Cell redox cycling

From the point of view of the redox properties of the formed complex, Merkofer et al. [2006] have studied the Fenton reaction 18 catalyzed by different iron chelators and concluded that a Fe-complex can participate in cell redox cycling only when two conditions are fulfilled (i) the oxidized complex (ligand-M(" + 1 +) can be reduced by a physiologically relevant compound [e.g., NAD(P)H] [Pierre et al., 2002], then the 0 (Ligand M( +i)+/Ligand M +) is higher... 

Ayaz, M., and Turan, B. 2006. Selenium prevents diabetes-induced alterations in [Zn2+]j and met-allothionein level of rat heart via restoration of cell redox cycle. Am. J. Physiol. Heart Circ. Physiol. 290 H1071-H1080. 

The effect of prolonged antioxidant therapy in relation to normal physiological processes (for example, redox cycling, cell-cell signalling, transcription factor activation) must be assessed. It is conceivable that the overload of one antioxidant by dietary supplementation (for example, a-tocopherol) may shift the levels of other antioxidants (for example, by decreasing ascorbate and /3-carotene concentrations), with unknown consequences. To assess the potential for lipid-soluble antioxidant treatment in inflammatory diseases such as RA, further investigations into these questions will be needed. 

Hiraishi, H., Razandi, M., Terano, A. and Ivey, K.J. (1990). Antioxidant defenses of culture gastric mucosal cells against toxic oxygen metabolites. Role of glutathione redox cycle and endogenous catalase. Gastroenterology 98, A544. 

Elevated O2 concentrations Exposure to activated phagocytic cells Exposure to redox cycling drugs (e.g. alloxan, paraquat, menadione)... 

While this anode is not useful in the context of implantable fuel cells, it is of interest because methanol is an attractive anodic fuel due to its availability and ease of transport and storage. The oxidation of one equivalent of methanol requires the reduction of three equivalents of NAD+ to NADH. As the NADH cofactor itself is not a useful redox mediator, a benzylviologen/diaphorase redox cycle, with a redox potential of 0.55 V vs SCE at pH 7, was used to regenerate NAD+ for use by the dehydrogenases, as depicted in Fig. 12.10. 

Gardner et al. [165] have shown that the redox-cycling agent phenazine methosulfate (PMS), mitochondrial ubiquinol-cytochrome c oxidoreductase, or hypoxia inactivated aco-nitase in mammalian cells. It has been proposed that the inactivation of aconitase is mediated by superoxide produced by prooxidants because the overproduction of mitochondrial MnSOD protected aconitase from inactivation by the prooxidants mentioned above except hyperoxia. Later on, the reaction of superoxide with aconitases began to be considered as one of the most important ways to NTBI generation in vivo. 

Sarantaridis D and Atkinson A. Redox cycling of Ni-based solid oxide fuel cell anodes A review. Fuel Cells 2007 7 246-258. 

Once in the serum, aluminium can be transported bound to transferrin, and also to albumin and low-molecular ligands such as citrate. However, the transferrrin-aluminium complex will be able to enter cells via the transferrin-transferrin-receptor pathway (see Chapter 8). Within the acidic environment of the endosome, we assume that aluminium would be released from transferrin, but how it exits from this compartment remains unknown. Once in the cytosol of the cell, aluminium is unlikely to be readily incorporated into the iron storage protein ferritin, since this requires redox cycling between Fe2+ and Fe3+ (see Chapter 19). Studies of the subcellular distribution of aluminium in various cell lines and animal models have shown that the majority accumulates in the mitochondria, where it can interfere with calcium homeostasis. Once in the circulation, there seems little doubt that aluminium can cross the blood-brain barrier. 

Robustness requires a low sensitivity to what might cause permanent damage or degradation of the SOFC system and, hence, the cell - for excursions outside the normal operating window, contaminants in the fuel and the air, thermal and reduction-oxidation (redox) cycling of the anode. 

The most noteworthy multistage element cycles in which bacteria play important roles are the nitrogen and sulfur redox cycles. The fixation of nitrogen is a reductive process that provides organisms with nitrogen in a form usable for the synthesis of amino acids, nucleic acids, and other cell constituents. In essence, the overall conversion to the key intermediate, ammonia, can be represented as ... 

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