The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Andrew C Lawler - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of Heme Peripheral Group Interactions in Extremely Low-Dielectric Constant Media and Their Contributions to the Heme Reduction Potential.
2014Co-Authors: Jose F. Cerda, Mary C. Malloy, Brady O. Werkheiser, Alaina T. Stockhausen, Michael F Gallagher, Andrew C LawlerAbstract:In this study, we measured the contributions of the ionization of the heme Propionates to the reduction potentials of heme b and heme a (bis)N-methylimidazole complexes in various low-dielectric constant conditions. Additionally, we measured the effects of H-bond to the heme a formyl group on the reduction potential of the heme. The performed electrochemical measurements show that ionization of the heme Propionates lead to the largest redox change in dichloromethane with no electrolyte. The measured reduction potential changes for heme b and heme a were −55 and −47 mV (±10 mV) per ionized propionate, respectively. For heme a, the study demonstrates how the dielectric constant of the medium is important in the magnification of the ΔpKa upon redox-linked ionization of the heme Propionates and their roles in the proton pump of cytochrome c oxidase
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Evaluation of heme peripheral group interactions in extremely low-dielectric constant media and their contributions to the heme reduction potential.
Inorganic chemistry, 2013Co-Authors: Jose F. Cerda, Mary C. Malloy, Brady O. Werkheiser, Alaina T. Stockhausen, Michael F Gallagher, Andrew C LawlerAbstract:In this study, we measured the contributions of the ionization of the heme Propionates to the reduction potentials of heme b and heme a (bis)N-methylimidazole complexes in various low-dielectric constant conditions. Additionally, we measured the effects of H-bond to the heme a formyl group on the reduction potential of the heme. The performed electrochemical measurements show that ionization of the heme Propionates lead to the largest redox change in dichloromethane with no electrolyte. The measured reduction potential changes for heme b and heme a were -55 and -47 mV (±10 mV) per ionized propionate, respectively. For heme a, the study demonstrates how the dielectric constant of the medium is important in the magnification of the ΔpKa upon redox-linked ionization of the heme Propionates and their roles in the proton pump of cytochrome c oxidase.
Ralf Conrad - One of the best experts on this subject based on the ideXlab platform.
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Turnover of propionate in methanogenic paddy soil
FEMS Microbiology Ecology, 2006Co-Authors: Nailia I Krylova, Peter H. Janssen, Ralf ConradAbstract:Samples from planted Italian paddy soil exhibited most probable numbers (MPN) of about 107 anaerobic propionate utilizers. In anoxic soil slurries that were either unamended or amended with rice straw production of CH4 was measured together with concentrations of H2, acetate and propionate. After a lag phase, during which ferric iron was depleted, CH4 was produced at a constant rate which was slightly higher in the straw-amended than in the unamended soil. Propionate concentrations were relatively low at about 5–15 μM. However, in the straw-amended soil propionate transiently accumulated to about 35 μM just after onset of methanogenesis. During the period of propionate accumulation H2 partial pressures were elevated and the Gibbs free energy (ΔG) of propionate consumption to acetate, bicarbonate and H2 was endergonic or higher than −3 kJ mol−1 propionate. Propionate concentrations decreased again when the ΔG decreased to more negative values. In unamended paddy soil, propionate did not accumulate transiently and ΔG was always
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Thermodynamics of propionate degradation in methanogenic paddy soil
FEMS Microbiology Ecology, 1998Co-Authors: Nailia I Krylova, Ralf ConradAbstract:Abstract Propionate is syntrophically degraded in methanogenic paddy soil via a randomizing pathway. To study the thermodynamic conditions of this syntrophy, propionate degradation was measured in the presence of different H 2 partial pressures (1–20 000 Pa) using methanogenic soil slurries taken from planted Italian paddy soil. The logarithmic decrease of [1- 14 C]propionate or [2- 14 C]propionate was measured during an incubation period of about 2–3 h to determine degradation rate constants ( k ). The change of the H 2 partial pressure was measured during the same period. Values of k decreased with increasing H 2 partial pressures (averaged over the incubation period). However, k was still relatively high, although the Gibbs free energy (ΔG) of syntrophic propionate conversion to acetate, bicarbonate and H 2 was already strongly endergonic reaching ΔG values of +60 kJ mol −1 propionate. Assuming propionate conversion to acetate plus formate resulted in the same or even higher ΔG values indicating that this degradation pathway was not realistic. We therefore assume that propionate was degraded within microbial aggregates in which syntrophic propionate degraders were shielded from thermodynamically unfavorable H 2 by methanogenic bacteria consuming H 2 . Gibbs free energies for H 2 formation from propionate correlated negatively with the ΔG values for H 2 conversion to CH 4 , but the latter values were generally −1 H 2 so that methanogenesis from H 2 was always possible. Addition of sulfate did not result in a significant decrease of the ΔG values for H 2 formation from propionate demonstrating that H 2 consumption by sulfate reducers was not relevant during the short incubation period. Nevertheless, propionate degradation was less strongly inhibited by H 2 when sulfate was present indicating that propionate was then mainly degraded by sulfate reduction rather than by syntrophy. The major degradation product of [2- 14 C]propionate was 14 C-acetate (followed by 14 CO 2 and 14 CH 4 ) showing that the sulfate reducers oxidized propionate primarily to acetate, bicarbonate and H 2 . As a conceptual model we therefore speculate that propionate was degraded within methanogenic bacterial aggregates both in the presence and the absence of sulfate and that propionate degraders operated either as sulfate reducers or as H 2 -producing syntrophs.
Inez M Weidinger - One of the best experts on this subject based on the ideXlab platform.
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redox induced protonation of heme Propionates in cytochrome c oxidase insights from surface enhanced resonance raman spectroscopy and qm mm calculations
Biochimica et Biophysica Acta, 2017Co-Authors: Murat Sezer, Anna Lena Woelke, Ernstwalter Knapp, Ramona Schlesinger, Maria Andrea Mroginski, Inez M WeidingerAbstract:Understanding the coupling between heme reduction and proton translocation in cytochrome c oxidase (CcO) is still an open problem. The propionic acids of heme a3 have been proposed to act as a proton loading site (PLS) in the proton pumping pathway, yet this proposal could not be verified by experimental data so far. We have set up an experiment where the redox states of the two hemes in CcO can be controlled via external electrical potential. Surface enhanced resonance Raman (SERR) spectroscopy was applied to simultaneously monitor the redox state of the hemes and the protonation state of the heme Propionates. Simulated spectra based on QM/MM calculations were used to assign the resonant enhanced CH2 twisting modes of the Propionates to the protonation state of the individual heme a and heme a3 Propionates respectively. The comparison between calculated and measured H2OD2O difference spectra allowed a sound band assignment. In the fully reduced enzyme at least three of the four heme Propionates were found to be protonated whereas in the presence of a reduced heme a and an oxidized heme a3 only protonation of one heme a3 Propionates was observed. Our data supports the postulated scenario where the heme a3 Propionates are involved in the proton pathway.
Jose F. Cerda - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of Heme Peripheral Group Interactions in Extremely Low-Dielectric Constant Media and Their Contributions to the Heme Reduction Potential.
2014Co-Authors: Jose F. Cerda, Mary C. Malloy, Brady O. Werkheiser, Alaina T. Stockhausen, Michael F Gallagher, Andrew C LawlerAbstract:In this study, we measured the contributions of the ionization of the heme Propionates to the reduction potentials of heme b and heme a (bis)N-methylimidazole complexes in various low-dielectric constant conditions. Additionally, we measured the effects of H-bond to the heme a formyl group on the reduction potential of the heme. The performed electrochemical measurements show that ionization of the heme Propionates lead to the largest redox change in dichloromethane with no electrolyte. The measured reduction potential changes for heme b and heme a were −55 and −47 mV (±10 mV) per ionized propionate, respectively. For heme a, the study demonstrates how the dielectric constant of the medium is important in the magnification of the ΔpKa upon redox-linked ionization of the heme Propionates and their roles in the proton pump of cytochrome c oxidase
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Evaluation of heme peripheral group interactions in extremely low-dielectric constant media and their contributions to the heme reduction potential.
Inorganic chemistry, 2013Co-Authors: Jose F. Cerda, Mary C. Malloy, Brady O. Werkheiser, Alaina T. Stockhausen, Michael F Gallagher, Andrew C LawlerAbstract:In this study, we measured the contributions of the ionization of the heme Propionates to the reduction potentials of heme b and heme a (bis)N-methylimidazole complexes in various low-dielectric constant conditions. Additionally, we measured the effects of H-bond to the heme a formyl group on the reduction potential of the heme. The performed electrochemical measurements show that ionization of the heme Propionates lead to the largest redox change in dichloromethane with no electrolyte. The measured reduction potential changes for heme b and heme a were -55 and -47 mV (±10 mV) per ionized propionate, respectively. For heme a, the study demonstrates how the dielectric constant of the medium is important in the magnification of the ΔpKa upon redox-linked ionization of the heme Propionates and their roles in the proton pump of cytochrome c oxidase.
Nailia I Krylova - One of the best experts on this subject based on the ideXlab platform.
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Turnover of propionate in methanogenic paddy soil
FEMS Microbiology Ecology, 2006Co-Authors: Nailia I Krylova, Peter H. Janssen, Ralf ConradAbstract:Samples from planted Italian paddy soil exhibited most probable numbers (MPN) of about 107 anaerobic propionate utilizers. In anoxic soil slurries that were either unamended or amended with rice straw production of CH4 was measured together with concentrations of H2, acetate and propionate. After a lag phase, during which ferric iron was depleted, CH4 was produced at a constant rate which was slightly higher in the straw-amended than in the unamended soil. Propionate concentrations were relatively low at about 5–15 μM. However, in the straw-amended soil propionate transiently accumulated to about 35 μM just after onset of methanogenesis. During the period of propionate accumulation H2 partial pressures were elevated and the Gibbs free energy (ΔG) of propionate consumption to acetate, bicarbonate and H2 was endergonic or higher than −3 kJ mol−1 propionate. Propionate concentrations decreased again when the ΔG decreased to more negative values. In unamended paddy soil, propionate did not accumulate transiently and ΔG was always
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Thermodynamics of propionate degradation in methanogenic paddy soil
FEMS Microbiology Ecology, 1998Co-Authors: Nailia I Krylova, Ralf ConradAbstract:Abstract Propionate is syntrophically degraded in methanogenic paddy soil via a randomizing pathway. To study the thermodynamic conditions of this syntrophy, propionate degradation was measured in the presence of different H 2 partial pressures (1–20 000 Pa) using methanogenic soil slurries taken from planted Italian paddy soil. The logarithmic decrease of [1- 14 C]propionate or [2- 14 C]propionate was measured during an incubation period of about 2–3 h to determine degradation rate constants ( k ). The change of the H 2 partial pressure was measured during the same period. Values of k decreased with increasing H 2 partial pressures (averaged over the incubation period). However, k was still relatively high, although the Gibbs free energy (ΔG) of syntrophic propionate conversion to acetate, bicarbonate and H 2 was already strongly endergonic reaching ΔG values of +60 kJ mol −1 propionate. Assuming propionate conversion to acetate plus formate resulted in the same or even higher ΔG values indicating that this degradation pathway was not realistic. We therefore assume that propionate was degraded within microbial aggregates in which syntrophic propionate degraders were shielded from thermodynamically unfavorable H 2 by methanogenic bacteria consuming H 2 . Gibbs free energies for H 2 formation from propionate correlated negatively with the ΔG values for H 2 conversion to CH 4 , but the latter values were generally −1 H 2 so that methanogenesis from H 2 was always possible. Addition of sulfate did not result in a significant decrease of the ΔG values for H 2 formation from propionate demonstrating that H 2 consumption by sulfate reducers was not relevant during the short incubation period. Nevertheless, propionate degradation was less strongly inhibited by H 2 when sulfate was present indicating that propionate was then mainly degraded by sulfate reduction rather than by syntrophy. The major degradation product of [2- 14 C]propionate was 14 C-acetate (followed by 14 CO 2 and 14 CH 4 ) showing that the sulfate reducers oxidized propionate primarily to acetate, bicarbonate and H 2 . As a conceptual model we therefore speculate that propionate was degraded within methanogenic bacterial aggregates both in the presence and the absence of sulfate and that propionate degraders operated either as sulfate reducers or as H 2 -producing syntrophs.
