Peptidoglycans peptide components

The resistance of Bacillus cereus cell-wall peptidoglycan to lysozyme action200 is due to the majority of the 2-amino-2-deoxy-D-glucosyl residues having free (nonsubstituted) amino groups. Polysaccharide and peptide components of the cell walls were converted into material susceptible to lysozyme by N-acetylation with acetic anhydride. 

Peptidoglycans are components of bacterial cell walls and consist of heteropolysaccharide chains cross-linked by short peptide chains. These cell walls bear the antigenic determinants when exposed to them, humans (and other mammalian species) develop specific antibodies to defend against bacteria. Bacterial virulence is also related to substances associated with the cell wall. Cell wall synthesis is the target for the action of the penicillins and cephalosporins. 

The main component of bacterial cell membranes is a mixed polymer known as murein or peptidoglycan. Peptidoglycan is a long polysaccharide chain that is cross-linked with short peptides. 

Peptidoglycans (14,16) are the primary component of bacterial cell walls. They consist of a heteropolysaccharide called murein cross-linked with short peptide chains. 

Most biologically active natural peptides are linear, but bacitracin is a leading member of the so-called cyclic peptide type of antibiotics. The commercial material, extracted from Bacillus subtilis, is a mixture of several compounds in which bacitracin A predominates. It exerts its action by inhibiting peptidoglycan synthesis and membrane function. Bacitracin has been a useful antibiotic since the 1960s, but its systemic use results in a number of toxic side effects, including nephrotoxicity. One cannot be sure which components of the mixture are responsible for the toxicity, and separation of natural constituents is complex and difficult. For this reason, an efficient synthesis of bacitracin A would be useful. 

The humin components isolated in DMS0/H2S04 media contain macromolecular components, such as peptides, peptidoglycans, and possibly mucopolysaccharides (Simpson et al., 2007), and these would appear to be strongly sorbed to the soil inorganic colloids. Such species can therefore be considered to have importance in soil particle interactions. 

One potentiaUy powerful indicator of source and diagenetic state is the D/L-amino acid ratio within DOM. Although proteins in nature contain primarily the L-enantiomer of amino acids, certain compounds, many of bacterial origin, do contain D-amino acids. Proteins do not contain D-amino acids but peptidyl compounds such as peptidoglycan (a structural component of bacterial ceU waUs Osborn, 1969), peptide antibiotics (Bodanszky and Perlman, 1969) and peptide... 

The major component of bacterial ceU walls is a complex polysaccharide known as a peptidoglycan. The name tells us that this structure consists of sugar molecules (-glycan) and peptides (peptido- short polymers of amino acids). 

Bacitracin is a mixture of similar peptides produced by fermentation of the bacterium Bacillus subtilis. The A-type component predominates. Its mode of action is to inhibit both peptidoglycan biosynthesis at a late stage (probably at the dephosphorylation of the phospholipid carrier step) and disruptions of plasma membrane function. It is predominantly active against Gram-positive microorganisms, and parenteral use is limited to IM injection for infants with pneumonia and empyema caused by staphylococci resistant to other agents. It is rather neuro- and nephrotoxic and, therefore, is used in this manner with caution. Bacitracin also is widely employed topically to prevent infection in minor cuts, scrapes, and burns. 

Occurrence The meso-form and occasionally its chiral isomers occur in the peptidoglycans of algal and bacterial cell walls. The meso-form is, in peptide-bound form, also a component of bacterial spores. The content amounts to 0.02 to 2.0% of the dry weight of the bacteria. D. is widely distributed. 

Penicillins and cephalosporins specifically inhibit late stages of the enzymatic construction of the bacterial peptidoglycan cell wall component, a network of peptides and polysaccharides. Since mammalian cells do not possess such a cell wall, the jS-lactam antibiotics are very specific and virtually non-toxic. This ideal property is not shared by other bactericidal substances, which impair or prevent growth of microorganisms by other, less specific, reaction mechanisms. This is true, e.g. for compounds affecting ion transport in lipid membranes. 

The mycobacterial cell wall contains three main components. Firstly, there is a skeleton composed of arabinogalactan mycolate covalently linked through a phosphodiester bond to peptidoglycan. There are also peptides which are removed by proteinolysis and free lipids which are easily extracted by solvents. 

---