Cell walls of bacteria

FIGURE 2.16 pH versus enzymatic activity. The activity of enzymes is very sensitive to pH. The pH optimum of an enzyme is one of its most important characteristics. Pepsin is a protein-digesting enzyme active in the gastric fluid. Trypsin is also a proteolytic enzyme, but it acts in the more alkaline milieu of the small intestine. Lysozyme digests the cell walls of bacteria it is found in tears. 

FIGURE 11.22 If the cell walls of bacteria such as Escherichia coli are partially digested and the cells are then osmotlcally shocked by dilution with water, the contents of the cells are extruded to the exterior. In electron micrographs, the most obvious extruded component is the bacterial chromosome, shown here surrounding the cell. (Dr. Gopal Murti/CNRI/Phototakr NYC)... 

FIGURE 1119 The lysozyme molecule is a typical enzyme molecule. Lysozyme is present in a number of places in the body, including tears and the mucus in the nose. One of its functions is to attack the cell walls of bacteria and destroy them. This "ribbon" representation shows only the general arrangement of the atoms to emphasize the overall shape of the molecule the ribbon actually consists of amino acids linked together (Section 19.13). 

B. Hexoses.—Muramic acid 6-phosphate (63), which occurs in the cell walls of bacteria, has now been synthesised, thus confirming the structure of this acid-stable compound. 

The Florey-Chain team s investigation showed that penicillin interferes with the cell wall of bacteria. Bacteria cells ruptured instead of continuing to grow. In 1938, their animal test, on eight mice given lethal doses of infectious bacteria, showed stunning results. The four mice with penicillin survived, whereas four controls with no medication died. Their first human patient who suffered from infection showed early improvement with penicillin, but died subsequently when the stock of penicillin was exhausted. 

Indeed, these results are qualitatively similar to those depicted in Figs. 12 and 13, and it is therefore tempting to ascribe them to the presence, on the bacterial cell walk, of polyanionic environments surrounding the sites where lysozyme cleaves the polysaccharide network. However, the point is that, although several authors have concluded from various experimental observations that the cell walls of bacteria such as Escherichia coli and Micrococcus luteus are predominantly negatively charged (Katerakky et al, 1953 Salton, 1964 Davies et al, 1969), the complexity of the bacterial cell wall architecture means that little is known about the... 

Here is an important point almost all chiral amino acids that occur naturally in proteins throughout all of nature have L-stereochemistry. Why has nature uniquely selected L-amino acids for the construction of proteins No one knows for sure. In passing, we note that D-amino acids do occur in some living systems. The cell walls of bacteria possess both d- and L-amino acids, for example. However, these are introduced in a manner distinct from that employed to synthesize proteins. 

Fluoro amino acids have been incorporated into peptides, in order to ease the transport or reduce the systemic toxicity. Thus, trifluoroalanine, a powerful inhibitor of alanine racemase, is an essential enzyme for the biosynthesis of the cell wall of bacteria. It has a low antibiotic activity because of its very poor transport. In order to facilitate this transport, the amino acid has been incorporated into a peptide. This delivery allows a reduction of the doses, and thus the toxicity of the treatment is lowered.3-FIuorophenylaIanine (3-F-Phe) is a substrate of phenylalanine hydroxylase, which transforms it into 3-F-Tyr. 3-F-Tyr has a high toxicity for animals, due to its ultimate metabolization into fluorocitrate, a powerful inhibitor of the Krebs cycle (cf. Chapter 7). 3-F-Phe has a low toxicicity toward fungus cells, but when delivered as a tripeptide 3-F-Phe becomes an efficient inhibitor of the growth of Candida albicans. This tripeptide goes into the cell by means of the active transport system of peptides, where the peptidases set free the 3-F-Phe. ... 

Carbohydrates are the most abundant biomolecules on Earth. Each year, photosynthesis converts more than 100 billion metric tons of C02 and H20 into cellulose and other plant products. Certain carbohydrates (sugar and starch) are a dietary staple in most parts of the world, and the oxidation of carbohydrates is the central energy-yielding pathway in most nonphotosynthetic cells. Insoluble carbohydrate polymers serve as structural and protective elements in the cell walls of bacteria and plants and in the connective tissues of animals. Other carbohydrate polymers lubricate skeletal joints and participate in recognition and adhesion between cells. More complex carbohydrate polymers covalently... 

Polysaccharide chains in the peptidoglycan layer (Fig. 8-29) of the cell walls of bacteria are attacked and cleaved by lysozymes,55 enzymes that occur in tears and other body secretions and in large amounts in egg white. Some bacteria and fungi, and even viruses, contain lysozymes.56 Their function is usually to protect against bacteria, but lysozyme of phage T4 is a component of the baseplate of the virus tail (Box 7-C). 

Sugar amino acids (Saa) 1 are carbohydrate scaffolds that carry an amino and a carboxy function.12 Due to their structural and functional diversity, no detailed nomenclature for this class of amino acids has yet been established. Saa are found in nature as subunits of oligosaccharides (neuraminic acid 1) in cell walls of bacteria (muraminic acid 2) and in some antibiotics 3-6 (Scheme l). 2-8 ... 

The polysaccharides which will be considered in this paper are all found in the extracellular capsular material which surrounds the cell wall of bacteria belonging to the Genus Klebsiella. The carbohydrate nature of these capsules was first demonstrated in 1914 by Toenniessen (J ) and in 1926 Julianelle (2) was the first person to report on the presence of sharply defined and high specific types of polysaccharides in the different serotypes. 

Silver LL (2005) Does the cell wall of bacteria remain a viable source of targets for novel antibiotics. Biochem Pharmacol 71 996-1005... 

Figure 4.2 A lysozyme protects against bacterial infection by destroying the cell walls of bacteria. The above image shows the protein (blue) and backbone (magenta) of a lysozyme. It also shows the substrate (yellow) which is bound to the active site.

Hopanes organic molecules found in the cell walls of bacteria. 

This particular mycoside Ci preparation contains three different deoxy-hexoses 6-deoxytalose, 6-deoxy-3-0-methyltalose, and 3,4-di-O-methyl-rhamnose. The peptide portion of this mycoside C contains three different amino acids linked in a pentapeptide. One molecular proportion contains one molecule of u-phenylalanine, two molecules of D-o/Io-threonine, atid two molecules of D-alanine the pentapeptide has the structure D-Phc-D-allo-Thr-D-Ala-D-oZZo-Thr-D-Ala. The unnatural configuration of all of the constituent amino acids and the presence of D-oWo-thrconine arc remarkable features. It may be recalled that D-amino acids have also been found in the peptide portion of wax D (see page 220) and arc usually found in the cell walls of bacteria. 

Glycoproteins will be discussed in some detail in Section 12.4. The carbohydrate components of proteoglycans are known as glycosaminoglycans. Proteoglycans are essential parts of the connective tissue In mammals and are also present to some extent in fish and bacteria (peptidoglycans from the cell wall of bacteria are different biopolymers and were discussed in Section 7.9). The term mucopolysaccharide was used in the past to describe polysaccharide materials of animal origin containing 2-amino-2-deoxyhexoses. 

Penicillin weakens the cell wall of bacteria, rupturing and destroying the cell in a process called lysis. 

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