An electrochemical investigation of ligand-binding abilities of film-entrapped myoglobin

Electrochemical Assay of Human Islet Amyloid Polypeptide and Its Aggregation

Square wave voltammetry is used in this work to detect human islet amyloid polypeptide (hIAPP) by using the oxidized signal of the tyrosine residue in hIAPP. A detection limit of 1×10^-6 M for hIAPP has been obtained. A kinetic study of the aggregation process has been carried out according to the relationship between the anodic peak current in the square wave voltammograms of hIAPP and the incubation period. The results show that the nucleation starts in the first hour of incubation and then, during the next two hours, aggregation may occur rapidly. hIAPP can therefore be monitored with a label-free electrochemical method with low detection limit and high sensitivity. This electrochemical method can be also utilized to study the kinetics of hIAPP aggregation, and it may be also employed to study the conformational changes of the polypeptide.

Preliminary electrochemical studies of the flavohaemoprotein from Ralstonia eutropha entrapped in a film of methyl cellulose: Activation of the reduction of dioxygen

A flavohaemoprotein (FHP) from Ralstonia eutropha, obtained in a pure and active form, has been entrapped in a film of methyl cellulose on the electrode surface and gives a stable and reproducible electrochemical response at pH 7.00 when subject to cyclic voltammetry using a glassy carbon electrode. To our knowledge, no previous direct electrochemistry had been achieved with a bacterial flavohaemoglobin, which possess both a FAD and a haem. A single couple is observed which is assigned to the haem moiety of the protein, since the same result is obtained with a semi-apo form of the protein deprived of FAD (semi-apo FHP). The data collected were further confirmed by potentiometry with a platinum electrode, and the homogeneous electron transfer rate estimated by double potential step chronocoulometry at a bare glassy carbon electrode in the presence of methyl viologen (MV). The presence of FAD in the holoprotein is easily confirmed by UV-Vis spectrophotometry, but its expected electron relay role remains elusive. The protein activates the reduction of dioxygen by about 400 mV, the reduction current being proportional to the concentration of dioxygen up to 10% in volume in the gas mixture.

Electrochemical and ligand binding studies of a de novo heme protein

Heme proteins can perform a variety of electrochemical functions. While natural heme proteins carry out particular functions selected by biological evolution, artificial heme proteins, in principle, can be tailored to suit specified technological applications. Here we describe initial characterization of the electrochemical properties of a de novo heme protein, S824C. Protein S824C is a four-helix bundle derived from a library of sequences that was designed by binary patterning of polar and nonpolar amino acids. Protein S824C was immobilized on a gold electrode and the formal potential of heme-protein complex was studied as a function of pH and ionic strength. The binding of exogenous N-donor ligands to heme/S824C was monitored by measuring shifts in the potential that occurred upon addition of various concentrations of imidazole or pyridine derivatives. The response of heme/S824C to these ligands was then compared to the response of isolated heme (without protein) to the same ligands. The observed shifts in potential depended on both the concentration and the structure of the added ligand. Small changes in structure of the ligand (e.g. pyridine versus 2-amino pyridine) produced significant shifts in the potential of the heme-protein. The observed shifts correlate to the differential binding of the N-donor molecules to the oxidized and reduced states of the heme. Further, it was observed that the electrochemical response of the buried heme in heme/S824C differed significantly from that of isolated heme. These studies demonstrate that the structure of the de novo protein modulates the binding of N-donor ligands to heme.

Electron transfer reactivity and the catalytic activity of horseradish peroxidase incorporated in dipalmitoylphosphatidic acid films

Horseradish peroxidase (HRP) was incorporated in dipalmitoylphosphatidic acid (DPPA) to form a film and the film was modified on pyrolytic graphite electrode. UV-Vis spectra suggested that HRP in the film could keep its secondary structure similar to the native state. A pair of stable, well-defined, and quasi-reversible cyclic voltammetric peaks was observed with the formal potential at -276.2 mV (vs. saturated calomel electrode), characteristic of heme Fe(III)/Fe(II) redox couple of HRP. The apparent heterogeneous electron transfer rate constant and other electrochemical parameters were presented. The catalytic activity of HRP in DPPA film toward oxygen, hydrogen peroxide and nitric oxide were also examined.

Third-generation biosensors based on the direct electron transfer of proteins

Recent progress in third-generation electrochemical biosensors based on the direct electron transfer of proteins is reviewed. The development of three generations of electrochemical biosensors is also simply addressed. Special attention is paid to protein-film voltammetry, which is a powerful way to obtain the direct electron transfer of proteins. Research activities on various kinds of biosensors are discussed according to the proteins (enzymes) used in the specific work.

Electrochemical investigation of redox thermodynamics of immobilized myoglobin: ionic and ligation effects

In this study, we investigated redox thermodynamics of myoglobin as well as the ionic (phosphate ions) and ligation (imidazole) effects via a dynamic electrochemical approach. We employed a previously established system that features nonmediated, direct electrochemistry of myoglobin and myoglobin in an immobilized state (i.e., diffusionless electrochemistry). Thermodynamics parameters were obtained by measuring redox potential (E degrees ') of myoglobin at varied temperature (T), in the presence and in the absence of specific ions or axial ligands. As a step further, we evaluated contributions from allosteric effect and axial iron ligation by partitioning E degrees ' changes into entropic and enthalpic terms. Compensation phenomena between the entropic and enthalpic changes were observed in all these cases. On the basis of these studies, we also correlated these phenomena to possible structural variations.

An electrochemical study of hemoglobin in water–glycerol solutions

The effect the composition of a water-glycerol mixture has on the electrochemical properties of hemoglobin (Hb) is studied. With the increased glycerol concentrations, the peak-to-peak separation of hemoglobin is found to increase from approximately 40 to 200 mV, with the apparent standard potential of hemoglobin negatively shifted, which demonstrate that the electron-transfer activity of hemoglobin will decrease at relatively high glycerol concentrations and the oxidized state of hemoglobin will be more stable with the increasing glycerol concentrations. Meanwhile, the electrocatalytic activity of hemoglobin to hydrogen peroxide, as well as the binding of ligands or effectors to hemoglobin in the presence of glycerol, are also been investigated. Our studies indicate that glycerol will decrease the electrocatalytic activity of hemoglobin, while have little effect on the microenvironment around the heme site.