pH-dependent protein conformational changes in albumin : gold nanoparticle bioconjugates: A spectroscopic study

The conformational changes of bovine serum albumin (BSA) in the albumin:gold nanoparticle bioconjugates were investigated in detail by various spectroscopic techniques including UV-vis absorption, fluorescence, circular dichroism, and Fourier transform infrared spectroscopies. Our studies suggested that albumin in the bioconjugates that was prepared by the common adsorption method underwent substantial conformational changes at both secondary and tertiary structure levels. BSA was found to adopt a more flexible conformational state on the boundary surface of gold nanoparticles as a result of the conformational changes in the bioconjugates. The conformational changes at pH 3.8, 7.0, and 9.0, which corresponded to different isomeric forms of albumin, were investigated, respectively, to probe the pH effect on the conformational changes of BSA in the bioconjugates. The results showed that the pH of the medium influenced the changes greatly and that fluorescence and circular dichroism studies further indicated that the changes were larger at higher pH.

Electrochemical and bioelectrochemistry properties of room-temperature ionic liquids and carbon composite materials

Room-temperature ionic liquids (RTILs) are liquids at room temperature and represent a new class of nonaqueous but polar solvents with high ionic conductivity. The conductivity property of carbon nanotubes/RTILs and carbon microbeads/RTILs composite materials has been studied using ac impedance technology. Enzyme coated by RTILs-modified gold and glassy carbon electrodes allow efficient electron transfer between the electrode and the protein and also catalyze the reduction Of O-2 and H2O2,

Study on mechanism of interaction between Eu3+ and microperoxidase-11

The interaction mechanism between Eu3+ and microperoxidase-II (MP-11) in the aqueous solution was investigated using the UV-vis absorption spectroscopy, cyclic voltammetry and electrospray ionization mass spectrometry. It was found that one Eu3+ ion can coordinate with two carboxyl oxygen of two propionic acid groups of the heme group in the MP-11 molecule, leading the increase in the nonplanarity of the porphyrin ring and exposure degree of Fe(III) in the heme group. Therefore, the reversibility of the electrochemical reaction and the electrocatalytic activity of MP-11 for the reduction of oxygen are increased.

Direct electrochemistry and surface plasmon resonance characterization of alternate layer-by-layer self-assembled DNA-myoglobin thin films on chemically modified gold surfaces

Alternate layer-by-layer (L-by-L) polyion adsorption onto gold electrodes coated with chemisorbed cysteamine gave stable, electroactive multilayer films containing calf thymus double stranded DNA (CT ds-DNA) and myoglobin (Mb). Direct, quasi-reversible electron exchange between gold electrodes and proteins involved the Mb heme Fe2+/Fe3+ redox couple. The formation of L-by-L (DNA/Mb), films was characterized by both in situ surface plasmon resonance (SPR) monitoring and cyclic voltammetry (CV). The effective thickness of DNA and Mb monolayers in the (DNA/Mb)l bilayer were 1.0 +/- 0.1 and 2.5 +/- 0.1 mn, corresponding to the surface coverage of similar to65% and similar to89% of its full packed monolayer, respectively. A linear increase of film thickness with increasing number of layers was confirmed by SPR characterizations. At pH 5.5, the electroactive Mb in films are those closest to the electrode surface; additional protein layers did not communicate with the electrode. CV studies showed that electrical communication might occur through hopping conduction via the electrode/base pair/Mb channel, thanks to the DNA-Mb interaction. After the uptake of Zn2+, a special electrochemical behavior, where MbFe(2+) acts as a DNA-binding reduction catalyst in the Zn2+-DNA/Mb assembly, takes place.

Hydrogen peroxide biosensor based on microperoxidase-11 entrapped in lipid membrane

A highly catalytic activity microperoxidase-11 (MP-11) biosensor for H2O2 was developed to immobilizing the heme peptide in didodecyldimethylammonium bromide (DDAB) lipid membrane. The enzyme electrode thus obtained responded to H2O2 without electron mediator or promoter, at a potential of +0.10 V versus Ag \ AgCl. A linear calibration curve is obtained over the range from 2.0 x 10(-5) to 2.4 x 10(-3) M. The biosensor responds to hydrogen peroxide in 15 s and has a detection limit of 8 x 10(-7) M (S/N = 3) Providing a natural environment with lipid membrane for protein immobilization and maintenance of protein functions is a suitable option for the design of biosensors.

Promoter effect of La3+ on the electrochemical reaction of microperoxidase-11

The effect of La3+ on the electrochemical behavior and structure of heme undecapeptide-microperoxidase-11 (MP-11)-in the aqueous solution was investigated using cyclic voltammetry, circular dichroism (CD) and UV-vis absorption spectrometry. It was found for the first time that La3+ would promote the electrochemical reaction of MP-11 at the glassy carbon (GC) electrode. This is mainly due to the fact that La3+ would induce more beta-turn and alpha-helical conformations from the random coil conformation of MP-11 and increase the non-planarity of the heme.

Surface-enhanced Raman spectroscopy of microperoxidase-11 on roughed silver electrodes

The conformation of microperoxidase-11 (MP-11) adsorbed on roughened silver electrodes was studied using surface-enhanced Fourier transform Raman spectroscopy. The results demonstrate that MP-11 was initially adsorbed via its polypeptide chain with a alpha-helix conformation, as indicated by the enhancement of the characteristic bands related to the amides I and III. The weak resonance effect of the porphyrin macrocycle in the near IR region contributes to the spectrum of the heme group. The presence of imidazole as the sixth ligand to the heme iron influences the conformation of the polypeptide chain of MP-11 on the electrode surface. Evaporation of solvent water results in an opened conformation of the adsorbed MP-11. which allows the heme group to contact the electrode surface directly.

Resonance Raman and surface-enhanced Raman spectroscopic study of microperoxidase-11

The electron transfer and structure of microperoxidase-11(MP-11) in solution and at electrode/solution interface were studied by electrochemical, resonance Raman and surface-enhanced Raman spectroscopic techniques. Results show that the central iron in heme group was six-coordinated in solution, whereas it was converted to five-coordinated state as MP-11 was adsorbed on the surface of a roughened silver electrode, due to the reorientation of MP-11 molecules. The electrochemical properties of MP-11 were directly affected by the coordination state of heme iron.

Electrochemistry and spectroscopy study on the interaction of microperoxidase-11 with lipid membrane

The interaction of microperoxidase-11 (MP11) with cationic lipid vesicles of didodecyldimethylammonium bromide (DDAB) induces an alpha -helical conformation from random coil conformations in solution and this change then makes heme macrocycle more distorted. DDAB-induced MP11 conformations were investigated by cyclic votammetry (CV), circular dichroism (CD) and UV-vis spectrometry. All results indicate that the binding of MP11 in solution to DDAB vesicles and the ordered structure formation are driven by mostly electrostatic interaction between negatively charged residues in the undecapeptide and positively charged lipid headgroups on the membrane surface. Upon binding to DDAB, its half-peak potential was also changed. The mechanism of the interaction between MP11 and DDAB was also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Synchronous fluorescence spectra of myoglobin

The synchronous fluorescence spectra of myoglobin were studies for the first time. The fluorescence peals observed in the spectra were assigned, When the wavelength interval (Delta lambda) is 80 nm, the main peak at 335 nm is originated from the tryptophan residues in the myoglobin molecule. When Delta lambda is 20 nn, the peak at 308 nm is mainly due to the tyrosine residues in the myoglobin molecule and in a small part due to the tryptophan residues. Two peaks at 322 and 596 nm were observed in the spectrum of myoglobin for Delta lambda = 40 nm. The peak at 322 nm is due to both tyrosine and tryptophan residues. The peak at 596 nm is attributed to the heme group in the myoglobin molecule.

Synchronous fluorescence spectra of hemoglobin: A study of aggregation states in aqueous solutions

The synchronous fluorescence spectra of hemoglobin solutions are reported for the first rime. The main fluorescence peaks observed in the spectra are assigned. The effect of the concentration of hemoglobin solution on the spectra is studied. Characteristic fluorescence peaks due to the dimer and tetramer of hemoglobin molecules are recognized. (C) 1998 Academic Press.

Interfacial characteristics of the self-assembly system of poly-L-lysine 3-mercaptopropionic acid gold electrode

The interfacial characteristics of poly-L-lysine (PL) attached on self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA) were studied by an electrochemical method. The results indicated that PL\MPA layer inhibited partly the diffusion process of redox species in solution, and the electrode surface behaved like a microelectrode array. Its permeation effect was also strongly affected by Mg2+. The more Mg2+ ions were added into the electrolyte solution, the greater the difficulty with which the electron transfer of potassium ferricyanide took place. The three different conformations of PL on the electrode surface had different influences on the electron transfer processes of ferricyanide. PL in random coil state hindered most strongly the electron transfer behavior of ferricyanide,while the alpha-helical PL had nearly no effect and the effect of the beta-sheet state PL was intermediate of these. (C) 1997 Elsevier Science S.A.

Cyclic voltammetry of dye-modified supported bilayer lipid membranes (s-BLMs)

The voltammetric behaviour of dye-modified supported bilayer lipid membranes is investigated. (C) 1997 Elsevier Science S.A.

The direct electrochemistry of cryo-hydrogel immobilized myoglobin at a glassy carbon electrode

A cryo-hydrogel membrane (CHM) immobilized at a glassy carbon (GC) electrode is reported for the direct electron transfer of redox proteins. The most attractive characteristics of this CHM were its hydrophilic micro-environment for incorporated proteins to retain their activities, its high ability for protection against interference of denatured and adsorbed proteins at the electrode, its potential applications for various proteins or enzymes, as well as its high mechanical strength and thermal stability. A clear well developed and stable redox wave was obtained for commercially available horse heart myoglobin without further purification, giving a peak to peak separation Delta E(p) = 93 mV at 5 mV s(-1) and the formal electrode potential E(0)' = -0.158 V (vs. Ag/AgCl). The formal heterogeneous electron transfer rate constant was calculated as k(0)' = 5.7 X 10(-4) cm s(-1) at pH 6.5, showing rapid electron transfer was achieved. The pH controlled conformational equilibria, acid state --> natural state --> basic I state --> basic II state, of myoglobin at the CHM GC electrode in the pH range 0-13.8 were also observed and are discussed in detail.