19] Ferrylmyoglobin: Formation and chemical reactivity toward electron-donating compounds

Abstract

Publisher Summary This chapter discusses several chemical and biological aspects of ferrylmyoglobin, such as its formation and absorption and electron paramagnetic resonance (EPR) spectral properties, the reactivity of the oxoferryl moiety toward different compounds with emphasis on antioxidants, and its identification and significance in complex biological systems. The oxidation of metmyoglobin by H2O2 is associated with visible absorption spectral changes consisting of an increase in absorbance in the 520-600 nm region, with main peaks at 548 and 582 nm, and a decrease at 630nm, with an isosbestic point at 618 nm. This spectral profile is ascribed to ferrylmyoglobin. The chapter provides evidence of amino acid radical in ferrylmyoglobin. Phenylalanine and tyrosine residues have been considered the primary loci of the protein free radical density. Three tyrosine residues (Tyr-103, Tyr-146, and Tyr-151) are present in sperm whale myoglobin, two residues (Tyr-103 and Tyr-146) in horse heart myoglobin, and one (Tyr-146) in kangaroo myoglobin. The amino acid radical in ferrylmyoglobin is evidenced by direct stopped-flow electron paramagnetic resonance (EPR) spectroscopy.