72 MICROBIAL CELL WALLS 



D-glucosamine is a direct precursor of muramic acid and 

 that the latter compound is indeed a D-ghicosamine deriva- 

 tive. 



Incorporation of [^^C] Lysine, [^^C] Diaminopimelic Acid, 

 and [^^C] Glucose info Cell-Wall Lysine and DAP. Meadow 

 and Work ^* investigated the incorporation of radioactive 

 compounds into wall fractions of Escherichia coli mutants 

 requiring either lysine or DAP or both amino acids for 

 growth. All of the mutants tested took up [i^C] lysine, and 

 of the radioactivity incorporated 50 to 60% was accounted 

 for in the cell walls. DAP was not labeled. Ten per cent 

 of the cell-wall lysine of the DAP-requiring mutants was 

 derived from that supplied exogenously; [^^C] diaminopi- 

 melic acid was incorporated into both DAP and lysine of 

 the DAP-requiring mutants and the parent strain. The 

 DAP-dependent, lysine-stimulated mutant 173-25 derived 

 80% of the cell-wall lysine from the exogenous DAP, 

 whereas the corresponding value for the DAP-dependent 

 mutant was 50 to 60%. An alternative route to lysine from 

 glucose was apparent from mutants 173-25 and DAP-de- 

 pendent grown on [^^C] glucose. Labeling of lysine oc- 

 curred, but DAP was unlabeled. Some 10 to 20% of the 

 cell-wall lysine was derived from glucose in these mutants. 



Accumulation and Identification of Cell-Wall Intermedi- 

 ates. The identification of cell-wall intermediates really 

 commenced with the discovery of the accumulation in 

 Staphylococcus aureus of uridine nucleotides in the presence 

 of penicillin. 28. 29 The significance of these nucleotides as 

 possible cell-wall precursors became apparent when the 

 amino sugar was found to be identical to muramic acid 

 and the complete structure for one of the nucleotides 

 was established, as in Fig. 16.^^ This finding was just pre- 

 ceded by Lederberg's ^^' ^^ suggestion that penicillin acted 



