ENZYMIC DEGRADATION AND BIOSYNTHESIS 77 



ous nucleotides is not known. At least the probable mecha- 

 nism of the antibiotic action of oxamycin (o-cycloserine) 

 has been amenable to study almost at the level of a single 

 enzyme system. Direct evidence for the inhibition of wall 

 synthesis came from the studies of Shockman '* using Strep- 

 tococcus faecalis and from Strominger, Threnn, and Scott ^^ 

 with Staphylococcus aureus. Both investigations led to the 

 conclusion that oxamycin was acting as a competitive an- 

 tagonist of the incorporation of D-alanine into wall. Strom- 

 inger 3^ has pointed out the close structural relationship of 

 oxamycin to D-alanine as shown below: 



H H H H 



II II 



H— C C— NH2 H— C C— NHo 



II II 



0. .C=0 H .C=0 



Oxamycin D-alanine 



Nucleotides isolated from oxamycin-inhibited cells have 

 given some further evidence of the sequence of the build- 

 ing up of the wall peptide, and Strominger, Threnn, and 

 Scott 63 have shown (Table 24) that the nucleotide accumu- 

 lation induced by oxamycin can be antagonized by D-ala- 

 nine. Strominger ^^ has thus suggested that oxamycin in- 

 hibits the enzymic reaction involved in the addition of 

 D-alanine to the nucleotide UDP-AG-lact-ala-glu-lys. 



It is curious that none of the cell-wall intermediates so 

 far isolated from Staphylococcus aureus contains either gly- 

 cine or N-acetylglucosamine, the other two major cell-wall 

 constituents. It may well be that the peptides attached to 

 the nucleotides isolated up to the present time are far from 

 complete, despite the remarkable similarity in their amino 



