64 



MICROBIAL CELL WALLS 



HO 



CIIoOH 



CH. 



H NHCOCH. 



O H NHCOCH3 



/ 



CH3CHCONH (ala — glu — lys — gly) 



V 2 111 



Streptomyces amidase 



Fig. 15. Structure of mucopeptide in lysozyme digest and bond sensi- 

 tive to streptomyces amidase. is 



Micrococcus lysodeikticiis/- but in other walls O-esters can- 

 not account for the greater resistance of the walls to diges- 

 tion with lysozyme. The possibility of different linkages 

 between amino sugars of the backbone has been suggested. ^^ 

 Resistance to lysozyme could also be explained by differences 

 in the ratios of amino sugars, relatively few disaccharide 

 units, branching points, single amino acid substituents at- 

 tached to muramic acid, and a high frequency of cross- 

 linked peptides between muramic acid residues (two types 

 of structures discussed in Chapter 2). There are many in- 

 triguing possibilities, and it will be of great interest to find 

 out the factors responsible for the resistance of the walls of 

 an organism such as Bacillus cereus, which contains such a 

 large amount of amino sugar in the wall (30%). ^^ 



Biosynthesis of Microbial Walls 



The biosynthesis of microbial walls is now beginning to 

 attract much attention, and within the brief space of the 

 last couple of years a great deal has been learned. The 

 discovery of the accumulation of uridine nucleotides in 



