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Qin Y, Ke W, Faheem A, Ye Y, Hu Y. A rapid and naked-eye on-site monitoring of biogenic amines in foods spoilage. Food Chem 2023; 404:134581. [DOI: 10.1016/j.foodchem.2022.134581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2022] [Revised: 09/17/2022] [Accepted: 10/08/2022] [Indexed: 11/22/2022]
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2
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Qin Y, Faheem A, Hu Y. A spore-based portable kit for on-site detection of fluoride ions. JOURNAL OF HAZARDOUS MATERIALS 2021; 419:126467. [PMID: 34182423 DOI: 10.1016/j.jhazmat.2021.126467] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Revised: 06/16/2021] [Accepted: 06/21/2021] [Indexed: 06/13/2023]
Abstract
The excess residues of fluoride ions cause serious human health problems, making their detection highly valuable. In this work, a whole-cell-based biosensor was presented for the detection of fluoride ions, which can inhibit the color reaction of 3,3',5,5',-tetramethylbenzidine (TMB) catalyzed by the CotA-laccase of spore surface. This reaction for the detection of fluoride ions could be read out through UV-vis spectrophotometer, smartphone, or standard colorimetric card within 10 min. Under optimum conditions, a linear range of 1-600 μmol L-1 with a detection limit of 0.12 μmol L-1 (3σ/k) was achieved for fluoride ions detection by using UV-vis spectrophotometer. The biosensor coupling with smartphone had a good linear response to fluoride ions concentration in the range of 5-600 μmol L-1 with LOD of 0.90 μmol L-1 (3σ/k). The standard colorimetric card can be directly used for recognizing the fluoride ions level via naked-eyes. A portable kit based on a colorimetric card and smartphone was developed and has been successfully applied for fluoride ions monitoring in surface waters and groundwater. This developed method has several advantages such as rapid, outstanding selectivity and anti-interference, low-cost, ease of operation and storage, and eco-friendliness, meeting the demands of point-of-care testing of fluoride ions and disease prevention.
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Affiliation(s)
- Yuqing Qin
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China
| | - Aroosha Faheem
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China
| | - Yonggang Hu
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China.
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3
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Kembaren R, Fokkink R, Westphal AH, Kamperman M, Kleijn JM, Borst JW. Balancing Enzyme Encapsulation Efficiency and Stability in Complex Coacervate Core Micelles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:8494-8502. [PMID: 32598154 PMCID: PMC7467766 DOI: 10.1021/acs.langmuir.0c01073] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Revised: 06/29/2020] [Indexed: 06/11/2023]
Abstract
Encapsulation of charged proteins into complex coacervate core micelles (C3Ms) can be accomplished by mixing them with oppositely charged diblock copolymers. However, these micelles tend to disintegrate at high ionic strength. Previous research showed that the addition of a homopolymer with the same charge sign as the protein improved the stability of protein-containing C3Ms. In this research, we used fluorescence correlation spectroscopy (FCS) and dynamic light scattering (DLS) to study how the addition of the homopolymer affects the encapsulation efficiency and salt stability of the micelles. We studied the encapsulation of laccase spore coat protein A (CotA), a multicopper oxidase, using a strong cationic-neutral diblock copolymer, poly(N-methyl-2-vinyl-pyridinium iodide)-block-poly(ethylene oxide) (PM2VP128-b-PEO477), and a negatively charged homopolymer, poly(4-styrenesulfonate) (PSS215). DLS indeed showed an improved stability of this three-component C3M system against the addition of salt compared to a two-component system. Remarkably, FCS showed that the release of CotA from a three-component C3M system occurred at a lower salt concentration and over a narrower concentration range than the dissociation of C3Ms. In conclusion, although the addition of the homopolymer to the system leads to micelles with a higher salt stability, CotA is excluded from the C3Ms already at lower ionic strengths because the homopolymer acts as a competitor of the enzyme for encapsulation.
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Affiliation(s)
- Riahna Kembaren
- Physical
Chemistry and Soft Matter, Wageningen University
and Research, Stippeneng 4, 6708 WE Wageningen, the Netherlands
- Laboratory
of Biochemistry, Microspectroscopy Research Facility, Wageningen University and Research, Stippeneng 4, 6708
WE Wageningen, Netherlands
| | - Remco Fokkink
- Physical
Chemistry and Soft Matter, Wageningen University
and Research, Stippeneng 4, 6708 WE Wageningen, the Netherlands
| | - Adrie H. Westphal
- Laboratory
of Biochemistry, Microspectroscopy Research Facility, Wageningen University and Research, Stippeneng 4, 6708
WE Wageningen, Netherlands
| | - Marleen Kamperman
- Zernike
Institute for Advanced Research, University
of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands
| | - J. Mieke Kleijn
- Physical
Chemistry and Soft Matter, Wageningen University
and Research, Stippeneng 4, 6708 WE Wageningen, the Netherlands
| | - Jan Willem Borst
- Laboratory
of Biochemistry, Microspectroscopy Research Facility, Wageningen University and Research, Stippeneng 4, 6708
WE Wageningen, Netherlands
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4
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Valles M, Kamaruddin AF, Wong LS, Blanford CF. Inhibition in multicopper oxidases: a critical review. Catal Sci Technol 2020. [DOI: 10.1039/d0cy00724b] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
This review critiques the literature on inhibition of O2-reduction catalysis in multicopper oxidases like laccase and bilirubin oxidase and provide recommendations for best practice when carrying out experiments and interpreting published data.
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Affiliation(s)
- Morgane Valles
- Manchester Institute of Biotechnology
- University of Manchester
- Manchester
- UK
- Department of Chemistry
| | - Amirah F. Kamaruddin
- Manchester Institute of Biotechnology
- University of Manchester
- Manchester
- UK
- Department of Materials
| | - Lu Shin Wong
- Manchester Institute of Biotechnology
- University of Manchester
- Manchester
- UK
- Department of Chemistry
| | - Christopher F. Blanford
- Manchester Institute of Biotechnology
- University of Manchester
- Manchester
- UK
- Department of Materials
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5
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Lee S, Kang M, Bae JH, Sohn JH, Sung BH. Bacterial Valorization of Lignin: Strains, Enzymes, Conversion Pathways, Biosensors, and Perspectives. Front Bioeng Biotechnol 2019; 7:209. [PMID: 31552235 PMCID: PMC6733911 DOI: 10.3389/fbioe.2019.00209] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 08/19/2019] [Indexed: 12/17/2022] Open
Abstract
Lignin, an aromatic polymer found in plants, has been studied for years in many biological fields. Initially, when biofuel was produced from lignocellulosic biomass, lignin was regarded as waste generated by the biorefinery and had to be removed, because of its inhibitory effects on fermentative bacteria. Although it has since proven to be a natural resource for bio-products with considerable potential, its utilization is confined by its complex structure. Hence, the microbial degradation of lignin has attracted researchers' interest to overcome this problem. From this perspective, the studies have primarily focused on fungal systems, such as extracellular peroxidase and laccase from white- and brown-rot fungi. However, recent reports have suggested that bacteria play an increasing role in breaking down lignin. This paper, therefore, reviews the role of bacteria in lignin and lignin-related research. Several reports on bacterial species in soil that can degrade lignin and their enzymes are included. In addition, a cellulolytic anaerobic bacterium capable of solubilizing lignin and carbohydrate simultaneously has recently been identified, even though the enzyme involved has not been discovered yet. The assimilation of lignin-derived small molecules and their conversion to renewable chemicals by bacteria, such as muconic acid and polyhydroxyalkanoates, including genetic modification to enhance their capability was discussed. This review also covers the indirect use of bacteria for lignin degradation, which is concerned with whole-cell biosensors designed to detect the aromatic chemicals released from lignin transformation.
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Affiliation(s)
- Siseon Lee
- Synthetic Biology and Bioengineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea
| | - Minsik Kang
- Synthetic Biology and Bioengineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea
- Department of Biosystems and Bioengineering, Korea University of Science and Technology, Daejeon, South Korea
| | - Jung-Hoon Bae
- Synthetic Biology and Bioengineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea
| | - Jung-Hoon Sohn
- Synthetic Biology and Bioengineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea
- Department of Biosystems and Bioengineering, Korea University of Science and Technology, Daejeon, South Korea
| | - Bong Hyun Sung
- Synthetic Biology and Bioengineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea
- Department of Biosystems and Bioengineering, Korea University of Science and Technology, Daejeon, South Korea
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6
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Zhang Y, Lv Z, Zhou J, Fang Y, Wu H, Xin F, Zhang W, Ma J, Xu N, He A, Dong W, Jiang M. Amperometric Biosensors Based on Recombinant Bacterial Laccase CotA for Hydroquinone Determination. ELECTROANAL 2019. [DOI: 10.1002/elan.201900395] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Yue Zhang
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
| | - Ziyao Lv
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
| | - Jie Zhou
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
| | - Yan Fang
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
| | - Hao Wu
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM)Nanjing Tech University Nanjing 211800 P.R. China
| | - Fengxue Xin
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM)Nanjing Tech University Nanjing 211800 P.R. China
| | - Wenming Zhang
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM)Nanjing Tech University Nanjing 211800 P.R. China
| | - Jiangfeng Ma
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM)Nanjing Tech University Nanjing 211800 P.R. China
| | - Ning Xu
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
- Jiangsu Key Laboratory for Biomass-based Energy and Enzyme TechnologyHuaiyin Normal University Huaian 223300 P.R. China
| | - Aiyong He
- Jiangsu Key Laboratory for Biomass-based Energy and Enzyme TechnologyHuaiyin Normal University Huaian 223300 P.R. China
| | - Weiliang Dong
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM)Nanjing Tech University Nanjing 211800 P.R. China
| | - Min Jiang
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical EngineeringNanjing Tech University Nanjing 211800 P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM)Nanjing Tech University Nanjing 211800 P.R. China
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Lopes P, Koschorreck K, Nedergaard Pedersen J, Ferapontov A, Lörcher S, Skov Pedersen J, Urlacher VB, Ferapontova EE. Bacillus Licheniformis
CotA Laccase Mutant: ElectrocatalyticReduction of O
2
from 0.6 V (SHE) at pH 8 and in Seawater. ChemElectroChem 2019. [DOI: 10.1002/celc.201900363] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Paula Lopes
- Interdisciplinary Nanoscience Center, iNANOAarhus University Gustav Wieds Vej 14 8000 Aarhus Denmark
- Current address: Gent University Zwijnaard 126 9052 Belgium
| | - Katja Koschorreck
- Institute of BiochemistryHeinrich-Heine University Düsseldorf Universitätsstrasse 1 40225 Düsseldorf Germany
| | | | | | - Samuel Lörcher
- Interdisciplinary Nanoscience Center, iNANOAarhus University Gustav Wieds Vej 14 8000 Aarhus Denmark
- Current address: Universitaet Basel 4056 Basel Switzerland
| | - Jan Skov Pedersen
- Interdisciplinary Nanoscience Center, iNANOAarhus University Gustav Wieds Vej 14 8000 Aarhus Denmark
- Department of ChemistryAarhus University 8000 Aarhus Denmark
| | - Vlada B. Urlacher
- Institute of BiochemistryHeinrich-Heine University Düsseldorf Universitätsstrasse 1 40225 Düsseldorf Germany
| | - Elena E. Ferapontova
- Interdisciplinary Nanoscience Center, iNANOAarhus University Gustav Wieds Vej 14 8000 Aarhus Denmark
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8
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Alba-Molina D, Rodríguez-Padrón D, Puente-Santiago AR, Giner-Casares JJ, Martín-Romero MT, Camacho L, Martins LO, Muñoz-Batista MJ, Cano M, Luque R. Mimicking the bioelectrocatalytic function of recombinant CotA laccase through electrostatically self-assembled bioconjugates. NANOSCALE 2019; 11:1549-1554. [PMID: 30629067 DOI: 10.1039/c8nr06001k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Unprecedented 3D nanobiosystems composed of recombinant CotA laccases and citrate-stabilised gold nanoparticles have been successfully achieved by an electrostatic self-assembly strategy. The bioelectrochemical reduction of O2 driven by CotA laccase at the spore coat was mimicked. Consequently key insights into its bioelectrocatalytic function were unravelled.
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Affiliation(s)
- David Alba-Molina
- Departamento de Química Física y Termodinamica Aplicada, Instituto Universitario de Investigación en Química Fina y Nanoquímica IUIQFN, Facultad de Ciencias, Universidad de Córdoba, Campus de Rabanales, Ed. Marie Curie, E-14071 Córdoba, Spain.
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9
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Application of eukaryotic and prokaryotic laccases in biosensor and biofuel cells: recent advances and electrochemical aspects. Appl Microbiol Biotechnol 2018; 102:10409-10423. [PMID: 30327832 DOI: 10.1007/s00253-018-9421-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 09/25/2018] [Accepted: 09/26/2018] [Indexed: 12/25/2022]
Abstract
Laccases exhibit a wide range of applications, especially in the electrochemical field, where they are regarded as a potential biotic component. Laccase-based biosensors have immense practical applications in the food, environmental, and medical fields. The application of laccases as biocathodes in enzymatic biofuel cells has promising potential in the preparation of implantable equipment. Extensive studies have been directed towards the potential role of fungal laccases as biotic components of electrochemical equipment. In contrast, the potential of prokaryotic laccases in electrochemistry has been not fully understood. However, there has been recent and rapid progress in the discovery and characterization of new types of prokaryotic laccases. In this review, we have comprehensively discussed the application of different sources of laccases as a biocatalytic component in various fields of application. Further, we described the potential of different types of laccases in bioelectrochemical applications.
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10
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Affiliation(s)
- Nicolas Mano
- CNRS, CRPP, UPR 8641, 33600 Pessac, France
- University of Bordeaux, CRPP, UPR 8641, 33600 Pessac, France
| | - Anne de Poulpiquet
- Aix Marseille Univ., CNRS, BIP, 31, chemin Aiguier, 13402 Marseille, France
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11
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Martins LO, Durão P, Brissos V, Lindley PF. Laccases of prokaryotic origin: enzymes at the interface of protein science and protein technology. Cell Mol Life Sci 2015; 72:911-22. [PMID: 25572294 PMCID: PMC11113980 DOI: 10.1007/s00018-014-1822-x] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Accepted: 12/30/2014] [Indexed: 10/24/2022]
Abstract
The ubiquitous members of the multicopper oxidase family of enzymes oxidize a range of aromatic substrates such as polyphenols, methoxy-substituted phenols, amines and inorganic compounds, concomitantly with the reduction of molecular dioxygen to water. This family of enzymes can be broadly divided into two functional classes: metalloxidases and laccases. Several prokaryotic metalloxidases have been described in the last decade showing a robust activity towards metals, such as Cu(I), Fe(II) or Mn(II) and have been implicated in the metal metabolism of the corresponding microorganisms. Many laccases, with a superior efficiency for oxidation of organic compounds when compared with metals, have also been identified and characterized from prokaryotes, playing roles that more closely conform to those of intermediary metabolism. This review aims to present an update of current knowledge on prokaryotic multicopper oxidases, with a special emphasis on laccases, anticipating their enormous potential for industrial and environmental applications.
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Affiliation(s)
- Lígia O Martins
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2781-901, Oeiras, Portugal,
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12
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Direct electron transfer of Trametes hirsuta laccase adsorbed at unmodified nanoporous gold electrodes. Bioelectrochemistry 2013; 91:15-20. [DOI: 10.1016/j.bioelechem.2012.11.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2012] [Revised: 11/19/2012] [Accepted: 11/26/2012] [Indexed: 11/20/2022]
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13
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Abdellaoui S, Noiriel A, Henkens R, Bonaventura C, Blum LJ, Doumèche B. A 96-well electrochemical method for the screening of enzymatic activities. Anal Chem 2013; 85:3690-7. [PMID: 23461701 DOI: 10.1021/ac303777r] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The rapid electrochemical screening of enzyme activities in bioelectronics is still a challenging issue. In order to solve this problem, we propose to use a 96-well electrochemical assay. This system is composed of 96 screen-printed electrodes on a printed circuit board adapted from a commercial system (carbon is used as the working electrode and silver chloride as the counter/reference electrode). The associated device allows for the measurements on the 96 electrodes to be performed within a few seconds. In this work, we demonstrate the validity of the screening method with the commercial laccase from the fungus Trametes versicolor. The signal-to-noise ratio (S/N) is found to be the best way to analyze the electrochemical signals. The S/N follows a saturation-like mechanism with a dynamic linear range of two decades ranging from 0.5 to 75 ng of laccase (corresponding to enzymatic activities from 62 × 10(-6) to 9.37 × 10(-3) μmol min(-1)) and a sensitivity of 3027 μg(-1) at +100 mV versus Ag/AgCl. Laccase inhibitors (azide and fluoride anions), pH optima, and interfering molecules could also be identified within a few minutes.
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Affiliation(s)
- Sofiène Abdellaoui
- GEMBAS (Génie Enzymatique, Membranes Biomimétiques et Assemblages Supramoléculaires), ICBMS UMR 5246, Université Lyon 1, CNRS, INSA Lyon, Villeurbanne, France
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14
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Suraniti E, Tsujimura S, Durand F, Mano N. Thermophilic biocathode with bilirubin oxidase from Bacillus pumilus. Electrochem commun 2013. [DOI: 10.1016/j.elecom.2012.10.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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15
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Beneyton T, Wijaya IPM, Salem CB, Griffiths AD, Taly V. Membraneless glucose/O2 microfluidic biofuel cells using covalently bound enzymes. Chem Commun (Camb) 2013; 49:1094-6. [DOI: 10.1039/c2cc37906f] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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16
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17
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Brissos V, Chen Z, Martins LO. The kinetic role of carboxylate residues in the proximity of the trinuclear centre in the O2 reactivity of CotA-laccase. Dalton Trans 2012; 41:6247-55. [PMID: 22481612 DOI: 10.1039/c2dt12067d] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Multicopper oxidases catalyze the four-electron reduction of dioxygen to water without the release of any reactive oxygen intermediate species. The role of carboxylate residue Asp116 located at the exit channel for water molecules of CotA-laccase has been investigated by site-saturation mutagenesis. A total of 300 clones was picked and screened for activity. Five variant enzymes, D116E, D116A, D116N, D116T and D116L, were selected for further characterisation. Spectroscopic analysis revealed only small perturbations in the geometry of the catalytic Cu sites of variants. However, a severe drop in turnover numbers (k(cat)) and downshifts by approximately 1-2 units of the optimal pH were observed for the oxidation of substrates, as compared with the wild type. The kinetics of formation and decay of peroxide intermediate (PI) was studied in type 1 depleted (T1D) CotA-laccase and in T1D-D116 or T1D-E498 mutants, previously shown to be involved in the mechanism of dioxygen reduction. It is noteworthy that CotA shows 10 times lower rates of PI formation and 10(3) higher PI decay rates as compared with other studied multicopper oxidases. The generation of PI is pH independent and mostly unaffected by the D116 or E498 mutations. In contrast, the decay of PI is markedly compromised by the replacement of D116 or E498 with non-carboxylate residues. The E498 residue appears to be the main protonable species for acceleration of PI decay at low pH. The D116 residue seems to be essential in the modulation of E498 protonation and in assisting protons to hydroxyl groups bound to the T2 Cu.
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Affiliation(s)
- Vânia Brissos
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. Da República, 2781-901 Oeiras, Portugal
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