Protein radical, formation

Giulivi C, Cadenas E (1998) Heme protein radicals formation, fate and biological consequences. Free Radic Biol Med 24 269-279... 

For tryptophan, there seems to be an equilibrium, which could also lead to some tryptophan radical formation and subsequent protein damage ... 

Taurog et al. [216] showed that contrary to previous suggestions, both iodination and coupling are catalyzed by the oxoferryl porphyrin Tr-cation radical of TPO Compound I and not the oxoferryl protein radical. HRP catalyzed the oxidation of bisulfite to sulfate with the intermediate formation of sulfur trioxide radical anion S03 [217] HPO, MPO, LPO, chloroperoxidase, NADH peroxidase, and methemoglobin oxidized cyanide to cyanyl radical [218],... 

Inhibition and stimulation of LOX activity occurs as a rule by a free radical mechanism. Riendeau et al. [8] showed that hydroperoxide activation of 5-LOX is product-specific and can be stimulated by 5-HPETE and hydrogen peroxide. NADPH, FAD, Fe2+ ions, and Fe3+(EDTA) complex markedly increased the formation of oxidized products while NADH and 5-HETE were inhibitory. Jones et al. [9] also demonstrated that another hydroperoxide 13(5)-hydroperoxy-9,ll( , Z)-octadecadienoic acid (13-HPOD) (formed by the oxidation of linoleic acid by soybean LOX) activated the inactive ferrous form of the enzyme. These authors suggested that 13-HPOD attached to LOX and affected its activation through the formation of a protein radical. Werz et al. [10] showed that reactive oxygen species produced by xanthine oxidase, granulocytes, or mitochondria activated 5-LOX in the Epstein Barr virus-transformed B-lymphocytes. 

Two current alternative views are available as to how remotely boimd NADPH may work. One sees its action as involving two successive one-electron oxidations (52, 53). The effectiveness of NADPH in preventing compound II formation is then due to the high reactivity of the NADP intermediate as reductant of the compound II generated in the first one-electron step. The other model (47) prefers to see NADPH as a hydride donor responsible for the almost simultaneous reduction of the ferryl iron and the protein radical species. 

Siraki, A.G., Deterding, L.J., Bonini, M.G., Jian, J., Ehrenshaft, M., Tomer, K.B. and Mason, R.P. (2008) Procainamide, but not N-Acetylprocainamide, induces protein free radical formation on myeloperoxidase a potential mechanism of agranulocytosis. Chemical Research in Toxicology, 21, 1143-1153. 

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