scholarly journals Reduction of ferric haemoproteins by tetrahydropterins: a kinetic study

2005 ◽  
Vol 392 (3) ◽  
pp. 583-587 ◽  
Author(s):  
Chantal Capeillere-Blandin ◽  
Delphine Mathieu ◽  
Daniel Mansuy
Keyword(s):  
Electron Transfer ◽  
Cytochrome C ◽  
Cytochrome B5 ◽  
Reduction Rate ◽  
Cation Radical ◽  
Order Reduction ◽  
Reduction Potentials ◽  
Electron Reduction ◽  
The One

We previously showed that one-electron transfer from tetrahydropterins to iron porphyrins is a very general reaction, with formation of an intermediate cation radical similar to the one detected in NO synthase. As a model reaction, the rates of reduction of eight haemoproteins by diMePH4 (6,7-dimethyltetrahydropterin) have been studied and correlated with their one-electron reduction potentials, Em (FeIII/FeII). On the basis of kinetic data analyses, a bimolecular collisional mechanism is proposed for the electron transfer from diMePH4 to ferrihaemoproteins. Haemoproteins with reduction potentials below −160 mV were shown not to be reduced by diMePH4 to the corresponding ferrohaemoproteins. For haemoproteins with reduction potentials more positive than −160 mV, such as chloroperoxidase, cytochrome b5, methaemoglobin and cytochrome c, there was a good correlation between the second-order reduction rate constant and the redox potential, Em (FeIII/FeII):The rate of reduction of cytochrome c by BH4 [(6R)-5,6,7,8-tetrahydrobiopterin] was determined to be similar to that of the reduction of cytochrome c by diMePH4. These results confirm the role of tetrahydropterins as one-electron donors to FeIII porphyrins.

scholarly journals Theoretical Study on the Photo-Oxidation and Photoreduction of an Azetidine Derivative as a Model of DNA Repair

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2911
Author(s):  
Miriam Navarrete-Miguel ◽  
Antonio Francés-Monerris ◽  
Miguel A. Miranda ◽  
Virginie Lhiaubet-Vallet ◽  
Daniel Roca-Sanjuán
Keyword(s):  
Electron Transfer ◽  
Energy Barrier ◽  
Ring Opening ◽  
Dna Lesions ◽  
Barrier Heights ◽  
Dna Lesion ◽  
Electron Reduction ◽  
The Stability ◽  
Electron Transfer Processes

Photocycloreversion plays a central role in the study of the repair of DNA lesions, reverting them into the original pyrimidine nucleobases. Particularly, among the proposed mechanisms for the repair of DNA (6-4) photoproducts by photolyases, it has been suggested that it takes place through an intermediate characterized by a four-membered heterocyclic oxetane or azetidine ring, whose opening requires the reduction of the fused nucleobases. The specific role of this electron transfer step and its impact on the ring opening energetics remain to be understood. These processes are studied herein by means of quantum-chemical calculations on the two azetidine stereoisomers obtained from photocycloaddition between 6-azauracil and cyclohexene. First, we analyze the efficiency of the electron-transfer processes by computing the redox properties of the azetidine isomers as well as those of a series of aromatic photosensitizers acting as photoreductants and photo-oxidants. We find certain stereodifferentiation favoring oxidation of the cis-isomer, in agreement with previous experimental data. Second, we determine the reaction profiles of the ring-opening mechanism of the cationic, neutral, and anionic systems and assess their feasibility based on their energy barrier heights and the stability of the reactants and products. Results show that oxidation largely decreases the ring-opening energy barrier for both stereoisomers, even though the process is forecast as too slow to be competitive. Conversely, one-electron reduction dramatically facilitates the ring opening of the azetidine heterocycle. Considering the overall quantum-chemistry findings, N,N-dimethylaniline is proposed as an efficient photosensitizer to trigger the photoinduced cycloreversion of the DNA lesion model.

scholarly journals One-Electron Reduction Potentials: Calibration of Theoretical Protocols for Morita–Baylis–Hillman Nitroaromatic Compounds in Aprotic Media

Molecules ◽  
2018 ◽  
Vol 23 (9) ◽  
pp. 2129 ◽  
Author(s):  
Amauri Francisco da Silva ◽  
Antonio João da Silva Filho ◽  
Mário Vasconcellos ◽  
Otávio Luís de Santana
Keyword(s):  
Cyclic Voltammetry ◽  
Biological Activity ◽  
Chemical Structure ◽  
Reduction Potential ◽  
Chemical Reactivity ◽  
Nitroaromatic Compounds ◽  
Reduction Potentials ◽  
Electron Reduction ◽  
The One ◽  
Antileishmanial Activities

Nitroaromatic compounds—adducts of Morita–Baylis–Hillman (MBHA) reaction—have been applied in the treatment of malaria, leishmaniasis, and Chagas disease. The biological activity of these compounds is directly related to chemical reactivity in the environment, chemical structure of the compound, and reduction of the nitro group. Because of the last aspect, electrochemical methods are used to simulate the pharmacological activity of nitroaromatic compounds. In particular, previous studies have shown a correlation between the one-electron reduction potentials in aprotic medium (estimated by cyclic voltammetry) and antileishmanial activities (measured by the IC50) for a series of twelve MBHA. In the present work, two different computational protocols were calibrated to simulate the reduction potentials for this series of molecules with the aim of supporting the molecular modeling of new pharmacological compounds from the prediction of their reduction potentials. The results showed that it was possible to predict the experimental reduction potential for the calibration set with mean absolute errors of less than 25 mV (about 0.6 kcal·mol−1).

Role of methionine 230 in intramolecular electron transfer between the oxyferryl heme and tryptophan 191 in cytochrome c peroxidase compound II

Biochemistry ◽  
1994 ◽  
Vol 33 (29) ◽  
pp. 8678-8685 ◽  
Author(s):  
Rui-Qin Liu ◽  
Mark A. Miller ◽  
Gye Won Han ◽  
Seung Hahm ◽  
Lois Geren ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Cytochrome C ◽  
Cytochrome C Peroxidase ◽  
Intramolecular Electron Transfer ◽  
Compound Ii

Effects of base pairing on the one-electron reduction rate of cytosine

2003 ◽  
pp. 2840 ◽  
Author(s):  
Kiyohiko Kawai ◽  
Aya Yokoohji ◽  
Sachiko Tojo ◽  
Tetsuro Majima
Keyword(s):  
Reduction Rate ◽  
Base Pairing ◽  
Electron Reduction ◽  
The One

The role of distal tryptophan in the bifunctional activity of catalase-peroxidases

2001 ◽  
Vol 29 (2) ◽  
pp. 99-105 ◽  
Author(s):  
G. Regelsberger ◽  
C. Jakopitsch ◽  
P. G. Furtmüller ◽  
F. Rueker ◽  
J. Switala ◽  
...  
Keyword(s):  
Catalase Activity ◽  
Intermediate Compound ◽  
Stopped Flow ◽  
Wild Type ◽  
Compound I ◽  
Wild Type Enzyme ◽  
Catalase Peroxidase ◽  
Electron Reduction ◽  
The One

Catalase-peroxidases are bifunctional peroxidases exhibiting an overwhelming catalase activity and a substantial peroxidase activity. Here we present a kinetic study of the formation and reduction of the key intermediate compound I by probing the role of the conserved tryptophan at the distal haem cavity site. Two wild-type proteins and three mutants of Synechocystis catalase-peroxidase (W122A and W122F) and Escherichia coli catalase-peroxidase (W105F) have been investigated by steady-state and stopped-flow spectroscopy. W122F and W122A completely lost their catalase activity whereas in W105F the catalase activity was reduced by a factor of about 5000. However, the mutations did not influence both formation of compound I and its reduction by peroxidase substrates. It was demonstrated unequivocally that the rate of compound I reduction by pyrogallol or o-dianisidine sometimes even exceeded that of the wild-type enzyme. This study demonstrates that the indole ring of distal Trp in catalase-peroxidases is essential for the two-electron reduction of compound I by hydrogen peroxide but not for compound I formation or for peroxidase reactivity (i.e. the one-electron reduction of compound I).

The structural and functional role of lysine residues in the binding domain of cytochrome c in the electron transfer to cytochrome c oxidase

1999 ◽  
Vol 261 (2) ◽  
pp. 379-391 ◽  
Author(s):  
Susanne Dopner ◽  
Peter Hildebrandt ◽  
Federico I. Rosell ◽  
A. Grant Mauk ◽  
Matthias von Walter ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Functional Role ◽  
Binding Domain ◽  
Lysine Residues
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