| 1. |
- Ignatenko, O. V., et al.
(författare)
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Electrochemistry of chemically trapped dimeric and monomeric recombinant horseradish peroxidase
- 2013
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Ingår i: Advances in Biosensors and Bioelectronics. - : Science and Engineering Publishing Company. - 2326-473X. ; 2:3, s. 25-34
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Tidskriftsartikel (refereegranskat)abstract
- Native horseradish peroxidase (nHRP) exists in the aggregated form in concentrated water solutions as shown by dynamic light scattering (DLS). This is in contrast to recombinant horseradish peroxidase (recHRP) which mainly exists as a dimer. The native enzyme aggregates could be broken into the particles of nm-size only under the conditions of high ionic strength (0.5-1 M NaCl). Chemical cross-linking of recHRP with glutaraldehyde in water solutions yields 40% of the dimer. The chemically trapped dimeric and monomeric forms of recHRP were separated by gel-filtration, their substrate specificity towards a number of organic substrates compared. Parameters of direct and mediated electron transfer on graphite electrodes catalyzed by both preparations were analyzed. The difference in behavior of the monomeric and dimeric enzyme forms observed in electrochemical experiments was interpreted as a result of a “double” coverage of the electrode surface with the molecules of cross-linked dimeric enzyme, in contrast to both modified monomeric and original, unmodified recHRP providing “monolayer” coverage. In addition to the stabilization effects achieved due to enzyme surface modification with glutaraldehyde, the “double” coverage doubles the enzyme activity per surface unit.
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| 2. |
- Castillo, John, et al.
(författare)
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Direct electrochemistry and biolelectrocatalysis of H2O2 reduction of recombinant tobacco peroxidase on graphite. Effect of peroxidase single-point mutation on Ca2+-modulated catalytic activity
- 2006
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 588:1, s. 112-121
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Tidskriftsartikel (refereegranskat)abstract
- Direct electron transfer (DET) reactions and bio(electro)catalytic reduction of H2O2 catalysed by native and recombinant forms of tobacco peroxidase (nTOP and rTOP) were studied in homogeneous-phase catalysis and when TOPs were adsorbed on graphite electrodes. Non-glycosylated wild type and Glu141 -> Phe mutant forms of rTOP were produced using an Escherichia coli expression system. Mutation was introduced to explore the mechanisms for modulation of the catalytic activity of TOP by Ca2+ ions. At the pH optimum of 5.0, direct electrochemical Fe3+/2+ transformation of the peroxidase heme was characterised by potentials of -208 mV (nTOP) and -239 mV vs. Ag vertical bar AgCl (rTOP), and 0.9 +/- 0.1 and 1.1 +/- 0.4 pmoles of adsorbed nTOP and rTOP, correspondingly, were in DET contact with graphite. Kinetic analysis of amperometric (at +50 mV) data on H2O2 reduction at TOP-modified electrodes, placed in a wall-jet flow-through electrochemical cell, yielded 82% (nTOP) and 88% (rTOP) of adsorbed TOP molecules active in the DET reaction. The efficiency of DET (and bioelectrocatalysis) increased 3.5-fold when changing from glycosylated nTOP to rTOP. The Glu141 Phe mutation in the heme-binding pocket of rTOP enabled to achieve a Ca2+-tolerance of TOP in the reaction with H2O2, which is characteristic of other plant peroxidases, and to a large extent in heterogeneous DET and reaction with a second substrate catechol. The results promote further applications of TOP for biosensor- and solid-phase biocatalysts development. (c) 2005 Elsevier B.V. All rights reserved.
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| 3. |
- Dima, Danai, et al.
(författare)
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Subcortical volumes across the lifespan : Data from 18,605 healthy individuals aged 3-90 years.
- 2022
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Ingår i: Human Brain Mapping. - : Wiley. - 1065-9471 .- 1097-0193. ; 43:1, s. 452-469
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Tidskriftsartikel (refereegranskat)abstract
- Age has a major effect on brain volume. However, the normative studies available are constrained by small sample sizes, restricted age coverage and significant methodological variability. These limitations introduce inconsistencies and may obscure or distort the lifespan trajectories of brain morphometry. In response, we capitalized on the resources of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) Consortium to examine age-related trajectories inferred from cross-sectional measures of the ventricles, the basal ganglia (caudate, putamen, pallidum, and nucleus accumbens), the thalamus, hippocampus and amygdala using magnetic resonance imaging data obtained from 18,605 individuals aged 3-90 years. All subcortical structure volumes were at their maximum value early in life. The volume of the basal ganglia showed a monotonic negative association with age thereafter; there was no significant association between age and the volumes of the thalamus, amygdala and the hippocampus (with some degree of decline in thalamus) until the sixth decade of life after which they also showed a steep negative association with age. The lateral ventricles showed continuous enlargement throughout the lifespan. Age was positively associated with inter-individual variability in the hippocampus and amygdala and the lateral ventricles. These results were robust to potential confounders and could be used to examine the functional significance of deviations from typical age-related morphometric patterns.
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| 4. |
- Ferapontova, Elena, et al.
(författare)
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Direct electrochemistry of recombinant tobacco peroxidase on gold
- 2005
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Ingår i: Electrochemistry Communications. - : Elsevier BV. - 1388-2481. ; 7:12, s. 1291-1297
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Tidskriftsartikel (refereegranskat)abstract
- Direct electron transfer (DET) reactions of recombinant tobacco peroxidase (rTOP), namely direct electroreduction of Compound I/ Compound II and heme Fe3+/2+ conversion, were studied on gold electrodes. rTOP of wild type, non-glycosylated, was produced using, an Escherichia coli expression system. At pH 5.0, the redox potential for direct electrochemical transformation of the Fe3+/2+ of the peroxidase heme was -143 mV vs. Ag vertical bar AgCl, and 0.26 +/- 0.07 pmol of the adsorbed rTOP were in DET contact with the gold electrode. The total amount of the adsorbed rTOP estimated from QCM data was 53 +/- 5 pmol/cm(2) or 1.67 pmol when referred to the surface area of the electrodes used for electrochemical measurements. Of 1.67 pmol of adsorbed rTOP, only 0.76 pmol were catalytically active. DET between Au and the enzyme was also studied in the reaction of the bioelectrocatalytic reduction of H2O2 by cyclic voltammetry and amperometric detection of H2O2 at +50 mV with rTOP-modified Au electrodes placed in a wall-jet flow-through electrochemical cell. Maximal bioelectrocatalytic current response of the rTOP-modified gold electrodes to H2O2 was observed at pH 5.0 and stemmed from its bioelectrocatalytic reduction based on DET between Au and the active site of rTOP. Kinetic analysis of the DET reactions gave 52% of the adsorbed rTOP molecules active in DET reactions (0.4 pmol of adsorbed catalytically active rTOP, correspondingly), which correlated well with the non-catalytic-voltammetry data. DET was characterised by a heterogeneous ET rate constant of 13.2 s(-1), if one takes into account the QCM data, and 19.6 s(-1), if the amount of rTOP estimated from the data on DET transformation of Fe3+/2+ couple of rTOP is considered. The sensitivity for H2O2 obtained for the rTOP-modified Au electrodes was 0.7 +/- 0.1 A M-1 cm(-2). These are the first ever-reported data on DET reactions of anionic plant peroxidases on bare gold electrodes. (c) 2005 Elsevier B.V. All rights reserved.
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| 5. |
- Frangou, Sophia, et al.
(författare)
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Cortical thickness across the lifespan : Data from 17,075 healthy individuals aged 3-90 years
- 2022
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Ingår i: Human Brain Mapping. - : John Wiley & Sons. - 1065-9471 .- 1097-0193. ; 43:1, s. 431-451
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Tidskriftsartikel (refereegranskat)abstract
- Delineating the association of age and cortical thickness in healthy individuals is critical given the association of cortical thickness with cognition and behavior. Previous research has shown that robust estimates of the association between age and brain morphometry require large-scale studies. In response, we used cross-sectional data from 17,075 individuals aged 3-90 years from the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) Consortium to infer age-related changes in cortical thickness. We used fractional polynomial (FP) regression to quantify the association between age and cortical thickness, and we computed normalized growth centiles using the parametric Lambda, Mu, and Sigma method. Interindividual variability was estimated using meta-analysis and one-way analysis of variance. For most regions, their highest cortical thickness value was observed in childhood. Age and cortical thickness showed a negative association; the slope was steeper up to the third decade of life and more gradual thereafter; notable exceptions to this general pattern were entorhinal, temporopolar, and anterior cingulate cortices. Interindividual variability was largest in temporal and frontal regions across the lifespan. Age and its FP combinations explained up to 59% variance in cortical thickness. These results may form the basis of further investigation on normative deviation in cortical thickness and its significance for behavioral and cognitive outcomes.
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