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Photosynthesis purple nonsulfur

Many phototrophs do not produce O2 as a waste product. Such anoxygenic phototrophs are comprised of purple sulfur, purple nonsulfur, green sulfur, and green nonsulfur bacteria. Although purple sulfur bacteria are typically found in anoxic zones of lakes and sediments, many are capable of photosynthesis under oxic conditions (Van Gemer-den, 1993). Most fix N2 and store S° intra- or extracellularly, and some are capable of chemo-lithoautotrophic growth. Extreme halophilic, sulfi-dic, and mildly thermophilic environments harbor... [Pg.4187]

Figure 30 summarizes the main proposals for cytochrome c involvement in Chromatium photosynthesis (377-380). Cytochromes C662 and Cess are the components of the cytochrome complex listed in Table XX. There are obvious analogies with green plant and purple nonsulfur bacterial photosynthesis (Figs. 27 and 29), but with less known about intermediate substances. It has been proposed that the high potential Ciu participates in cyclic photosynthesis and the lower potential cs52 is involved mainly in substrate-fed noncyclic photosynthesis, but this distinction is muddied because there is some communication between the two cytochromes... [Pg.513]

This is a remarkable state of affairs. We tend to think of photosynthesis and respiration as having had a long independent history, yet in regions of shared structure, respiratory c from mammals and respiratory C560 from Micrococcus are no different from the photosynthetic Cg of purple nonsulfur bacteria than the individual Ca s are among themselves. Part of our impression that man and Micrococcus are farther apart than R. capsulata and R. spheroides may lie in the eye of the beholder, but we would have expected more distinction between Ca and the other proteins than is observed. [Pg.541]

It could be that the break between respiration and photosynthesis in these bacteria is more recent than we think. Cytochrome Ca has been suggested to have a respiratory as well as a photosynthetic role in R. spheroides (S72) and R. capsulata (372a-c) and no alternative respiratory chain has yet been identified in any of the Athiorhodaceae. In some of these organisms a situation may exist as in Fig. 46 with electrons flowing to both from light-excited bacteriochlorophyll and from external donors, and then from c either to an electron-depleted bacteriochlorophyll or to an oxidase molecule. This would account for the observed control mechanism in the purple nonsulfur bacteria. Under aerobic conditions in the dark, bacteriochlorophyll would not be electron-defi.cient, whereas the oxidase would be in its oxidized state and capable of accepting electrons from c. Under anaerobic conditions, electrons would reduce the oxidase, and further electron transfer down that path would be blocked. Light then would promote electrons away from bacteriochlorophyll and set cyclic photophosphorylation in motion. [Pg.541]

Anoxic photosynthesis utilizes light energy, but does not produce oxygen. Green and purple bacteria of the sulfur and nonsulfur kind are anoxic photosynthesizers. The sulfur bacteria oxidize sulfide to elemental sulfur and can even oxidize it further to sulfate. [Pg.220]


See other pages where Photosynthesis purple nonsulfur is mentioned: [Pg.3896]    [Pg.4187]    [Pg.4252]    [Pg.449]    [Pg.505]    [Pg.510]    [Pg.510]    [Pg.513]    [Pg.545]    [Pg.562]    [Pg.818]    [Pg.3896]    [Pg.3897]    [Pg.3970]    [Pg.560]    [Pg.237]    [Pg.93]    [Pg.93]   
See also in sourсe #XX -- [ Pg.510 , Pg.511 ]




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