Fenton reactions localization

Transferrin, which is the major iron-transport protein, holds two Fe(III) atoms per molecule, and it accounts for nearly all the iron in plasma, where its concentration is usually 2-5x 10-5 M [149]. In cells and tissues, the iron release from transferrin would be controlled by local pH variations in the presence of Fe(III) chelators [149]. Conflicting reports have been published on the ability of superoxide to initiate transferrin-promoted Fenton reactions [154]. 

A related technique was demonstrated by Shiku et al. (91), who formed alkylsilane monolayers at glass substrates and used electrochemical generation of OH radicals at the tip via the Fenton reaction to locally destroy the SAM. Diaphorase could then be patterned on the surface by physical adsorption to the undamaged hydrophobic areas or via covalent linkages to the radical-attacked areas. The former process was imaged in feedback mode with a ferrocenyl mediator and showed a decreased current over the disk of destroyed SAM and a constant background of enzyme activity over the rest... 

Hydroxyl radical induced strand scission is used for probing of the ribose moiety. The probe is insensitive to local conformations and not useful for detailed structural predictions however, the nonselective reactivity and small size makes hydroxyl radical probing a powerful approach for footprinting proteins on RNA. Recently methods have been developed where the hydroxyl radicals are generated locally by attaching the iron ion, which catalyses the radical formation in the Fenton reaction, to specific sites on RNA binding proteins. RNA located in the neighborhood of the tethered Fe2+ will then be modified selectively.7,8... 

The decline in metabohc activity with age, oxidative stress, and the local production of oxygen radicals from the metabolism of dopamine via the Fenton reaction (Figure 20-1) may play roles in the etiology of some of these diseases. 

Chain reactions that form lipid free radicals and lipid peroxides in membranes make a major contribution to ROS-induced injury (Fig. 24.8). An initiator (such as a hydroxyl radical produced locally in the Fenton reaction) begins the chain reaction. It extracts a hydrogen atom, preferably from the double bond of a polyunsaturated fatty acid in a membrane lipid. The chain reaction is propagated when O2 adds to form lipid peroxyl radicals and lipid peroxides. Eventually lipid degradation occurs, forming such products as malondialdehyde (from fatty acids with three or more double bonds), and ethane and pentane (from the w-terminal carbons of 3 and 6 fatty acids, respectively). Malondialdehyde appears in the blood and urine and is used as an indicator of free radical damage. 

The third approach (Fig. 22C) resulted in positive patterns, i.e., in the formation of defined areas where diaphorase was selectively attached. This approach consisted of three steps. Initially, a mercapto-terminated monolayer was locally exposed to hydroxyl radicals formed via the Fenton s reaction. Two simultaneous processes occurred the monolayer in the areas exposed to the radicals was removed to form hydroxyl-terminated surface and, at the same time, the mercapto groups in the remaining area were... 

The discussed observations led to study the redox properties of the FQ. Indeed, the presence of H2O2 in the digestive vacuole of the parasite, estimated to be 15 mM [47,54] locally (this value is subject of controversy), is particularly interesting because of the presence of Fe(II) cation in the structure of FQ. Indeed, as for the Fe(II)/Fe(III) couple, it has been shown that under oxidative conditions, close to those of the digestive vacuole, FQ is capable of generating Fenton-like reactions leading to the production of hydroxyl radicals [55] ... 

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