Radical peroxyl tyrosine phenoxyl

EPR spectroscopy has demonstrated that the oxidation of the globin occurs ultimately at a tyrosine residue, resulting in the formation of a tyrosine-phenoxyl radical this species is postulated to react subsequently with oxygen to give a tyrosine-peroxyl radical. Studies have shown that both of these species are accessible to components in bulk solution, i.e. they are located on the surface of the protein [47-49]. Ferryl haem protein radical from myoglobin and haemoglobin can react with membranes [33,45,50] and lipoproteins [51-... 

It has been proposed that the second oxidizing equivalent is accepted by tyrosine-103 on the surface of the protein (Ortiz de Montel-lano, 1983) forming a tyrosine phenoxyl radical which rapidly takes up oxygen forming the peroxyl species (Davies, 1990) as depicted in Fig. 4.4. 

Fig. 4.4. Scheme for postulated formation of the tyrosine phenoxyl and peroxyl radical... 

Jonsson M, Lind J, Reitberger T, Eriksen TE, Merenyi G (1993) Free radical combination reactions involving phenoxyl radicals. J Phys Chem 97 8229-8233 Kapoor SK, Gopinathan C (1992) Reactions of halogenated organic peroxyl radicals with various purine derivatives, tyrosine, and thymine a pulse radiolysis study. Int J Chem Kinet 24 1035-1042 Khaikin Gl, Neta P (1995) Formation and reactivity of vinylperoxyl radicals in aqueous solutions. J Phys Chem 99 4549-4553... 

Aliphatic alkoxyl radicals have reduction potentials of about 1600 mV vs SHE at pH 7 making them better oxidising agents than alkyl peroxyl radicals (E 1000 mV SHE) [130], Phenoxyl radicals usually have even lower reduction potentials, e.g. phenoxyl radical (CsHsO ) with E7 900 mV vj SHE and tocopheroxyl radical with E 500 mV vj SHE [130], and these can also be produced in vivo via the oxidation of phenols, such as the amino acid tyrosine, flavenoids and other phenolic antioxidants (e.g. tocopherols), or via the reduction of quinones. 

---