Ferric heme as a CO/NO sensor in the nuclear receptor Rev-Erbß by coupling gas binding to electron transfer

Rev-Erbβ is a nuclear receptor that couples circadian rhythm, metabolism, and inflammation. Heme binding to the protein modulates its function as a repressor, its stability, its ability to bind other proteins, and its activity in gas sensing. Rev-Erbβ binds Fe3+-heme more tightly than Fe2+-heme, suggesting its activities may be regulated by the heme redox state. Yet, this critical role of heme redox chemistry in defining the protein’s resting state and function is unknown. We demonstrate by electrochemical and whole-cell electron paramagnetic resonance experiments that Rev-Erbβ exists in the Fe3+ form within the cell allowing the protein to be heme replete even at low concentrations of labile heme in the nucleus. However, being in the Fe3+ redox state contradicts Rev-Erb’s known function as a gas sensor, which dogma asserts must be Fe2+. This paper explains why the resting Fe3+ state is congruent both with heme binding and cellular gas sensing. We show that the binding of CO/NO elicits a striking increase in the redox potential of the Fe3+/Fe2+ couple, characteristic of an EC mechanism in which the unfavorable Electrochemical reduction of heme is coupled to the highly favorable Chemical reaction of gas binding, making the reduction spontaneous. Thus, Fe3+-Rev-Erbβ remains heme-loaded, crucial for its repressor activity, and undergoes reduction when diatomic gases are present. This work has broad implications for proteins in which ligand-triggered redox changes cause conformational changes influencing its function or interprotein interactions (e.g., between NCoR1 and Rev-Erbβ). This study opens up the possibility of CO/NO-mediated regulation of the circadian rhythm through redox changes in Rev-Erbβ.

Voltammetric Generation and Kinetic Stability of Nitro Anion Radical from Nitrofurazone in Ionic Liquids

The nitrofurazone (NF) electrochemical reduction has been studied by cyclic voltammetry (CV) and square wave voltammetry (SWV) in non-aqueous medium using three different ionic liquids (IL): BMImTf2N, BMImBF4 and BMMImTf2N, having a carbon fiber microelectrode as working electrode. In all of them, two reversible cathodic peaks were recorded for NF. Under higher frequency values, only one reversible cathodic peak was registered. The systems reversibility could also be observed by CV, since a reversible redox couple was registered for this reduction. The systems reversibility with product and reagent adsorptions on the electrode surface was confirmed and the electrons number involved in this reduction indicated the nitro-anion radical formation followed by its respective dianion. For the first reduction, the EC mechanism (an electrochemical step followed by a chemical one) was considered for the systems in aprotic medium, in which there was a probable second-order chemical reaction after the charge transfer process, being the kinetic constants calculated following the Olmstead and Nicholson model.

Ferric Heme as a CO/NO Sensor in the Nuclear Receptor Reverbβ by Coupling Gas binding to Electron Transfer

Rev-Erbβ is a nuclear receptor that couples circadian rhythm, metabolism, and inflammation.1-7 Heme binding to the protein modulates its function as a repressor, its stability, its ability to bind other proteins, and its activity in gas sensing.8-11 Rev-Erbβ binds Fe3+-heme tighter than Fe2+-heme, suggesting its activities may be regulated by the heme redox state.9 Yet, this critical role of heme redox chemistry in defining the protein’s resting state and function is unknown. We demonstrate by electrochemical and whole-cell electron paramagnetic resonance experiments that Rev-Erbβ exists in the Fe3+ form within the cell essentially allowing the protein to be heme-replete even at low concentrations of labile heme in the nucleus. However, being in the Fe3+ redox state contradicts Rev-Erb’s known function as a gas sensor, which dogma asserts must be a Fe2+ protein This paper explains why the resting Fe3+-state is congruent both with heme-binding and cellular gas sensing. We show that the binding of CO/NO elicits a striking increase in the redox potential of the Fe3+/Fe2+ couple, characteristic of an EC mechanism in which the unfavorable Electrochemical reduction of heme is coupled to the highly favorable Chemical reaction of gas binding, making the reduction spontaneous. Thus, Fe3+-Rev-Erbβ remains heme-loaded, crucial for its repressor activity, and only undergoes reduction when diatomic gases are present. This work has broad implications for hemoproteins where ligand-triggered redox changes cause conformational changes influencing protein’s function or inter-protein interactions, like NCoR1 for Rev-Erbβ. This study opens up the possibility of CO/NO-mediated regulation of the circadian rhythm through redox changes in Rev-Erbβ.

Study of Electron Transfer Reactions Associated with Benzyl Viologen-β-Cyclodextrin Complexation in Buffer Solution of pH 7: Equilibrium and Kinetic Aspects

In this study, complex formation of benzyl viologen dication (BzV2+) with β-cyclodextrin (β-CD), in its different oxidation states, had been studied in buffer solution of pH 7, through cyclic voltammetry. In buffer solution of pH 7, extensive deposition of benzyl viologen neutral (BzVº) has been found. Further to that first redox process of BzV2+ was found reversible in buffer solution of pH 7. Benzyl viologen mono-cation (BzV+•) was found to interact with β-CD reversibly according to EC mechanism. Equilibrium constant of BzV+•-nβ-CD complex in buffer solution of pH 7, has been calculated as 5.49 M-n. The value of n was found to be 0.2. The bimolecular rate constant for the complex formation of BzV+• with β-CD was found to be 6.44 M-ns− in buffer solution of pH 7. This study is based upon an electrochemical approach to obtain the bonding equilibrium constant, the rate constants of formation and the association numbers of the complex formed between reduced forms of viologen and β-CD. This study explore the electron transfer reaction mechanism of benzyl viologen with β-CD to extend their applications at neutral pH.

Diffusional Electrochemical Catalytic (EC’) Mechanism Featuring Chemical Reversibility of Regenerative Reaction-Theoretical Analysis in Cyclic Voltammetry

We consider theoretically a specific electrochemical-catalytic mechanism associated with reversible regenerative chemical reaction, under conditions of cyclic staircase voltammetry (CSV). We suppose scenario in which two electrochemically inactive substrates “S” and “Y”, together with initial electrochemically active reactant Ox are present in voltammetric cell from the beginning of the experiment. Substrate “S” selectively reacts with initial electroactive reactant Ox and creates electroactive “product” Red (+ Y) in a reversible chemical fashion. The initial chemical equilibrium determines the amounts of Ox and Red available for electrode transformation at the beginning of the electrochemical experiment. Under conditions of applied potential, the electrode reaction Ox(aq) + ne– ⇋ Red(aq) occurs, producing flow of electric current. Under such circumstances, the chemical reaction coupled to the electrochemical step causes a regeneration of initial electroactive species during the time-frame of current-measuring segment in CSV. The features of cyclic voltammograms get significantly affected by the kinetics and thermodynamics of reversible regenerative reaction. We elaborate several aspects of this specific electrode mechanism, and we focus on the role of parameters related to chemical step to the features of calculated voltammograms. While we provide a specific set of results of this particular mechanism, we propose methods to get access to relevant kinetic and thermodynamic parameters relevant to regenerative chemical reaction. The results elaborated in this work can be valuable in evaluating kinetics of many drug-drug interactions, but they can be relevant to study interactions of many enzyme-substrate systems, as well.

In Situ Growth of CuWO4 Nanospheres over Graphene Oxide for Photoelectrochemical (PEC) Immunosensing of Clinical Biomarker

Procalcitonin (PCT) protein has recently been identified as a clinical marker for bacterial infections based on its better sepsis sensitivity. Thus, an increased level of PCT could be linked with disease diagnosis and therapeutics. In this study, we describe the construction of the photoelectrochemical (PEC) PCT immunosensing platform based on it situ grown photo-active CuWO4 nanospheres over reduced graphene oxide layers (CuWO4@rGO). The in situ growth strategy enabled the formation of small nanospheres (diameter of 200 nm), primarily composed of tiny self-assembled CuWO4 nanoparticles (2–5 nm). The synergic coupling of CuWO4 with rGO layers constructed an excellent photo-active heterojunction for photoelectrochemical (PEC) sensing. The platform was then considered for electrocatalytic (EC) mechanism-based detection of PCT, where inhibition of the photocatalytic oxidation signal of ascorbic acid (AA), subsequent to the antibody–antigen interaction, was recorded as the primary signal response. This inhibition detection approach enabled sensitive detection of PCT in a concentration range of 10 pg·mL−1 to 50 ng.mL−1 with signal sensitivity achievable up to 0.15 pg·mL−1. The proposed PEC hybrid (CuWO4@rGO) could further be engineered to detect other clinically important species.

The Effect of Sulfuric Acid Concentration on the Physical and Electrochemical Properties of Vanadyl Solutions

The effects of sulfuric acid concentration in VO2+ solutions were investigated via electrochemical methods and electron paramagnetic resonance. The viscosity of solutions containing 0.01 M VOSO4 in 0.1–7.0 M H2SO4 was measured. Diffusion coefficients were independently measured via electrochemical methods and electron paramagnetic resonance (EPR), with excellent agreement between the techniques employed and literature values. Analysis of cyclic voltammograms suggest the oxidation of VO2+ to VO2+ is quasi-reversible at high H2SO4 concentrations (>5 mol/L), and approaching irreversible at lower H2SO4 concentrations. Further analysis reveals a likely electrochemical/chemical (EC) mechanism where the H2SO4 facilitates the electrochemical step but hinders the chemical step. Fundamental insights of VO2+/H2SO4 solutions can lead to a more comprehensive understanding of the concentration effects in electrolyte solutions.