Enhanced visible-light-induced photocatalytic activity of α-Fe2O3 adsorbing redox enzymes

AbstractWe report fabrication of hybrid photocatalyst composed of an n-type semiconductor (α-Fe2O3) and a redox enzyme (horseradish peroxidase; HRP), and its performance for oxidation of luminol in an aqueous solution. The hybrid photocatalyst is simply formed via physical adsorption of HRP to an α-Fe2O3 sintered body. Under visible light irradiation, the bare α-Fe2O3 with a narrow bandgap photocatalytically oxidizes luminol along with blue emission that can be used as an indicator of the photocatalytic performance. The blue emission is largely strengthened after the adsorption of HRP, demonstrating that the presence of enzyme improves apparent photocatalytic activity of α-Fe2O3. The favorable effect is derived from synergistic oxidation of luminol by the biocatalysts (HRP) as well as by the photocatalyst (α-Fe2O3). In this paper, influence of excitation wavelength, adsorption amount of HRP, and reaction temperature on the overall photocatalytic activity are elucidated, and then a reaction mechanism of the proposed novel hybrid photocatalyst is discussed in detail

Enhanced catalytic activity of enzymes interacting with nanometric titanate nanosheets

The effect of the coexistence of titanate nanosheets (TNS) with nanometric lateral dimensions (ca. 3 nm), which were prepared through a hydrolysis reaction of titanium tetraisopropoxide, on the catalytic activity of horseradish peroxidase (HRP) was investigated as a function of solution pH. Especially in diluted HRP solutions with a pH range of 7-8, enzymatic reaction rate, i.e. maximum velocity (Vmax), in the conventional Michaelis-Menten equation, was significantly enhanced more than 2 times in the presence of TNS. In contrast, the increase in Vmax was not very large in acidic (pH = 4.0) and basic solutions (pH = 9.0). It was demonstrated that the TNS brought about peptization of aggregates composed of several HRP molecules in a diluted solution, causing an increase in the apparent HRP concentration participating in the enzymatic reaction. Moreover, the TNS activated superoxide dismutase (SOD) with O2 - scavenging performance

Geranylgeranylacetone selectively binds to the HSP70 of Helicobacter pylori and alters its coccoid morphology

Geranylgeranylacetone (GGA) is used to treat patients suffering from peptic ulcers and gastritis. We examined the effect of GGA on Helicobacter pylori, which is a causative factor of gastrointestinal diseases. Previously, we have reported that GGA binds specifically to the molecular chaperone HSP70. In this paper, we report that GGA bounds to H. pylori HSP70 (product of the DnaK gene) with 26-times higher affinity than to human HSP70, and induced large conformational changes as observed from surface plasmon resonance and circular dichroism. Binding of GGA suppressed the activity of the H. pylori chaperone. GGA also altered several characteristics of H. pylori cells. GGA-treated cells elicited enhanced interleukin-8 production by gastric cancer cell lines and potentiated susceptibility to complement as compared to untreated cells. GGA also caused morphological alterations in H. pylori as reflected in fewer coccoid-like cells, suggesting that GGA converts H. pylori to an actively dividing, spiral state (vegetative form) from a non-growing, coccoid state. This morphological conversion by GGA resulted in accelerated growth of H. pylori. These results suggest a model in which GGA sensitizes H. pylori to antibiotic treatment by converting the cells to an actively growing state

Magnetically applicable layered iron-titanate intercalated with biomolecules

We have prepared bio-inorganic nanohybrids consisting of magnetic inorganic nanolayers (iron-titanate) and protein molecules via exfoliation-restacking process in solution. It was found that the protein molecules were electrostatically and spontaneously incorporated into the interlayer space of the inorganic layered structure by adjusting the pH of the solution appropriately. The binding studies demonstrated the high affinity of the iron-titanate nanolayers for the proteins, and the immobilized protein preserved its activity after the hybridization. The catalytic activity measurement and magnetic separation experiment indicate the formation of magnetically applicable inorganic layer-biomolecule nanohybrids. The magnetic layer-biomolecule nanohybrid developed here would be a novel conspicuous material which shows different properties from those of conventional biomolecule-immobilized magnetic particles

Selective Chemical Labeling of Proteins with Small Fluorescent Molecules Based on Metal-Chelation Methodology

Site-specific chemical labeling utilizing small fluorescent molecules is apowerful and attractive technique for in vivo and in vitro analysis of cellular proteins,which can circumvent some problems in genetic encoding labeling by large fluorescentproteins. In particular, affinity labeling based on metal-chelation, advantageous due to thehigh selectivity/simplicity and the small tag-size, is promising, as well as enzymaticcovalent labeling, thereby a variety of novel methods have been studied in recent years.This review describes the advances in chemical labeling of proteins, especially highlightingthe metal-chelation methodology

Enzyme-Mimetic Activity of Ce-Intercalated Titanate Nanosheets

Colloidal solutions of Ce-doped titanate nanosheets (Ce-TNS) with tiny dimensions (<10 nm) were fabricated through a hydrolysis reaction of titanium tetraisopropoxide and Ce­(NO₃)₃, and their annihilation activity for reactive oxygen species (ROS) was investigated. The obtained Ce-TNS had an akin crystal structure to layered tetratitanate (Ti₄O₉^2–) and Ce ions occupied interlayer space between the host layers with a negative charge. The Ce-TNS possessed a superoxide dismutase (SOD) mimetic activity for disproportionation of superoxide anion radicals (O₂^–) as target ROS. It was explained that the annihilation of O₂^– caused a valence fluctuation of Ce ions existing in the interlayer. Moreover, the activity of Ce-TNS exceeded that of CeO₂ nanoparticles recently attracting much attention as an inorganic SOD mimic. The superior performance was explained mainly by a high dispersion stability of the Ce-TNS bringing about a huge reaction area. Moreover, the Ce-TNS protected DNA molecules from ultraviolet light induced oxidative damage, demonstrating effectiveness as one of the new inorganic protecting agents for biomolecules and tissues

Photoprotein as an internal light source for a photoelectrochemical cell employing a semiconducting oxide electrode

Inorganic-bio nanocomposites combining photoproteins (aequorin, AEQ) with a Pt-doped α-Fe2O3 (Pt-α-Fe2O3) thin film could induce a photoelectrochemical reaction without an external light source. Blue emission originated from Ca2+ binding to AEQ excited the n-type semiconducting Pt-α-Fe2O3 under an anodic bias, then an anodic photocurrent was clearly observed in a basic solution

Visible-Light-Driven Enzymatic Reaction of Peroxidase Adsorbed on Doped Hematite Thin Films

The present study proposes a novel technique to control a catalytic activity of redox enzyme (horseradish peroxidase; HRP) bound to n-type oxide semiconductor by photoirradiation. The resting HRP is transformed into activated state as a result of oxidation with holes generated in valence band of the irradiated oxide semiconductor. Subsequently, the activated HRP leads to the enzymatic conversion of organic substrates accompanied by two-electron reduction to regenerate the resting state. Because the HRP is supported with a narrow band gap semiconductor (Pt-doped α-Fe₂O₃ thin film), which is prepared by means of photoelectroless deposition, gentle energy of visible light is sufficient to trigger the reaction cycle. Accordingly, the enzymatic reaction continues for longer duration than related systems operated by ultraviolet light accounting for photodenaturation of HRP. The reaction rate depends on wavelength and intensity of the incident light and intermittent light irradiation causes a clear photoswitching behavior. At the beginning, we present the formation of Pt-doped α-Fe₂O₃ thin films via the photoelectroless deposition, and then the mechanism and advantages of the proposed reaction system are clarified in detail

Visible-Light-Induced Activity Control of Peroxidase Bound to Fe-Doped Titanate Nanosheets with Nanometric Lateral Dimensions

Catalytic performance of horseradish peroxidase (HRP) electrostatically adsorbed on nanometric and semiconducting Fe-doped titanate (FT) nanosheets was successfully manipulated by visible light illumination. A colloidal solution of FT with a narrow band gap corresponding to a visible light region was fabricated through a hydrolysis reaction of metals sources. HRP could be easily bound to the FT at pH = 4 through an electrostatic interaction between them, and the formed HRP-FT was utilized for the visible-light-driven enzymatic reaction. Under exposure to visible light with enough energy for band gap excitation of the FT, catalytic activity of HRP-FT was dramatically enhanced as compared with free (unbound) HRP and was simply adjusted by light intensity. In addition, wavelength dependence of an enzymatic reaction rate was analogous to an optical absorption spectrum of the FT. These results substantiated an expected reaction mechanism in which the photoenzymatic reaction was initiated by band gap excitation of FT followed by transferring holes generated in the valence band of irradiated FT to HRP. The excited HRP oxidized substrates (amplex ultrared: AUR) accompanied by two-electron reduction to regenerate the resting state. In addition, the catalytic activity was clearly switched by turning on and off the light source