The structure and peroxidase activity of myoglobin in alcoholic solvents

Two-dimensional layered WS2 nanosheets as peroxidase mimetics in a colorimetric chemosensor for simple and rapid detection of acetone

Two-dimensional (2D) nanomaterials with catalytic activity have attracted considerable attention from researchers, but their application in the detection of hazardous substances needs to be further expanded. Herein, layered tungsten sulfide (WS₂) nanosheets with peroxidase-mimicking activity were used to construct a colorimetric chemosensor for rapid detection of acetone. WS₂ nanosheets can decompose H₂O₂ to generate hydroxyl radicals (·OH), which will further oxidize o-phenylenediamine (OPD) through hydrogen atom transfer (HAT) to form the yellow product 2,3-diaminophenazine. Acetone can block the HAT from OPD to ·OH, thus causing obvious inhibition of the peroxidase activity of WS₂ nanosheets, making the solution appear pale yellow or even colorless. The investigation of catalytic kinetics indicates that the catalytic reaction consists of the 'ping pong' mechanism, and the regulatory effect of acetone on WS₂ nanosheets is confirmed to be an irreversible inhibition. The chemosensor can easily distinguish a trace amount of acetone by the naked eye in less than 20 min, and has a limit of detection for acetone of as low as 3.08 mg  l^-1. The application in actual samples displays the accuracy and stability of the chemosensor, suggesting that such a method is promising for acetone detection.

Hemoglobins from Scapharca subcrenata (Bivalvia: Arcidae) likely play an bactericidal role through their peroxidase activity

Hemoglobin (Hb) is an iron-containing respiratory protein present in all vertebrates and some invertebrates. The blood clam Scapharca subcrenata is one of the few invertebrates that have Hb-containing red hemocytes. In this study, we purified Hb (Ss-Hb), including Ss-HbI and Ss-HbII, from S. subcrenata hemocytes using gel chromatography with a recovery rate of 70.71%, and then characterized their peroxidase activities. Both Ss-Hbs possessed peroxidase activity with high affinity to the substrates guaiacol and H₂O₂. Moreover, both Ss-Hbs had structural similarities, such as type b heme, proximal histidine (His), distal His, and heme pocket arginine (Arg), with other peroxidases. The optimal peroxidase activity of both Ss-Hbs was at pH 5 and 35 °C, but this was inhibited in the presence of Cu²⁺ and Fe²⁺. Ss-Hbs produced [Formula: see text] in the presence of H₂O₂. β-phenylethylamine, a substrate of peroxidase, increased the [Formula: see text] generation, while Cu²⁺, an inhibitor of peroxidase, inhibited this reaction. These results indicated that the peroxidase cycle of Ss-Hb was involved in the production of [Formula: see text] . A large amount of [Formula: see text] may be generated by the peroxidase cycle if the substrate is sufficient. During the incubation of Ss-Hbs with Bacillus subtilis, it was speculated that trace H₂O₂, probably from autoxidation of Ss-Hbs or generated by B. subtilis, started the peroxidase cycle of Ss-Hb. and produced a large amount of [Formula: see text] in the presence of sufficient substrate in the culture medium. It is therefore reasonable to assume that Ss-Hbs played an antibacterial role owing to their peroxidase activity, which produced [Formula: see text] .