Prokaryotes from photosynthetic

Several methylated sugars have been identified in hydrolyzates of LPS, cell-wall polysaccharides, and extracellular polysaccharides. A considerable number of these have been found in the LPS from photosynthetic prokaryotes. Two polysaccharides from Mycobacterium species, a glucan" and a mannan" are remarkable in that they contain high percentages of methylated sugars. Glycolipids from Mycobacterium species are also rich in methylated sugars, some of which have not been found elsewhere, but this is beyond the scope of the present article. 

Figure 12. Possible evolutionary interrelationships of aerobic prokaryotes evolving from photosynthetic bocateria (24).

Polymers of fructose are of widespread occurrence in plants, but are common only in a few orders, particularly the Compositae ind Graminae, They differ in several respects from prokaryotic fructans, especially in that they are intracellular rather than extracellular, that they are far smaller than their bacterial counterparts and that they contain relatively more glucose. Their function in plants is as storage polysaccharides and they are synthesised, ultimately from photosynthetic products. In bacteria such polymers are often assembled from exogenous, rather than endogenous disaccharides. 

Photosystem I reaction center, that functions on the reducing side of the electron transport chain, may have evolved from green photosynthetic bacteria (Olson 1970). Cyanobacteria which are the only free-living prokaryotes containing photosynthetic systems of the higher plants type, played a central role in the evolution of the complex (Padan 1979). 

Electron Transport Between Photosystem I and Photosystem II Inhibitors. The interaction between PSI and PSII reaction centers (Fig. 1) depends on the thermodynamically favored transfer of electrons from low redox potential carriers to carriers of higher redox potential. This process serves to communicate reducing equivalents between the two photosystem complexes. Photosynthetic and respiratory membranes of both eukaryotes and prokaryotes contain stmctures that serve to oxidize low potential quinols while reducing high potential metaHoproteins (40). In plant thylakoid membranes, this complex is usually referred to as the cytochrome b /f complex, or plastoquinolplastocyanin oxidoreductase, which oxidizes plastoquinol reduced in PSII and reduces plastocyanin oxidized in PSI (25,41). Some diphenyl ethers, eg, 2,4-dinitrophenyl 2 -iodo-3 -methyl-4 -nitro-6 -isopropylphenyl ether [69311-70-2] (DNP-INT), and the quinone analogues,... 

Prokaryotic cells have only a single membrane, the plasma membrane or cell membrane. Because they have no other membranes, prokaryotic cells contain no nucleus or organelles. Nevertheless, they possess a distinct nuclear area where a single circular chromosome is localized, and some have an internal membranous structure called a mesosome that is derived from and continuous with the cell membrane. Reactions of cellular respiration are localized on these membranes. In photosynthetic prokaryotes such as the cyanobacteria,... 

The oxidation of carotenes results in the formation of a diverse array of xanthophylls (Fig. 13.7). Zeaxanthin is synthesised from P-carotene by the hydroxylation of C-3 and C-3 of the P-rings via the mono-hydroxylated intermediate P-cryptoxanthin, a process requiring molecular oxygen in a mixed-function oxidase reaction. The gene encoding P-carotene hydroxylase (crtZ) has been cloned from a number of non-photosynthetic prokaryotes (reviewed by Armstrong, 1994) and from Arabidopsis (Sun et al, 1996). Zeaxanthin is converted to violaxanthin by zeaxanthin epoxidase which epoxidises both P-rings of zeaxanthin at the 5,6 positions (Fig. 13.7). The... 

Genes encoding glucose transporters have recently been cloned from three photosynthetic organisms, the prokaryotic cyanobacterium Synechocystis [208,209], the... 

The distribution of elements in single-cell non-photosynthetic eukaryotes is probably best seen in terms of the well-defined compartments of yeast. The central cytoplasmic compartment containing the nucleus has many free element concentrations, only somewhat different from those in all known aerobic prokaryotes (Figure 7.7). (The nuclear membrane is a poor barrier to small molecules and ions and so we include the nucleus with the cytoplasm.) We do not believe in fact that the free cytoplasmic values of Mg2+, Mn2+, Fe2+, Ca2+, and possibly Zn2+, have changed greatly throughout evolution. As stressed already there are limitations since free Mg2+ and Fe2+ are essential for the maintenance of the primary synthetic routes of all cells, and changes in other free metal ions could well have imposed... 

Plastocyanins are the most widely studied cupredoxins. They are one of the most abundant copper proteins in plant photosynthetic tissues. Plant plastocyanins have an intricate evolutionary history because of their ancient bacterial origin. It is currently well accepted that plants diverged from the main eukaryotic domain into a separate lineage when the unicellular, oxygen respiring common ancestor of the eukaryotes incorporated a prokaryotic endosymbiont, the cyanobacterial chloroplast. 

Recent advances in understanding the phylogeny of photosynthetic prokaryotes have been made by comparing oligonucleotides derived from 16S rRNA [1]. Results of these analyses have renewed general interest in the comparative biochemistry of photosynthetic bacteria, since it is now clear that they are closely related to many non-photosynthetic bacteria. Extensive phylogenetic analysis has indicated that the ancestry of most, if not all, eubacteria and even the ancestry of the cellular organelles of eukaryotes, the mitochondria and chloroplasts, lies deeply entrenched in the history of the photosynthetic bacteria. 

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