Prokaryotic groups

Within the NiFe(Se) hydrogenase family, the unrooted tree (Fig. 2.4) clearly reveals several major lineages. As might be expected, the enzyme groups discussed above all emerge as distinct clades which reflect the major prokaryotic groups and the enzyme... 

Blattner FR, Plunkett G III, Block CA, Perna NT, Burland V, Riley M et al (1997) The complete genome sequence of Escherichia coli K-12. Science 277 1453-1462 Boucher Y, Douady CJ, Papke RT, Walsh DA, Boudreau MER, Nesbo CL, Case RJ, Doolittle WF (2003) Lateral gene transfer and the origins of prokaryotic groups. Annu Rev Genet... 

The wish to discover eukaryotic features in prokaryotes and to emphasize the uniqueness of archaebacteria has often been misleading. For example, introns in prokaryotic tRNA genes, first detected in archaebacteria and considered to be an eukaryotic feature, have later been found in eubacteria as well [153-154] reverse gyrase, once considered to be a hallmark of archaebacteria, was later found in extremely thermophilic eubacteria. In fact, if one considers the present data on chromosome structure (see Fig. 1) and DNA topology (Table 2), archaebacteria resemble more closely the eubacteria than the eukaryotes. Additional similarities between the two prokaryote groups, which have not been reviewed here, are the presence of... 

Prokaryotes are the simplest life form. Their small genome size limits the number of genes that control metabolic activities. Over time, some prokaryotic groups became multicellular organisms for this reason. Prokaryotes then evolved to form complex bacterial communities where species benefit from one another. 

Initial studies of the other major prokaryotic group, the cyanobacteria gave conflicting results but a detailed comparative study of several species indicated the absence of pyridine nucleotide glutamate synthase from all the species examined (Neilson and Doudoroff, 1973). 

Microbes recently identified as organic pollutant biodegraders, but falling outside of the prokaryotic groupings typically isolated for... 

Although some catabolic pathways are widespread, there are some correlations between certain types of metabolism and the prokaryotic group catalyzing those reactions. This can he attributed to the compatibility between the cataboKc reactions and the core metabolic pathways that the cataboKc intermediates feed into. This is particularly well illustrated for chemical compounds which are composed of a single carbon atom or which are readily metabolized to C-1 fragments. 

Table 4.3. Functional types of Major Facilitator Superfamily (MFS) carriers and their relative occurrences in five different prokaryotic groups of organisms.

All these intermediates except for cytochrome c are membrane-associated (either in the mitochondrial inner membrane of eukaryotes or in the plasma membrane of prokaryotes). All three types of proteins involved in this chain— flavoproteins, cytochromes, and iron-sulfur proteins—possess electron-transferring prosthetic groups. 

Formate dehydrogenases are a diverse group of enzymes found in both prokaryotes and eukaryotes, capable of converting formate to CO2. Formate dehydrogenases from anaerobic microorganisms are, in most cases, Mo- or W- containing iron-sulfur proteins and additionally flavin or hemes. Selenium cysteine is a Mo- ligand. 

Figure 5.3 The deduced evolutionary tree for selected members of the transferrin superfamily, based on comparisons of structures and sequences. The tree combines the transferrins with a number of prokaryotic periplasmic transport proteins. From Bruns et al., 1997. Reproduced by permission of Nature Publishing Group.

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