Plasma membrane redox system

The yeast-mediated enzymatic biodegradation of azo dyes can be accomplished either by reductive reactions or by oxidative reactions. In general, reductive reactions led to cleavage of azo dyes into aromatic amines, which are further mineralized by yeasts. Enzymes putatively involved in this process are NADH-dependent reductases [24] and an azoreductase [16], which is dependent on the extracellular activity of a component of the plasma membrane redox system, identified as a ferric reductase [19]. Recently, significant increase in the activities of NADH-dependent reductase and azoreductase was observed in the cells of Trichosporon beigelii obtained at the end of the decolorization process [25]. 

Also ascomycetes yeast strains showed decolorizing behaviors due to extracellular reactions on polar dyes. The process occur when an alternative carbon and energy source is available. The involvement of an externally directed plasma membrane redox system was suggested in S. cerevisiae, the plasma membrane ferric reductase system participates in the extracellular reduction of azo dyes [25]. 

Recent development of mitochondrial theory of aging is so-called reductive hotspot hypothesis. De Grey [465] proposed that the cells with suppressed oxidative phosphorylation survive by reducing dioxygen at the plasma membrane rather than at the mitochondrial inner membrane. Plasma membrane redox system is apparently an origin of the conversion of superoxide into hydroxyl and peroxyl radicals and LDL oxidation. Morre et al. [466] suggested that plasma membrane oxidoreductase links the accumulation of lesions in mitochondrial DNA to the formation of reactive oxygen species on the cell surface. 

Asard. H.. A. Bcnczi. and R.J. Caubcrgs Plasma Membrane Redox Systems and Their Rale in Biological Stress and Disease. Kluwcr Academic Publishers. Noiwelt. MA. 1999. 

Villalba JM and Navas P (2000) Plasma membrane redox system in the control of stress-induced apoptosis. Antioxidants and Redox Signaling 2,213-30. 

Observational studies In a comparison of HBOC-201 and erythrocyte transfusion, the former caused mild platelet dysfunction, which may be caused by reactive oxygen molecules. In blood, there is redox hemostasis as a result of a trans-plasma membrane redox system in platelets. This hemostasis could be impaired by free radicals [23 ]. 

It is clear that ferric chelates present in soil water are the natural electron acceptors for the inducible system (or turbo reductase) responsible for ferric reduction prior to iron uptake by dicotyledoneous and nongrass monocotyledoneous plants (Holden et al., 1991 Lesuisse and Labbe, 1992). In contrast, the natural electron acceptor of the so-called constitutive plasma membrane redox system both in plant and animal cells has not been completely defined. In addition to oxygen and iron-containing compounds, the semioxidized form of ascorbate, AFR, has been proposed as a natural electron acceptor (Goldenberg et al, 1983). 

Medina, M. A., and Schweigerer, L., 1993, A plasma membrane redox system in human retinoblastoma cells, Biochem. Mol. Biol. Int. 29 881-887. 

Misra, P. C., Craig, T, and Crane, F. L., 1984, A link between transport and plasma membrane redox systems in carrot cells, J. Bioenerg. Biomembr. 16 143-152. 

Figure 3. Chemicals reduced by fungal plasma membrane redox system.

Valli et al. (88) suggested that intracellular nitroreductases may be involved in 2,4-DNT reduction by R chrysosporium. Even though intracellular nitroreductases of R chrysosporium probably exist, there is no current evidence that supports their involvement in TNT reduction. Conversely, there are a number of experiments which suggest that TNT is reduced by a plasma membrane redox system in R chrysosporium (81). TNT reduction requires live, intact mycelia. Any condition that disrupts the integrity of the plasma membranes (freeze-thawing or grinding) destroys the reduction activity. Also, no significant reduction is observed with either supplemented (NADPH, NADH, or ATP) or unsupplemented extracellular or intracellular fractions of the culture, under aerobic or anaerobic conditions (81). 

Low, H., F. L. Crane, E. J. Partick, G. S. Patten, and M. G. Clark. 1984. Properties and regulation of a trans-plasma membrane redox system of perfused rat heart. Biochim. Biophys. Acta 804 253-260. 

Plasma membranes of all cells investigated so far contain an electron transport system transferring electrons from NADH to an extracellular electron acceptor (for review, see Navas et al., 1994 and Chapter 4 of this volume). Electron transport across the plasma membrane is accompanied by release of protons from the cell, presumably due to an activation of the Na+/H+ antiport (Sun et a/., 1988). Since proton release and the concomitant increase in cytoplasmic pH have been connected to growth stimulation (Moolenar et al., 1983), it was proposed that the transplasma membrane redox system via proton release might also be involved in the regulation of proliferation. 

To reach the reductive step of the azo bond cleavage, due to the reaction between reduced electron carriers (flavins or hydroquinones) and azo dyes, either the reduced electron carrier or the azo compound should pass the cell plasma membrane barrier. Highly polar azo dyes, such as sulfonated compounds, cannot pass the plasma membrane barrier, as sulfonic acid substitution of the azo dye structure apparently blocks effective dye permeation [28], The removal of the block to the dye permeation by treatment with toluene of Bacillus cereus cells induced a significant increase of the uptake of sulfonated azo dyes and of their reduction rate [29]. Moreover, cell extracts usually show to be more active in anaerobic reduction of azo dyes than whole cells. Therefore, intracellular reductases activities are not the best way to reach sulfonated azo dyes reduction the biological systems in which the transport of redox mediators or of azo dye through the plasma membrane is not required are preferable to achieve their degradation [13]. 

In 1986, the antioxidant effects of thioredoxin reductase were studied by Schallreuter et al. [81]. It has been shown that thioredoxin reductase was contained in the plasma membrane surface of human keratinocytes where it provided skin protection against free radical mediated damage. Later on, the reductive activity of Trx/thioredoxin reductase system has been shown for the reduction of ascorbyl radical to ascorbate [82], the redox regulation of NFkB factor [83], and in the regulation of nitric oxide-nitric oxide synthase activities [84,85],... 

Over the years, there have been numerous reports of oxidase preparations that contain polypeptide components, additional to those described above. As yet no molecular probes are available for these, and so their true association with the oxidase is unconfirmed. There are many reports in the literature describing the role of ubiquinone as an electron transfer component of the oxidase, but its involvement is controversial. Quinones (ubiquinone-10) have reportedly been detected in some neutrophil membrane preparations, but other reports have shown that neither plasma membranes, specific granules nor most oxidase preparations contain appreciable amounts of quinone, although some is found in either tertiary granules or mitochondria. Still other reports suggest that ubiquinone, flavoprotein and cytochrome b are present in active oxidase preparations. Thus, the role of ubiquinone and other quinones in oxidase activity is in doubt, but the available evidence weighs against their involvement. Indeed, the refinement of the cell-free activation system described above obviates the requirement for any other redox carriers for oxidase function. 

The plasma membranes of plant cells possess several redox activities that can be related to both plant nutrition and cell wall formation and lignification (Liithje et al., 1997 Berczi and Mpller, 2000). In this context, it has been shown that in oat roots, HMS humic fractions inhibited NADH oxidation in either the presence or absence of an artificial electron acceptor (ferricyanide), whereas LMS fractions inhibited this oxidase only if the electron donor (NADH) and acceptor (ferricyanide) were added at the same time (Pinton et al., 1995). While the first effect could be related to the activity of surface peroxidases that can be involved in cell wall formation and thickening (Vianello and Macri, 1991), the second seems to be exerted on a different redox system with an unknown function (Nardi et al., 2002). 

The redox system does not depend on endosomal acidification but needs TfR. Fe2Tf first binds to TfR which is located in close proximity to the proton-and electron-pumping NADHiTf oxidoreductase. The Fe—Tf bond is destabilized by proton efflux, making Fe3+ susceptible to reduction. Fe2+ is trapped by a plasma membrane binder and can be transported by a translocator [4]. As Al is a simple trivalent cation incapable of redox changes, it may be theoretically impossible that Al bound to Tf is taken up by a redox mechanism. Actually, no reports on a redox-mediated process of Al bound to Tf have been made. 

If both MT-1 and HO-1 mRNA induction by heme-hemopexin involves a copper-redox enzyme in both heme transport (and consequent induction of HO-1 mRNA) and the signaling pathway for MT-1 expression, a plausible working model can be formulated by analogy with aspects of the yeast iron uptake processes and with redox reactions in transport (Figure 5-6). First, the ferric heme-iron bound to hemopexin can act as an electron acceptor, and reduction is proposed to be required for heme release. The ferrous heme and oxygen are substrates for an oxidase, possibly NADH-dependent, in the system for heme transport. Like ferrous iron, ferrous heme is more water soluble than ferric heme and thus more suitable as a transport intermediate between the heme-binding site on hemopexin and the next protein in the overall uptake process. The hemopexin system would also include a copper-redox protein in which the copper electrons would be available to produce Cu(I), either as the copper oxidase or for Cu(I) transport across the plasma membrane to cytosolic copper carrier proteins for incorporation into copper-requiring proteins [145]. The copper requirement for iron transport in yeast is detectable only under low levels of extracellular copper as occur in the serum-free experimental conditions often used. 

Rieske protain/centar an iron-sulphur protein first isolat from Complex III of the mitochondrial electron transport chain, in which it occurs with cytochromes b and C) [J.S, Rieske el al. Biochem. Biophys Res Commun. IS (1%4) 338-344], but which has now been found in the equivalent cytochrome be complexes in the bacterial plasma membrane and the chloroplast thylakoid membrane. The latter, known as the cytochrome bff complex, partidpates in cyclic and noncyclic electron flow in the light phase of photosynthesis (see Photosynthesis). All Rieske proteins are one-electron redox systems with a standanl redox potential in the + 0.2 to + 0.3V range and have a (2Fe-2S] center, a single membrane-spanning a-helix, and a characteristic electron spin resonance (ESR) spectrum. The chloroplastidic R.p/c, with a M, of - 20,000, is smaller than that of the mitochondnon. It is encoded in the nucleus, synthesized in the cytoplasm and translocated to the chloroplast, where it is inserted into the thylakoid membrane. Within the thylakoid membrane its [2Fe-2S] redox centre (near to its C-terminus) can readily pass electrons to cytochrome /, a c-type cytochrome that projects from the luminal surface cytochrome / then passes electrons to plastocyanin (see) dissolved in the aqueous milieu of the thylakoid lumen. 

Redox reactions are essential for the function of cell membranes (Del Castillo-Olivares et al. 2000). It should be stressed that every bioenergetic-ally competent cell membrane does contain redox systems (Skulackev 1988). A plasma membrane electron transport or redox system has been found in every living cell tested. Voegtlin et al. (1925) examined a relation between the redox state and cancer. The redox potential of cytochrome bsss.. a component of NADPH oxidase, is -245 mV. This is atypically low for a cytochrome b, but this fact enables the reduction of oxygen to snperoxide (Cross... 

The eukaryotic plasma membrane contains a redox system that transfers electrons from intracellular donors to impermeable external oxidants. This redox activity has been related to growth control and development (Crane et al., 1985). Although there is general agreement on NAD(P)H as the natural electron donor (Navas and Buron, 1990), the identification of natural electron acceptors for the transmembrane dehydrogenase is still a matter of controversy. 

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