Modified cytochrome c/H2O2 system: spectroscopic EPR investigation of the biocatalytic behaviour

An efficient visible light controlled protein delivery system

A visible light triggered protein delivery system has been assembled through hydroxyl coordinated onto titania nanoparticles. Biomolecules such as hemoglobin (Hb) can be controlled-released from the hybrid material TiO(2)-DB-Hb by switching visible light on/off. The released Hb not only retains its senior structure but also can fulfil the enzymatic bioactivity. Controlled delivery of Hb stems from the scission of the Ti-O coordination bond with the aid of photo-inducing electron transfer property of titania.

Control of electrochemical and ferryloxy formation kinetics of cyt P450s in polyion films by heme iron spin state and secondary structure

Voltammetry of cytochrome P450 (cyt P450) enzymes in ultrathin films with polyions was related for the first time to electronic and secondary structure. Heterogeneous electron transfer (hET) rate constants for reduction of the cyt P450s depended on heme iron spin state, with low spin cyt P450cam giving a value 40-fold larger than high spin human cyt P450 1A2, with mixed spin human P450 cyt 2E1 at an intermediate value. Asymmetric reduction-oxidation peak separations with increasing scan rates were explained by simulations featuring faster oxidation than reduction. Results are consistent with a square scheme in which oxidized and reduced forms of cyt P450s each participate in rapid conformational equilibria. Rate constants for oxidation of ferric cyt P450s in films by t-butyl hydroperoxide to active ferryloxy cyt P450s from rotating disk voltammetry suggested a weaker dependence on spin state, but in the reverse order of the observed hET reduction rates. Oxidation and reduction rates of cyt P450s in the films are also likely to depend on protein secondary structure around the heme iron.

Direct Electrochemical and Spectroscopic Assessment of Heme Integrity in Multiphoton Photo-Cross-Linked Cytochrome c Structures

Multiphoton excitation (MPE) lithography offers an effective, biocompatible technique by which three-dimensional architectures comprised of proteins, enzymes, and other relevant materials may be fabricated for use in biological studies involving cellular signal transduction and neuronal networking. We present a series of studies designed to investigate the integrity of cytochrome c (cyt c) photo-cross-linked via MPE. Specifically, we have used electrochemical methods and surface-enhanced Raman spectroscopy (SERS) to determine whether photo-cross-linked cyt c retains its well-characterized Fe(II/III) heme redox activity. Cyt c is observed to retain its native FeII/III electron-transfer properties, as the apparent electron-transfer rate constant, k0ET, for cyt c photo-cross-linked onto an indium-doped tin oxide (ITO) substrate was 8.4 +/- 0.2 s-1, on the same order of magnitude as literature values though somewhat slower than other immobilized cyt c studies, most likely due to unoptimized entrapment in the photo-cross-linked matrix. SERS data reveals peaks corresponding to vibrational modes of an intact porphyrin ring with the Fe center intact. Cyt c has also been shown to demonstrate peroxidase-like activity, and we have evaluated the turnover rate of H2O2 at photo-cross-linked matrices relative to that at adsorbed monolayers of cyt c on glass substrates. The photo-cross-linked cyt c samples demonstrate apparent Michaelis-Menten parameters of Vm = 0.34 fmol/s and kcat/Km on the order of 104 s-1 M-1, in agreement with previously published results for aqueous cyt c. Fluorescence data obtained for mediated H2O2 turnover also indicated enzymatic activity specifically at photo-cross-linked cyt c structures.

Enhancing Stability and Oxidation Activity of Cytochrome c by Immobilization in the Nanochannels of Mesoporous Aluminosilicates

Hydrothermally stable and structrurally ordered mesoporous and microporous aluminosilicates with different pore sizes have been synthesized to immobilize cytochrome c (cyt c): MAS-9 (pore size 90 A), MCM-48-S (27 A), MCM-41-S (25 A), and Y zeolites (7.4 A). The amount of cyt c adsorption could be increased by the introduction of aluminum into the framework of pure silica materials. Among these mesoprous silicas (MPS), MAS-9 showed the highest loading capacity due to its large pore size. However, cyt c immobilized in MAS-9 could undergo facile unfolding during hydrothermal treatments. MCM-41-S and MCM-48-S have the pore sizes that match well the size of cyt c (25 x 25 x 37 A). Hence the adsorbed cyt c in these two medium pore size MPS have the highest hydrothermal stability and overall catalytic activity. On the other hand, the pore size of NaY zeolite is so small that cyt c is mostly adsorbed only on the outer surface and loses its enzymatic activity rapidly. The improved stability and high catalytic activity of cyt c immobilized in MPS are attributed to the electrostatic attraction between the pore surface and cyt c and the confinement provided by nanochannels. We further observed that cyt c immobilized in MPS exists in both high and low spin states, as inferred from the ESR and UV-vis studies. This is different from the native cyt c, which shows primarily the low spin state. The high spin state arises from the replacement of Met-80 ligands of heme Fe (III) by water or silanol group on silica surface, which could open up the heme groove for easy access of oxidants and substrates to iron center and facilitate the catalytic activity. In the catalytic study, MAS-9-cyt c showed the highest specific activity toward the oxidation of polycyclic aromatic hydrocarbons (PAHs), which arises from the fast mass transfer rate of reaction substrate due to its large pore size. For pinacyanol (a hydrophilic substrate), MCM-41-S-cyt c and MCM-48-S-cyt c showed higher specific activity than NaY-cyt c and MAS-9-cyt c. The result indicated that cyt c embedded in the channels of MCM-41-S and MCM-48-S was protected against unfolding and loss of activity. By increasing the concentration of the spin trapping agent, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in ESR experiments, we showed that cyt c catalyzes a homolytic cleavage of the O-O bond of hydroperoxide and generates a protein cation radical (g = 2.00). Possible mechanisms for MPS-cyt c catalytic oxidation of hydroperoxides and PAHs are proposed based on the spectroscopic characterizations of the systems.

Biocatalytic transformation of petroporphyrins by chemical modified cytochrome C

A semi-synthetic biocatalyst was prepared by a double chemical modification of cytochrome c. Free amino groups were modified with poly(ethylene glycol) while free carboxylic groups were alkylated to form methyl esters. The double chemically modified protein, PEG-Cyt-Met, oxidized synthetic porphyrins in a ternary solvent mixture composed by methylene chloride, methanol, and phosphate buffer. The highest activity was found in the ternary systems with low water content (5%). The use of relatively hydrophobic peroxides, such as tert-butyl and cumene hydroperoxides, extended the operational life of the biocatalyst, which, in turn, resulted in an extended oxidation of the substrates tested. PEG-Cyt-Met is able to transform asphaltenes, a highly recalcitrant petroleum fraction. The huge energetic resource found as asphaltene-rich deposits is the driving force to investigate and to innovate upgrading technologies, including biotechnological strategies.

Suicide inactivation of peroxidases and the challenge of engineering more robust enzymes

As the number of industrial applications for proteins continues to expand, the exploitation of protein engineering becomes critical. It is predicted that protein engineering can generate enzymes with new catalytic properties and create desirable, high-value, products at lower production costs. Peroxidases are ubiquitous enzymes that catalyze a variety of oxygen-transfer reactions and are thus potentially useful for industrial and biomedical applications. However, peroxidases are unstable and are readily inactivated by their substrate, hydrogen peroxide. Researchers rely on the powerful tools of molecular biology to improve the stability of these enzymes, either by protecting residues sensitive to oxidation or by devising more efficient intramolecular pathways for free-radical allocation. Here, we discuss the catalytic cycle of peroxidases and the mechanism of the suicide inactivation process to establish a broad knowledge base for future rational protein engineering.