CHEMISTRY OF CELL WALLS 



41 



comparison of the optical rotations of the synthetic and 

 naturally occurring compound suggests that the lactic acid 

 residue of the spore-peptide muramic acid possessed the 

 D-configuration. Zilliken ^^ has confirmed the synthesis of 

 muramic acid from D-glucosamine, using several modifica- 

 tions to the procedure developed by Strange and Kent.^^ 

 The structures proposed for muramic acid and that of the 

 muramic acid-nucleotide from Staphylococcus aureus ^^'^^ 

 suggest that the general function of muramic acid in the 

 cell wall is to link peptides (through an amide bond at the 

 carboxyl group of muramic acid) to other amino sugar or 

 sugar residues as shown below: 



^.^-'— CHo 



O H NHCOCH3 



CHoCHCONH 



Peptide 



Although Park ^* has shown that there is a 1:1 ratio of 

 muramic acid to D-glutamic acid in the walls of a number 

 of bacteria, it should not be assumed from the general type 

 of structure previously suggested that all or nearly all of the 

 muramic acid residues have peptide substituents. As is 

 shown in Chapter 3, in Micrococcus lysodeikticus walls 

 much of the muramic acid is unsubstituted. However, it 

 is not difficult to visualize that in some bacterial walls (pos- 

 sibly those resistant to lysozyme) peptides may form a cross 

 link between parallel chains of amino sugar oligosaccharides, 

 being linked through muramic acid at each end of the pep- 

 tide. This could be especially the case with those walls 

 containing DAP (or lysine), as there is evidence that both 



