66 MICROBIAL CELL WALLS 



Chitin in an insoluble form was thus synthesized from UDP- 

 acetylglucosamine, soluble chitodextrin, and an activator.^s 

 Higher molecular weight chitodextrin was the most effec- 

 tive primer. The enzyme system was in a particulate form. 



Bacterial Cell Walls. Three main lines of investigation 

 have been pursued in studies of the biosynthesis of bacte- 

 rial walls. They include (1) biosynthesis of individual wall 

 compounds, (2) synthesis of mucopeptide and incorporation 

 of radioactive compounds into walls, and (3) isolation and 

 characterization of possible intermediates accumulating dur- 

 ing inhibition of wall synthesis. 



Biosynthesis of Muramic Acid. Attempts to elucidate 

 the origin of the O-lactyl side chain of muramic acid were 

 made by Strominger.^* He discovered that Staphylococcus 

 aureus contained an enzyme catalyzing the transfer of pyru- 

 vate from 2-phosphoenolpyruvate (PEP) to UDP-acetylglu- 

 cosamine by the following reaction: 



UDP-AG -f PEP -^ UDP-AG-pyruvate + Pi 



Although the rate of the reaction in this enzyme system 

 was about one fifth of the rate of UDP-acetylglucosamine 

 formation, Strominger ^s has suggested that in 10 minutes 

 at 37° the enzyme could synthesize sufficient substituted 

 N-acetylglucosamine required for the wall of Staphylococ- 

 cus aureus, thus achieving this feat well within the mean 

 generation time of the organism. 



Strominger and Scott ^^ have also detected a small en- 

 zymic conversion of UDP-acetylglucosamine-[i-^C]-pyruvate 

 to UDP-acetylglucosamine-[i^C]-lactic acid by extracts of 

 Staphylococcus aureus. The net reaction, however, was 

 small, and the mechanism of synthesis of muramic acid and 

 its uridine nucleotides still remains to be established. 



