Electrochemical investigation of the chloride effect on hemoglobin

Investigation on the conformation change of hemoglobin immobilized on MPA-modified electrode by electrochemical method

The conformation change of bovine hemoglobin (Hb) during the unfolding process induced by urea and acid was investigated by an electrochemical method. Hb unfolding induced by urea of different concentrations was realized by bonding Hb onto a 3-mercaptopropionic acid (MPA) modified gold electrode. The difference in unfolding percentage showed that the Hb unfolding induced by urea was a two-step, three-state transition process, while the unfolding induced by acid was a two-state transition process. The results obtained by the electrochemical method coincided closely with those obtained by UV-vis spectroscopy and fluorescence spectroscopy. Some thermodynamic parameters during the conformational change were also calculated to study the intermediate state during the Hb unfolding process. The present work may lead to an easy and effective way to study metalloproteins unfolding, and holds great promise for the design of novel sensitive biosensors.

Investigation of the chloride effect on hemoglobin by adsorptive transfer voltammetry

A strategy of ex situ electrochemical method has been proposed for investigating the chloride effect on hemoglobin (Hb). Unlike the common electrochemical method that measures the chloride effect on Hb in bulk solution (in situ), the effects of chloride anion on Hb were investigated ex situ by adsorptive transfer voltammetry (AdTV) in this work. Gold electrode modified by self-assembled monolayer of 3-mercaptopropanoic acid (AuE/MPA) was prepared and then incubated in a series of Hb solutions containing different concentrations of chloride anion for adsorbing Hb-Cl (AuE/MPA/Hb-Cl). The resulting electrode was then measured in phosphate buffer solution by cyclic voltammetry. The corresponding voltammograms showed obvious promotion of the direct electron transfer of Hb with remarkable increase of peak currents, decrease of peak-to-peak separations, and negative shift of the formal potentials. As complementation, the adsorption behavior of Hb-Cl on AuE/MPA, the structural information of Hb-Cl, and the electrocatalytic ability of AuE/MPA/Hb-Cl toward hydrogen peroxide were investigated by surface plasmon resonance, circular dichroism spectrum, ultraviolet-visible spectrum and amperometry, respectively. The results indicate that the chloride effect resulted in more electroactive sites of Hb on the surface of electrode. Meanwhile, the specific and nonspecific interactions between Hb and chloride anion can be discriminated from the electrochemical parameters obtained by AdTV.

Electrochemistry and electrocatalytic of hemoglobin immobilized on FDU-15-Pt mesoporous materials

In this paper, the composite films of Nafion/Hb/FDU-Pt-15/PDDA were constructed by layer-by-layer assembly technique. The FDU-15-Pt mesoporous materials were synthesized and characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The resulting films were verified by electrochemical impedance spectroscopy (EIS), cyclic voltammetry and UV-vis spectroscopy. The direct electrochemical and electrocatalytic properties of hemoglobin (Hb) in the Nafion/Hb/FDU-15-Pt/PDDA films were also investigated. A pair of stable and well-defined reversible redox peaks was observed and the formal potential of Hb Fe(III)/Fe(II) redox couple was found to be -0.324 V (vs. SCE). Based on a series of optimized conditions, the films modified electrode displayed a good electrocatalytic activity to the reduction of hydrogen peroxide (H2O2), which had linear current response from 2.0 x 10(-6) M to 6.0 x 10(-2) M with the detection limit of 1.0 x 10(-6) M (S/N=3). The apparent Michaelis-Menten constant (K(m)(app)) was determined to be 0.15 mM in the range of lower concentration of H2O2. The apparent heterogeneous electron transfer rate constant (k(s)) was 1.05 +/- 0.03 s(-1). The good sensitivity, reproducibility, excellent stability and wide linear range make Nafion/Hb/FDU-15-Pt/PDDA a promising application of the preparation of third-generation biosensor.

Electrochemical investigation of the effect of some organic phosphates on haemoglobin

The effects of DPG,IHP,GTP,GDP and GMP on the structure and stability of haemoglobin were electrochemically investigated with an iodide-modified silver electrode in 0.01 M KNO 3 at pH 7.0.Anodic and cathodic peaks of haemoglobin were observed at 250 mV and 12 mV with a formal potential value of 133 mV vs.Ag/AgCl.The effects of different concentrations of DPG,IHP,GTP,GDP and GMP on the anaerobic redox reaction were determined. The results showed that DPG and IHP can lead to a positive shift in the reduction peak of haemoglobin,indicating that the oxidation peak shift of haemoglobin was small as a result of stabilization of the reduced state and destabilization of the R-like state of haemoglobin.GTP elicited a more positive shift in the cathodic and anodic peaks of haemoglobin at a higher concentration,signifying that it has a low-affinity binding site on haemoglobin.The positive shift of the cathodic and anodic peaks revealed a slight variation in the structure and indicated the unfolding of haemoglobin in the presence of high concentrations of GTP.Our study also showed that GDP and GMP did not cause significant shift the cathodic and anodic peaks of haemoglobin even at high concentrations,refuting the existence of specific GDP-and GMP-binding sites on the protein.Moreover,the iodide-modified silver electrode method proved to be easy and useful in investigating the effects of ligands or other effectors on haemoglobin in solution.

Direct electrochemistry and electrocatalysis of heme proteins entrapped in agarose hydrogel films in room-temperature ionic liquids

The electrochemistry and electrocatalysis of a number of heme proteins entrapped in agarose hydrogel films in the room-temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) have been investigated. UV-vis and FTIR spectroscopy show that the heme proteins retain their native structure in agarose film. The uniform distribution of hemoglobin in agarose-dimethylformamide film was demonstrated by atomic force microscopy. Cyclic voltammetry shows that direct electron transfer between the heme proteins and glassy carbon electrode is quasi-reversible in [bmim][PF(6)]. The redox potentials for hemoglobin, myoglobin, horseradish peroxidase, cytochrome c, and catalase were found to be more negative than those in aqueous solution. The charge-transfer coefficient and the apparent electron-transfer rate constant for these heme proteins in [bmim][PF(6)] were calculated from the peak-to-peak separation as a function of scan rate. The heme proteins catalyze the electroreduction of trichloroacetic acid and tert-butyl hydroperoxide in [bmim][PF(6)]. The kinetic parameter I(max) (maximum current at saturation concentration of substrate) and the apparent K(m) (Michaelis-Menten constant) for the electrocatalytic reactions were evaluated.