Reductive Activation of Dioxygen by a Myoglobin Reconstituted with a Flavohemin

Abstract

We successfully converted myoglobin, an oxygen-storage hemoprotein, into an oxygen-activating hemoprotein like cytochrome P450s by replacing the native hemin with the artificially created flavohemin. The reconstituted myoglobin, rMb(1), was chacterized by ESI-TOF-mass, UV-vis, and fluorescence spectra. The 1H NMR spectrum of cyanomet rMb(1) indicates that two hemin conformers are present in a ratio of 1:1. Upon the addition of NADH to the buffer solution of rMb(1) in the presence of SOD and catalase, the oxymyoglobin was rapidly formed. As compared with the formation of the oxygenated native myoglobin in the presence of 10-N-(acetylaminoethyl)isoalloxazine, the rate constant of the oxyheme formation in rMb(1) is 6 times larger. This is because the flavin covalently linked to the terminal heme propionate functions as an effective mediator of an electron transfer from NADH to the hemin in rMb(1). Furthermore, rMb(1) shows the deformylation activity, when 2-phenylpropionaldehyde (2-PPA) was employed as a substrate. This result indicates that the oxyheme is reductively activated to Fe(III)-peroxoanion (Fe(III)-O22-). The result in this report is the first example of the activation of dioxygen by myoglobin. This study shows the utility of the replacement of the native hemin with a chemically modified one for the functionalization of myoglobin.