ENZYMIC DEGRADATION AND BIOSYNTHESIS 67 



That the 3-O-carboxyethyl residue of muramic acid is 

 derived from pyruvate was further substantiated in recent 

 experiments performed by Richmond and Perkins ^^ with 

 intact cells of Staphylococcus aureus, incubated under con- 

 ditions favoring only cell-wall synthesis.*^ A cell wall syn- 

 thesized with [^^C] glucose in the absence of alanine showed 

 similar specific activities per microgram of carbon for both 

 glucosamine and muramic acid. However, when the wall 

 was synthesized in the presence of alanine, the muramic 

 acid formed had the specific activity of the side chain re- 

 duced by 75%. Generally labeled [i^C] alanine and [i^C] 

 aspartic acid could act as precursors of the muramic acid 

 side chain. The two noncarboxyl atoms of the side chain 

 of muramic acid yield acetaldehyde when heated at 100° 

 with 86% sulfuric acid for 17 minutes (Strange and Kent ^~), 

 whereas the carboxyl group yields carbon monoxide. These 

 facts enabled Richmond and Perkins ^^ to conclude from 

 experiments with [^^C] alanine that all three carbon atoms 

 of the alanine can act as precursors of the muramic acid 

 side chain without inversion and that these results are con- 

 sistent with the idea that phosphoenolpyruvate is the im- 

 mediate precursor. 



Synthesis of Wall Mucopeptides and Incorporation of 

 Radioactive Compounds into Walls. The synthesis of cell- 

 wall mucopeptides by washed suspensions of two different 

 strains of Staphylococcus aureus in defined incubation mix- 

 tures was independently reported by Mandelstam and Rog- 

 ej-s4i,43 and by Hancock and Park.*^ The increase in wall 

 mucopeptide content of Staphylococcus aureus incubated 

 in buffers containing glucose and various combinations of 

 the amino acids known to occur in the wall varied from 

 20 to 150% in one hour at 37°. The results of the experi- 

 ments performed by Mandelstam and Rogers ^^ are pre- 



