Archaebacteria

Relatively little is known about this group of procaryotes, and from an industrial viewpoint the main interest in them is that they contain a group, known as the methanogens, which is able to form methane from carbon dioxide and acetic acid. 

They can be divided into several groups, most of which are very difficult to grow and are generally considered to be so different to the Eubacteria that most authors place them in a separate kingdom. 

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Syntheses of Archaebacteria 36- and 72-member macrocyclic membrane lipids (di- and tetraethers) 99YGK785. 

During the 1960s, research on proteins containing iron—sulfur clusters was closely related to the field of photosynthesis. Whereas the first ferredoxin, a 2[4Fe-4S] protein, was obtained in 1962 from the nonphotosynthetic bacterium Clostridium pasteurianum (1), in the same year, a plant-type [2Fe-2S] ferredoxin was isolated from spinach chloroplasts (2). Despite the fact that members of this latter class of protein have been reported for eubacteria and even archaebacteria (for a review, see Ref. (3)), the name plant-type ferredoxin is often used to denote this family of iron—sulfur proteins. The two decades... 

The 2[4Fe-4S] and [3Fe-4S][4Fe-4S] ferredoxins are components of virtually all eubacteria and archaebacteria (3). Several comprehensive reviews dealing with these small metalloproteins have appeared (3, 8-12), but only those participating directly in the photosynthetic light reactions will be addressed here. 

The double bonds were reduced to the give the saturated compounds, so the doublebond configuration was not an immediate issue. It appears, however, that the -double bonds are formed. The debenzylated derivatives of propan-1,2,3-triol occur as lipid components in various prokaryotes (archaebacteria) that grow under extreme thermal conditions. 

Archaea or Archaebacteria, which live in sulphurous waters around undersea volcanic vents. An extraordinarily stable enzyme which functions even at 135 °C and survives at pH 3.2-12.7 has been identified [142]. This enzyme has been termed STABLE (stalk-associated archaebacterial endoprotease). It is suggested that such exceptional stability may be attributable to unusually large Mr and tight folding of the protein chain. Suggested uses include washing powders and detergents, as well as industrial catalysts. It is even proposed that such remarkable properties may have contributed to the early evolution of life on earth [142]. 

Most of the bacterial viruses which have been studied in any detail infect bacteria of the enteric group, such as Escherichia coli and Salmonella typhimurium. However, viruses are known that infect a variety of procaryotes, both eubacteria and archaebacteria. A few bacterial viruses have lipid envelopes but most do not. However,... 

A second example of the differences between important biomolecules in archaebacteria and eubacteria is their DNA-dependent RNA polymerase. The enzyme found in archaea resembles that in eukaryotes more than it does those in bacteria ... 

Woese chose the name archaebacteria because these microorganisms grow best under conditions which were probably found on the primeval Earth between 3.5 and 4 billion years ago hot boiling water and thermal vents, highly acidic environment, oxygen-free atmosphere and high salt concentrations. 

In normal human subjects, some 25 % of total body iron (800-1000 mg) is present in the storage forms, mostly as ferritin. Whereas it is likely that all mammalian cell types contain some ferritin, haemosiderin in normal subjects is essentially restricted to cells of the reticuloendothelial system. Ferritin turns out to be almost universal in its distribution ferritin and ferritin-like proteins have been found in all organisms except for one or two archaebacteria. In contrast, haemosiderin has not been found to any extent outside of iron-loaded animals, except for a brief report of a phytosiderin in pea seeds (Laulhere et ah, 1989). 

Mainly in archaebacteria the other coenzymes and cofactors occur in many organisms but not all synthesise them. 

Fig. 5.7. In green sulfur bacteria and in some archaebacteria, a reverse citric acid cycle is used for the assimilation of C02. It must be assumed that this was the original function of the citric acid cycle that only secondarily took over the role as a dissimulatory and oxidative process for the degradation of organic matter. A major enzyme here is 2-oxoglutarate ferredoxin for C02 fixation. Note that it, like several other enzymes in the cycle, uses Fe/S proteins. One is the initial so-called complex I which has eight different Fe/S centres of different kinds but no haem (see also other early electron-transfer chains, e.g. in hydrogenases).

These microorganisms belong to the Archaebacteria and thus possess unique molecular... 

This may explain why this family of bacteria is found in dairy products where the presence of lactoferrin makes iron availability problematic. Class II RNRs is also found in some archaebacteria. 

Mn superoxide dismutases are found in both eubacteria and archaebacteria as well as in eukaryotes, where they are frequently found in mitochondria. They (Figure 16.1) have considerable structural homology to Fe SODs both are monomers of 200 amino acid and occur as dimers or tetramers, and their catalytic sites are also very similar. They both catalyse the two-step dismutation of superoxide anion and, like the Cu-Zn SODs, avoid the difficulty of overcoming electrostatic repulsion between two negatively charged superoxide anions by reacting with only one molecule at a time. As in the case of Cu-Zn SOD, a first molecule of superoxide reduces the oxidized (Mn3+) form of the enzyme, releasing... 

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