 inhibitors has also been developed. Very few potent non-peptide inhibitors of the parasitic cysteine proteases have been reported so far, and identification of these novel and chemically diverse inhibitors should provide leads to be optimized into candidates to treat protozoal infections.
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Affiliation(s)
- Prashant V Desai
- Department of Medicinal Chemistry, School of Pharmacy, P.O. Box 1848, University of Mississippi, University, Mississippi 38677-1848, USA
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Schiaretti F, Bettati S, Viappiani C, Mozzarelli A. pH dependence of tryptophan synthase catalytic mechanism: I. The first stage, the beta-elimination reaction. J Biol Chem 2004; 279:29572-82. [PMID: 15117965 DOI: 10.1074/jbc.m401895200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The pyridoxal 5'-phosphate-dependent beta-subunit of the tryptophan synthase alpha(2)beta(2) complex catalyzes the condensation of L-serine with indole to form L-tryptophan. The first stage of the reaction is a beta-elimination that involves a very fast interconversion of the internal aldimine in a highly fluorescent L-serine external aldimine that decays, via the alpha-carbon proton removal and beta-hydroxyl group release, to the alpha-aminoacrylate Schiff base. This reaction is influenced by protons, monovalent cations, and alpha-subunit ligands that modulate the distribution between open and closed conformations. In order to identify the ionizable residues that might assist catalysis, we have investigated the pH dependence of the rate of the external aldimine decay by rapid scanning UV-visible absorption and single wavelength fluorescence stopped flow. In the pH range 6-9, the reaction was found to be biphasic with the first phase (rate constants k(1)) accounting for more than 70% of the signal change. In the absence of monovalent cations or in the presence of sodium and potassium ions, the pH dependence of k(1) exhibits a bell shaped profile characterized by a pK(a1) of about 6 and a pK(a2) of about 9, whereas in the presence of cesium ions, the pH dependence exhibits a saturation profile characterized by a single pK(a) of 9. The presence of the allosteric effector indole acetylglycine increases the rate of reaction without altering the pH profile and pK(a) values. By combining structural information for the internal aldimine, the external aldimine, and the alpha-aminoacrylate with kinetic data on the wild type enzyme and beta-active site mutants, we have tentatively assigned pK(a1) to betaAsp-305 and pK(a2) to betaLys-87. The loss of pK(a1) in the presence of cesium ions might be due to a shift to lower values, caused by the selective stabilization of a closed form of the beta-subunit.
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Affiliation(s)
- Francesca Schiaretti
- Department of Biochemistry and Molecular Biology, University of Parma, Parma, Italy
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10
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Fornabaio M, Cozzini P, Mozzarelli A, Abraham DJ, Kellogg GE. Simple, intuitive calculations of free energy of binding for protein-ligand complexes. 2. Computational titration and pH effects in molecular models of neuraminidase-inhibitor complexes. J Med Chem 2003; 46:4487-500. [PMID: 14521411 DOI: 10.1021/jm0302593] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
One factor that can strongly influence predicted free energy of binding is the ionization state of functional groups on the ligands and at the binding site at which calculations are performed. This analysis is seldom performed except in very detailed computational simulations. In this work, we address the issues of (i) modeling the complexity resulting from the different ionization states of ligand and protein residues involved in binding, (ii) if, and how, computational methods can evaluate the pH dependence of ligand inhibition constants, and (iii) how to score the protonation-dependent models. We developed a new and fairly rapid protocol called "computational titration" that enables parallel modeling of multiple ionization ensembles for each distinct protonation level. Models for possible protonation combinations for site/ligand ionizable groups are built, and the free energy of interaction for each of them is quantified by the HINT (Hydropathic INTeractions) software. We applied this procedure to the evaluation of the binding affinity of nine inhibitors (six derived from 2,3-didehydro-2-deoxy-N-acetylneuraminic acid, DANA) of influenza virus neuraminidase (NA), a surface glycoprotein essential for virus replication and thus a pharmaceutically relevant target for the design of anti-influenza drugs. The three-dimensional structures of the NA enzyme-inhibitor complexes indicate considerable complexity as the ligand-protein recognition site contains several ionizable moieties. Each computational titration experiment reveals a peak HINT score as a function of added protons. This maximum HINT score indicates the optimum pH (or the optimum protonation state of each inhibitor-protein binding site) for binding. The pH at which inhibition is measured and/or crystals were grown and analyzed can vary from this optimum. A protonation model is proposed for each ligand that reconciles the experimental complex structure with measured inhibition and the free energy of binding. Computational titration methods allow us to analyze the effect of pH in silico and may be helpful in improving ligand binding free energy prediction when protonation or deprotonation of the residues or ligand functional groups at the binding site might be significant.
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Affiliation(s)
- Micaela Fornabaio
- Department of Biochemistry and Molecular Biology, National Institute for the Physics of Matter, University of Parma, 43100 Parma, Italy.
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Wu CY, Lee HJ, Wu SH, Chen ST, Chiou SH, Chang GG. Chemical mechanism of the endogenous argininosuccinate lyase activity of duck lens delta2-crystallin. Biochem J 1998; 333 ( Pt 2):327-34. [PMID: 9657972 PMCID: PMC1219589 DOI: 10.1042/bj3330327] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The endogenous argininosuccinate lyase activity of duck delta2-crystallin was specifically inactivated by the histidine-specific reagent, diethyl pyrocarbonate. The protein was protected by l-citrulline or l-arginine from the diethyl pyrocarbonate inactivation. To characterize further the chemical mechanism of the delta2-crystallin-catalysed reaction, deuterium-labelled argininosuccinate was enzymically synthesized from fumarate and l-arginine with delta2-crystallin in 2H2O. The argininosuccinate synthesized contained about 19% of the anhydride form; however, the deuterium was clearly demonstrated to be incorporated enantioselectively. Only the pro-HR atom at C-9 of the succinate moiety was labelled in the [2H]argininosuccinate-9-d synthesized, which indicates an anti-elimination mechanism for the endogenous argininosuccinate lyase activity of delta2-crystallin. The enzymic activity of duck lens delta2-crystallin in the pH range 5.5-8.5 was investigated using both protium- and deuterium-labelled argininosuccinate as the substrate. From the logkcat versus pH plot, two molecular pKa values of 6.18+/-0.02 and 8.75+/-0.03 were detected in the delta2-crystallin-argininosuccinate binary complex. The former must be dehydronated and the latter hydronated to achieve an optimum reaction rate. The logkcat/Km versus pH plot suggested two molecular pKa values of 5.96+/-0.09 and 8.29+/-0.10 for the free delta2-crystallin to be involved in the substrate binding. Small kinetic isotope effects of 1.17+/-0.02 and 1.05+/-0.09 were found for kcat and kcat/Km respectively. Combining results from labelling and kinetic analysis indicates that the endogenous argininosuccinate lyase activity of duck delta2-crystallin is compatible with a stepwise E1cB mechanism, the rate-limiting step probably at the C-N bond-cleavage step.
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Affiliation(s)
- C Y Wu
- Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Republic of China and Institute of Biochemical Sciences, National Taiwan University, P.O. Box 23-106, Taipei, Republic of China
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12
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Huang TM, Hung HC, Chang TC, Chang GG. Solvent kinetic isotope effects of human placental alkaline phosphatase in reverse micelles. Biochem J 1998; 330 ( Pt 1):267-75. [PMID: 9461520 PMCID: PMC1219137 DOI: 10.1042/bj3300267] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Human placental alkaline phosphatase was embedded in a reverse micellar system prepared by dissolving the surfactant sodium bis(2-ethylhexyl) sulphosuccinate (Aerosol-OT) in 2,2, 4-trimethylpentane. This microemulsion system provides a convenient instrumental tool to study the possible kinetic properties of the membranous enzyme in an immobilized form. The pL (pH/p2H) dependence of hydrolysis of 4-nitrophenyl phosphate has been examined over a pL range of 8.5-12.5 in both aqueous and reverse micellar systems. Profiles of log V versus pL were Ha-bell shaped in the acidic region but reached a plateau in the basic region in which two pKa values of 9.01-9.71 and 9.86-10.48, respectively, were observed in reverse micelles. However, only one pKa value of 9.78-10.27 in aqueous solution was detected. Profiles of log V/K versus pL were bell-shaped in the acidic region. However, they were wave-shaped in the basic region in which a residue of pKa 9.10-9.44 in aqueous solution and 8.07-8.78 in reverse micelles must be dehydronated for the reaction to reach an optimum. The V/K value shifted to a lower value upon dehydronation of a pKa value of 9.80-10.62 in aqueous solution and 11.23-12.17 in reverse micelles. Solvent kinetic isotope effects were measured at three pL values. At pL 9.5, the observed isotope effect was a product of equilibrium isotope effect and a kinetic isotope effect; at pL 10.4, the log V/K value was identical in water and deuterium. The deuterium kinetic isotope effect on V/K was 1.14 in an aqueous solution and 1.16 in reverse micelles. At pL 11.0 at which the log V values reached a plateau in either solvent system, the deuterium kinetic isotope effect on V was 2.08 in an aqueous solution and 0.62 in reverse micelles. Results from a proton inventory experiment suggested that a hydron transfer step is involved in the transition state of the catalytic reaction. The isotopic fractionation factor (pi) for deuterium for the transition state (piT) increased when the pH of the solution was raised. At pL 11.0, the piT was 1.07 in reverse micelles, which corresponds to the inverse-isotope effect of the reaction in this solvent system. Normal viscosity effects on kcat and kcat/Km were observed in aqueous solution, corresponding to a diffusional controlled physical step as the rate-limiting step. We propose that the rate-limiting step of the hydrolytic reaction changes from phosphate releasing in aqueous solution to a covalent phosphorylation or dephosphorylation step in reverse micelles.
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Affiliation(s)
- T M Huang
- Graduate Institutes of Biochemistry and Life Sciences, National Defense Medical Centre, Taipei, Taiwan, Republic of China
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Zographos SE, Oikonomakos NG, Dixon HB, Griffin WG, Johnson LN, Leonidas DD. Sulphate-activated phosphorylase b: the pH-dependence of catalytic activity. Biochem J 1995; 310 ( Pt 2):565-70. [PMID: 7654195 PMCID: PMC1135932 DOI: 10.1042/bj3100565] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The pH-dependence of sulphate-activated phosphorylase b has been studied in the direction of glycogen synthesis. The bell-shaped curve of the pH-dependence of the catalytic constant for the AMP-activated enzyme showed pK values of 6.1 and 7.3, but the curve for the enzyme activated by 0.9 M ammonium sulphate showed a drop of activity on the acid side at much higher pH values. Its bell was centred at pH 7.8 but it was too narrow to be characterized by only two pK values. The narrowness of the curve could be explained by positive co-operativity, but not its unusually steep acid side. We suggest that the fall on the acid side is due to more than one hydronation (addition of H+). The points can be fitted by a curve with two de-activating hydronations and a de-activating dehydronation having identical titration pK values of 7.5, and hence molecular values of 7.0, 7.5 and 8.0. If both 0.9 M ammonium sulphate and 5 mM AMP are added, the bell is as broad as with AMP alone, but is somewhat raised in pH optimum. The results are discussed in the light of new structural data from crystallographic studies on binary complexes of the enzyme.
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Affiliation(s)
- S E Zographos
- Institute of Biological Research and Biotechnology, National Hellenic Research Foundation, Athens, Greece
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Dixon HB. Part of the phospho group of pyridoxal phosphate may titrate over the pH range 5-8 in aspartate aminotransferase. Biochem J 1991; 280 ( Pt 3):832-3. [PMID: 1764047 PMCID: PMC1130534 DOI: 10.1042/bj2800832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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