Radical cation protein

This suggests the possible deleterious effects of carotenoids, for example, on membrane proteins, if, following a radical scavenging reaction, the radical cations so formed are not efficiently repaired. 

Long-range ET rates have been measured in c/ccp complexes [73, 74] the reactions between cyt c and Feccp [ES is the oxidation product of Fe(II)ccp and peroxide it has two oxidizing equivalents, namely, Fe(IV)0 and a protein-based organic radical cation] are given in Eq. (3) ... 

A similar pattern of reactivity has been observed by Burrows and coworkers for the reaction between A -acetyllysine methyl ester (Lys) and dG. This reaction was studied in order to gain an understanding of structural aspects of DNA-protein cross-links (DPCs). These cross-links are regarded as a common lesion of oxidative damage to cells, but remain, from a chemical point, a poorly understood DNA lesion. As pointed out by Burrows, oxidation of protein-DNA complexes should occur preferentially at the primary amines since these sites have a lower oxidation potential (1.1 V vs. NHE, pH 10) than G. While protonation of the primary amine inhibits the oxidative process, transient deprotonation of a lysine residue would give rise to a lysine aminyl radical (or aminium radical cation). Using... 

Peroxidases are haem proteins that are activated from the ferric state to one-electron oxidants by H202. They play a significant role in the generation of radicals from xenobiotics. The compound I state contains one oxidising equivalent as an oxoferryl-haem entity and the second as a porphyrin -radical cation. Upon the oxidation of a substrate the porphyrin radical is repaired, giving the compound II. Reduction of the oxoferryl haem back to the ferric state by a second substrate molecule completes the enzyme cycle. In addition to the classical peroxidases, several other haem proteins display pseudo-peroxidase activity. The plant enzyme horseradish peroxidase (HRP) is often employed in model systems. 

Schuster GB, Landman U (2004) The mechanism of long-distance radical cation transport in duplex DNA Ion-gated hopping of polaron-like distortions. Top Curr Chem 236 139-161 Schussler H, Jung E (1989) Protein-DNA crosslinks induced by primary and secondary radicals. Int J Radiat Biol 56 423-435... 

The peroxidase activity of PGHS is comparable to that of better known peroxidases such as horseradish peroxidase (HRP). The catalytic cycle of HRP is shown in Figure 5 [9], Its first step is the formation of an intermediate very often found in hemoproteins by transfer of an oxygen atom from various oxygen atom donors to the Fe(III) heme (Eq. 6). It is a high-valent iron-oxo species, at least formally a Fe(V)=0 complex. In fact, the detailed electronic structure of this intermediate depends on the environment of the heme provided by the protein. In HRP, this intermediate (called compound I) is a (porphyrin radical-cation)-Fe(IV)=0 complex, as shown by many spectroscopic techniques [9],... 

Furukawa N,Sato S (1999) New Aspects of Hypervalent Organosulfur Compounds. 205 89-129 Gilmore MA, Steward LE, Chamberlin AR (1999) Incorporation of Noncoded Amino Acids by In Vitro Protein Biosynthesis. 202 77 - 99 Glass RS (1999) Sulfur Radical Cations. 205 1 - 87 Gobbi L, see Diederich F (1999) 201 43-129... 

Artificial electron carriers are recognizable by the active sites of different redox enzymes and specifically biocatalysts containing Fe of Mo sulfur clusters as active sites. Bipyridinium radical cations, i.e. methyl viologen radical, MV+, exhibit proper electrical and size properties to penetrate into protein structures and to mediate reduction processes at the enzymes active sites. 

Hofmann et al.361 have obtained evidence that glycolaldehyde can interact with e-amino groups to crosslink proteins with generation of colour due to pyrazinium radical cations (cf. CROSSPY 84) under physiological conditions. This has direct bearing on, for example, cataract formation. 

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... 

In view of the formation of a highly reactive Compound I ferryl species, and the fact that the porphyrin radical cation of this intermediate is reduced in enzymes such as CcP by a protein residue, it is not surprising that permanent covalent modifications are autocatalytically introduced into some protein frameworks. Two examples of autocatalytic protein modification, those of LiP and the catalase-peroxidases, are summarized here to illustrate the maturation of peroxidase protein structures that can have important functional consequences. 

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