Ferric reductases

Figure 50-4. Absorption of iron. is converted to Fe + by ferric reductase, and Fe " is transported into the enterocyte by the apicai membrane iron transporter DMTl. Fieme is transported into the enterocyte by a separate heme transporter (HT), and heme oxidase (FiO) reieases Fe from the heme. Some of the intraceiiuiar Fe + is converted to Fe + and bound by ferritin. The remainder binds to the basoiaterai Fe + transporter (FP) and is transported into the biood-stream, aided by hephaestin (FiP). in piasma, Fe + is bound to the iron transport protein transferrin (TF). (Reproduced, with permission, from Ganong WF Review of Medical Physiology, 21 st ed. McGraw-Hill, 2003.)...

Vadas A, HG Monbouquette, E Johnson, I Schroder (1999) Identification and characterization of a novel ferric reductase from the hyperthermophilic archaeon Archaeoglobus fulgidus. J Biol Chem 274 36715-36721. 

As we saw in the previous section, Strategy 1 plants utilize ferric reductases, with NADPH as electron donor, coupled to proton extrusion and a specific Fe(II) transport system localized in the root plasma membrane. Saccharomyces cerevisiae also uses cell surface reductases to reduce ferric iron, and in early studies (Lesuisse et ah, 1987 ... 

Figure 8.3 A model of iron transport across the intestine. Reduction of ferric complexes to the ferrous form is achieved by the action of the brush border ferric reductase. The ferrous form is transported across the brush border membrane by the proton-coupled divalent cation transporter (DCT1) where it enters an unknown compartment in the cytosol. Ferrous iron is then transported across the basolateral membrane by IREG1, where the membrane-bound copper oxidase hephaestin (Hp) promotes release and binding of Fe3+ to circulating apotransferrin. Except for hephaestin the number of transmembrane domains for each protein is not shown in full. Reprinted from McKie et al., 2000. Copyright (2000), with permission from Elsevier Science.

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]. 

Ramalho PA, Paiva S, Cavaco-Paulo A et al (2005) Azo reductase activity of intact Saccharomyces cerevisiae cells is dependent on the Frelp component of plasma membrane ferric reductase. Appl Environ Microbiol 71 3882-3888... 

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]. 

Myers CR, Myers JM (1993) Ferric reductase is associated with the membranes of anaerobically grown Shewanellaputrefaciens MR-1. FEMS Microbio Lett 108 15-22 Myers CR, Nealson KH (1988) Bacterial manganese reduction and growth with manganese oxide as the sole electron acceptor. Science 240 1319-1321... 

However, near-stoichiometric Fe " ion binding to NifU-1 or NifU was observable only in experiments conducted at 2°C in anaerobic samples that had been pretreated with dithiothreitol to ensure reduction of any intrasubunit or intersubunit disulfides. At room temperature, <10% of the NifU-1 or NifU was in a Fe bound form, and colorimetric analysis indicates that the remainder of the Fe is in solution was in the form of free Fe " ion. Hence this mononuclear Fe -bound species is more likely to be an intermediate in the reduction of Fe ion by NifU or NifU-1 rather than an initial step in cluster assembly on the NifU-1 domain of NifU. In this connection, it is important to note that Fe is rapidly reduced to Fe by cysteine in aqueous solution (Schubert, 1932). The physiological significance (if any) of the apparent ferric reductase activity associated with the NifU-1 domain of NifU remains to be established. 

Toole-Simms, W. (1988). Regulation of proton release from HeLa cells by ferric reductase. Ph.D. Thesis, 160 pp., Purdue University, West Lafayette, IN. 

Iron levels are tightly regulated through control of dietary absorption of iron. The duodenum and upper jejunum are the only areas of the body where this occurs. Since nonheme iron forms insoluble complexes when ingested, it must first be converted into soluble complexes. This is accomplished on the apical surface of duodenal villus enterocytes by duodenal ferric reductase, which converts insoluble duodenal ferric (Fe3+) iron into soluble and absorbable ferrous (Fe2+) iron. Iron is then transported across the membrane to the cytoplasm through a transporter known as the divalent metal transporter 1 (DMT-l), a proton sym-porter (Harrison and Bacon, 2003). 

Dancis, A., Klausner, R. D., Hinnebusch, A. G., and Barriocanal, J. G. (1990). Genetic evidence that ferric reductase is required for iron uptake in Saccharomyces cerevisiae. Mol. Cell. Biol. 10, 2294-2301. 

Intestinal absorption of dietary iron. Ferrous iron is absorbed by the duodenal villus tip enterocytes mediated by divalent metal transporter-1 (DMTI). Iron transport mediated by DMTl of the apical surface and the basolateral tran.sporter at the basolateral surface are coupled to ferric reductase and ferroxidase that change the iron oxidation state, respectively. The degree of iron entry is determined by the level of DMTl and its level of expression is programmed in the crypt cells. The programming of the crypt cells is coupled to the body iron stores via transferrin-mediated and HFE protein-modulated iron transport. [Modified and reprinted with permission from B. R. Bacon, L. W. Powell,... 

McKie a, Baeeow D, Iatunde-Dada GO, Roles A, Sayee G, Mudaly F, Mudaly M, Richaedson C, Baeeow D, Bomeoed A, Petees TJ, Raja K, Shiealis, Hedigee MA, Faezaneh F and Simpson RJ (2001) An iron-regulated ferric reductase associated with the absorption of dietary iron. Science 291 1755-1759. 

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