Protein-based radical

Suarez J, Ranguelova K, Jarzecki AA et al (2009) An oxyferrous heme/protein-based radical intermediate is catalytically competent in the catalase reaction of Mycobacterium tuberculosis catalase-peroxidase (KatG). J Biol Chem 284 7017-7029... 

Ivancich A, Jakopitsch C, Auer M et al (2003) Protein-based radicals in the catalase-peroxidase of Synechocystis PCC6803 a multifrequency EPR investigation of wild-type and variants on the environment of the heme active site. J Am Chem Soc 125 14093-14102... 

Although a similar Fe(IV)=0 intermediate of IDO has not yet been directly observed in the catalytic cycle of TDO, it has been trapped and characterized in the enzyme reactivation study. The ferric form of TDO can be reactivated by H202in the presence of Trp through a complex mechanism [40]. When Fe(lll)-TDO reacts with H2O2 in the absence of T rp, the Fe ion becomes EPR-silentand a protein-based radical is observed (Fig. 15.6). The free radical decays overtime, while the EPR signal of the high-spin ferric heme is restored. The ferric ion is shown by Mossbauer spectroscopy to... 

In Ae absence of external reductants, MbFe(IV)=0 decays spontaneously to MbFe(I V)=0 and MbFe(III) by pathways that are poorly understood (11,14,28-32). One of the protein-based radicals of h Fe(IV)=0, a tyrosyl phenoxyl radical, has been reported to have a half-life of 45 seconds (33), and anoAer of Aese radicals, a tryptophan-centered radical, has been found to react with dioxygen to form a peroxyl radical with a half-life of 7 seconds (33-33). 

Newman et al. (76) suggested that the peroxyl radical of MbFe(IV)=0 that was later assigned to a tryptophan residue (35) is responsible for initiation of lipid peroxidation. In contrast, Rao et al. (83) found that Fe(IV)=0 binds polyunsaturated fatty acids in the heme crevice and subsequently abstracts a bisallylic hydrogen atom prior to addition of Oj to form the lipid peroxyl radical, and diat MbFe(IV)=0 rather than the protein-based radical of MbFe(rV)=0 is Ae initiator of lipid peroxidation. 

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