Electron Spin Resonance Spectra of Free Radicals Formed in the Reaction of Metmyoglobins with Ethylhydroperoxide1

• Main Authors: Kazuo Harada, Isao Yamazaki
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1986
• Subjects: Sperm whale
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1030.8370; http://jb.oxfordjournals.org/content/101/1/283.full.pdf

Free radicals of myoglobins were measured at room temperature with an ESR spectrometer equipped with a flow apparatus. When horse heart MetMb was mixed with an equimolar amount of ethyl hydroperoxide (EtOOH), a well resolved ESR spectrum with 6 lines and a shoulder was observed. It reached a maximum in a few seconds and decayed with a half-life of about 10 s when the final concen-trations of MetMb and EtOOH were 200 /*M. This decay rate was the same at a MetMb concentration of 50 fiM. The maximum molar radical concentration amounted to about half of the total myoglobin. In the case of sperm whale myo-globin, a similar 6-line spectrum reached a maximum in 1 s and decayed with a half-life of a few seconds. In this case, however, a small and poorly resolved doublet spectrum remained, the half-life of which was about 8 min. An effect of O, on the signal decay was evident for horse heart myoglobin, but not for sperm whale myo-globin. It has been reported from several laboratories (/-6) that a free radical is formed during the reaction of H,O, or EtOOH with MetHb and MetMb. This free radical is assumed to be formed in amino acid residues on an attack by the HO- or EtO-radical, which are products of homolytic cleavage of the O-O bond of hydroperoxides on the heme iron (7, 8). MetMb+H,O,—>Ferryl myoglobin + HO•