Radical protein

Stubbe J, WA van der Donk (1998) Protein radicals in enzyme catalysis. Chem Rev 98 705-762. 

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. 

The word protein was invented by Mulder, who believed that there was a protein radical that was common to all proteins. 

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. 

IV, F and Fig. 7). In catalatic mode, HPI exhibits no significant spectral change, snggesting that compoimd I has an oxidation equivalent in the form of a protein radical rather than a porphyrin radical. On the other hand, the W105F variant of HPI, which operates only in peroxidatic mode, has a porphyrin radical clearly evident in the absorbance and EPR spectra 101). 

The self-peroxidation reactions of Cu,Zn-SOD provide a particularly novel mechanism for the formation of protein radicals. Hydrogen peroxide is generated during the reaction cycle of the enzyme ... 

Low-density lipoprotein oxidation. A detailed EPR study of LDL oxidation by HRP has been reported by Pietraforte and colleagues, who reported the direct observation of the a-tocopheroxyl radical and a protein radical (g = 2.003), assigned tentatively to a tyrosyl radical and also trapped with MNP.295 Another study reported the observation of the probucol phenoxyl radical in LDL undergoing oxidation by lipoxygenase. This finding supports the assertion... 

Nonblue. These include galactose oxidase (GO) and amine oxidases (e.g., plasma amine oxidase, diamine oxidase, lysyl oxidase), which produce dihydrogen peroxide by the two-electron reduction of 02 [33], For GO (stereospecific primary alcohol oxidation), spectroscopic studies by Whittaker [70,71] suggest that the two-electron oxidation carried out by a mononuclear copper center is aided by a stabilized ligand-protein radical (i.e., (L)Cu(I) + 02 —> (L +)Cu(lI) + H202), obviating the need to get to Cu(III) in the catalytic cycle. Protein x-ray structures [33,72] reveal a novel copper protein cofactor, which would seem... 

Jarett JT, Drennan CL, Amaratunga M, Scholten JD, Ludwig ML, Matthews RG. A protein radical cage slows photolysis of methylcobalamin in methionine synthase from Escherichia coli. Bioorg Med Chem 1996 4 1237-46. 

Ruiz-Duenas FJ, Pogni R, Morales M et al (2009) Protein radicals in fungal versatile peroxidase catalytic tryptophan radical in both Compound I and Compound II and studies on W164Y, W164H and W164S variants. J Biol Chem 284 7986—7994... 

Miller VP, Goodin DB, Friedman AE et al (1995) Horseradish peroxidase Phel72Tyr mutant. Sequential formation of Compound I with a porphyrin radical cation and a protein radical. J Biol Chem 270 181413-181419... 

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