ENZYMIC DEGRADATION AND BIOSYNTHESIS 81 



mechanism of transglycosylation, commonly encountered in 

 the biosynthesis of many compounds, including the struc- 

 tural polymer chitin. Thus the basis of these reactions in- 

 volving uridine and cytidine nucleotides (the only two 

 classes so far implicated in bacterial wall synthesis) would 

 be analogous to that found for chitin synthesis by Glaser 

 and Brown.^^ 



Nucleotide — wall component -|- acceptor (wall) 



-» acceptor — wall component -|- nucleotide diphosphate 



Two major pathways for biosynthesis of part of the bac- 

 terial wall have been suggested by Strominger ^s- 65 and are 

 presented in Figs. 18 and 19. For those organisms possess- 

 ing an amino sugar backbone, a further part of the biosyn- 

 thetic scheme can be suggested, since some of the possible 

 intermediates are already known (UDP-AG-lact, UDP-AG, 

 muramic acid-6 phosphate ^^). This hypothetical pathway 

 illustrated in Fig. 20 could be envisaged as being integrated 

 with the other pathways (Figs. 18, 19), thereby adding the 

 muramic acid-peptide residue to an amino sugar backbone 

 already built on to the cell-wall acceptor. 



Epideictic 



In the period of the last ten years a new class of structural 

 heteropolymers has been discovered in bacterial cell walls 

 and in at least some of the related blue-green algae. We 

 are just beginning to understand some of the properties and 

 structures of these mucopeptide and mucopolysaccharide 

 substances, and some exciting details of the biosynthesis of 

 the major structural component of microbial cells are be- 

 ginning to emerge. It is perhaps fortunate for mankind 

 that nature saw fit to encase bacteria in a wall containing 

 amino sugar and amino acid structures not normally en- 



