Electrochemical Generation and Reactions of Ferrylmyoglobins in Water and Microemulsions

Abstract

Ferrylmyoglobin species, which are active oxidant forms of the protein myoglobin, were obtained by electrochemical reduction of metmyoglobin [MbFe III ] in the presence of oxygen in aqueous neutral buffer and in microemulsions of oil, water, and cationic surfactant. Reduction of myoglobin at -0.4 V vs SCE catalyzed the reduction of oxygen to hydrogen peroxide at the electrode. Hydrogen peroxide oxidizes metmyoglobin in solution to give the radical ferrylmyoglobin • X-MbFe IV dO, which is known to decay rapidly to the non-radical MbFe IV dO. This complex reduction-oxidation process converted nearly all of the 30 µM myoglobin in a spectroelectrochemical cell to ferrylmyoglobins in 15 min in pH 7.3 buffer and in 18 min in microemulsions. Characteristic ferryl heme absorbance bands near 421, 548, and 584 nm were used to identify products. Confirmation of ferrylmyoglobins was provided by reductions to metmyoglobin with ascorbate and by myoglobin-mediated electrochemical epoxidation of styrene. Fiftyfold higher yields of styrene oxide and benzaldehyde were achieved in a microemulsion compared to electrochemical or chemical methods in pH 7.4 buffer. The electrochemical approach described may also prove useful for investigating active catalytic species of heme enzymes such as cytochrome P450.

Electronic properties of the highly ruffled heme bound to the heme degrading enzyme IsdI

“…In the absence of IsdI, a peak for direct reduction of dioxygen occurs below −200 mV, we attribute the intense reduction wave observed in the presence of IsdI and dioxygen to the catalytic reduction of O 2 by IsdI. Similar catalytic reduction of dioxygen is also observed for the molten globule state myoglobin [pH 4.8 (37)] and hemoglobin and myoglobin entrapped in methyl cellulose films (38). For the globins, this catalytic peak is attributed to the following reactions:…”

Myoglobin‐Clay Electrode for Nitric Oxide (NO) Detection in Solution

“…The reason for this can be attributed to the autoxidation of Mb/Fe 2 by residual oxygen or hydrogen peroxide formed by oxygen reduction. This behavior has also been found for Mb in solution on pyrolytic graphite electrodes [54].…”

Carbon Nanotubes as Suitable Electrochemical Platforms for Metalloprotein Sensors and Genosensors

“…Fe(II) has a very high affinity for oxygen and the latter process is immediately followed by a fast reaction of Protein-Fe(II) with oxygen. (Nakajima, 1987;Onuoha, 1997;Zhang, 2002).…”

“…The catalytic reduction of H 2 O 2 exhibits a behavior similar to the one found with oxygen, which suggests that the reaction mechanisms could be similar. Several plausible explanations have been provided in the literature (Nakajima, 1987;Onuoha, 1997;Zhang, 2002), under the assumption that H 2 O 2 can act as an oxidant or reductant agent. It has been suggested that H 2 O 2 reacts with MbFe(III) to give an oxyferryl radical ( • MbFe(IV)=O) which can react again with H 2 O 2 to produce oxygen and Mb(III).…”