Redox control mechanisms, cellular

Future research should also focus its attention on the factors/mechanisms that regulate free-radical activity in vivo. The complex interrelationship between cellular and extracellular levels of antioxidants needs to be clarified, and factors that govern the synthetic rate of the scavenging enzymes, for example, SOD or catalase will provide further insight into cellular redox control. 

In neural cells, the redox status is controlled by the thioredoxin (Trx) and glutathione (GSH) systems that scavenge harmful intracellular ROS. Thioredoxins are antioxidants that serve as a general protein disulphide oxidoreductase (Saitoh et al., 1998). They interact with a broad range of proteins by a redox mechanism based on the reversible oxidation of 2 cysteine thiol groups to a disulphide, accompanied by the transfer of 2 electrons and 2 protons. These proteins maintain their reduced state through the thioredoxin system, which consists of NADPH, thioredoxin reductase (TR), and thioredoxin (Trx) (Williams, Jr. et al., 2000 Saitoh et al., 1998). The thioredoxin system is a system inducible by oxidative stress that reduces the disulfide bond in proteins (Fig. 7.4). It is a major cellular redox system that maintains cysteine residues in the reduced state in numerous proteins. 

We have now accrued considerable evidence that reversed electron transfer provides the driving force that poises the redox couples of living cells and enables reductive syntheses.This work is still in progress, but already an understanding of the mechanisms by which energy flow drives proton current to poise both the phosphorylation state (by control of ATP synthesis) and the various cellular redox states (by control of reversed electron transfer) seems closer. 

While direct interactions of cadmium ions with DNA appear to be of little importance, interactions with proteins are of high significance. Especially the DNA repair inhibitions but also altered cell proliferation and/or diminished cell cycle control have frequently been observed at low, non-cytotoxic concentrations of cadmium, raising the question of particularly sensitive targets of cadmium ions. Relevant mechanisms include elevated levels of ROS, interactions with homeostasis and cellular functions of essential metal ions like zinc, calcium, and iron and the interference with cellular redox regulation. 

Whatever the underlying mechanism(s) of copper toxicity is it makes tight control of copper levels a cellular necessity. While cuproenzymes that catalyze oxygen transport or redox reactions have been under inves-... 

According to the endosymbiontic hypothesis mitochondria derive from ancestors that are closely related to modern purple bacteria, for example, Pseudomonas, Rhodobacter, and Paracoccus. Although mitochondria are embedded in a cellular environment with narrowly controlled conditions regarding pH, redox balance, and substrate availability, bacteria may encounter a variety of environmental conditions. A repertoire of respiratory chains and regulatory mechanisms as opposed to a single electron transfer chain allows them to cope with a variety of environments. 

Levonen AL, Landar A, Ramachandran A, Ceaser EK, Dickinson DA, Zanoni G, Morrow JD, Darley-Usmar VM (2004) Cellular mechanisms of redox cell signalling role of cysteine modification in controlling antioxidant defences in response to electrophilic lipid oxidation products. Biochem J 378(Pt 2) 373-382... 

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