Manganese electron acceptor

The reductase in Geobacter sulfurreducens is located in the outer membrane and a soluble Fe(III) reductase has been characterized from cells grown anaerobically with acetate as electron donor and Fe(III) citrate or fumarate as electron acceptor (Kaufmann and Lovley 2001). The enzyme contained Fe, acid-labile S, and FAD. An extracellular c-type cytochrome is distributed in the membranes, the periplasm, and the medium, and functions as a reductase for electron transfer to insoluble iron hydroxides, sulfur, or manganese dioxide (Seeliger et al. 1998). 

The 1,2-oxaborolide anion (Figure 1), an analog of furan, has been prepared by two different routes and sandwich complexes with ruthenium and manganese 136, 137 have been characterized.153 Comparison of IR stretching frequencies suggests that oxaborolide is a weaker electron donor and better electron acceptor than cyclopentadienyl. 

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... 

All measured profiles of sulfate reduction in sediments indicate that much sulfide production and, by inference, oxidation occurs in permanently anaerobic sediments (78, 73, 90,101). The two most likely electron acceptors for anaerobic sulfide oxidation are manganese and iron oxides. Burdige and Nealson (151) demonstrated rapid chemical as well as microbially catalyzed oxidation of sulfide by crystalline manganese oxide (8-Mn02), although elemental S was the inferred end product. Aller and Rude (146) documented microbial oxidation of sulfide to sulfate accompanied by reductive dissolution... 

Measured rates of sulfate reduction can be sustained only if rapid reoxidation of reduced S to sulfate occurs. A variety of mechanisms for oxidation of reduced S under aerobic and anaerobic conditions are known. Existing measurements of sulfide oxidation under aerobic conditions suggest that each known pathway is rapid enough to resupply the sulfate required for sulfate reduction if sulfate is the major end product of the oxidation (Table IV). Clearly, different pathways will be important in different lakes, depending on the depth of the anoxic zone and the availability of light. All measurements of sulfate reduction in intact cores point to the importance of anaerobic reoxidation of sulfide. Little is known about anaerobic oxidation of sulfide in fresh waters. There are no measurements of rates of different pathways, and it is not yet clear whether iron or manganese oxides are the primary electron acceptors. 

A number of studies of phthalocyanine and porphyrin complexes of manganese have been carried out and it is clear that both MnIn and MnlV complexes can be photoreduced in the presence of water or OH- and in the absence of an electron acceptor.309 313 These complexes can be produced from Mn11 or Mnm complexes in the presence of an electron acceptor e.g. quinones,314 and the reaction can be sensitized by, for example, zinc porphyrins in suitable model membrane environments.310... 

Fig. 6. Sites of inhibitory action of DCMU in photosynthetic electron transport chain. The abbreviations are as follows - Cyt f cytochrome f, Fd ferredoxin, Mn water-splitting complex (manganese-containing), P680 pigment complex of photosystem II, P700 pigment complex of photosystem I, PC plastocyanin, PQ plastquinone, Q quencher, Rd NADP reductase and X direct electron acceptor complex...

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