Direct electrochemistry and environmental sensing of rice hemoglobin immobilized at graphite electrodes

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• 作者：Beatriz Royo ; Maciej Sosna ; Aaron C. Asensio ; Jose F. Moran ; Elena E. Ferapontova
• 关键词：Heme proteins ; Electron transfer ; Rice hemoglobin ; Bioelectrocatalysis ; Ligand sensing ; oxygen ; hydrogen peroxide ; cyanide and superoxide
• 刊名：Journal of Electroanalytical Chemistry
• 出版年：2013
• 出版时间：1 September, 2013
• 年：2013
• 卷：704
• 期：Complete
• 页码：67-74
• 全文大小：1256 K

文摘

Non-symbiotic hemoglobin from rice (Oryza sativa L.), OsHb-1, with hexacoordinated rather than pentacoordinated heme and high affinity for oxygen, may have a particular role in O₂ and environmental sensing. Here, a 21 kDa monomer OsHb-1 was electrochemically studied at graphite electrodes and further probed in analysis of environmental species such as hydrogen peroxide, cyanide, and superoxide. Redox potential of the OsHb-1 heme iron was found to be ?136 mV vs. SCE, at pH 6.5, while the rate constant k_s for the heterogeneous electron transfer (ET) between graphite and OsHb-1 immobilized in the Nafion membrane at the carbon nanotubes-modified electrodes was below 0.2 s^?1. Despite sluggish ET, OsHb-1 efficiently, with current densities exceeding 2 mA cm^?2 at ?0.3 V, electrocatalyzed reduction of O₂ starting from the potentials of OsHb-1 heme. The bioelectrocatalytic reduction of O₂ was partially inhibited by CN^? thus enabling its sensing down to a 100 pM level. Peroxidase-like activity of OsHb-1 and the reaction of the superoxide anion with the heme iron of OsHb-1, in de-oxygenated solutions, were studied and analysed in terms of OsHb-1 reactivity. The results obtained indicate OsHb-1 is a sensitive tool for environmental biosensing and toxicity screening.