ENZYMIC DEGRADATION AND BIOSYNTHESIS 71 



minutes of exposure to penicillin. To what extent this lack 

 of agreement is a reflection of strain differences has not 

 been determined. 



It is of interest to note that the partially disrupted cells 

 of Staphylococcus aureus investigated by Gale and Folkes *^ 

 will incorporate a high proportion of the total [^^C] amino 

 acid uptake of an amino acid such as glycine into the tri- 

 chloroacetic acid insoluble, cell-wall fraction (Gale, Shep- 

 herd, and Folkes *^). Whether the mucopeptide was in the 

 form of finished wall or simply TCA-precipitable material 

 was not established. It would be of interest to know 

 whether the disrupted cells retain an intimate contact be- 

 tween the acceptor cell wall and the sites of new mucopep- 

 tide synthesis. In attempting to localize the sites of syn- 

 thesis of mucopeptides, Brookes, Crathorn, and Hunter ^° 

 have investigated the time course of the uptake of [^^C] 

 amino acids (L-alanine, diaminopimelic acid, and L-aspartic 

 acid) into the wall, membrane, and protoplasmic fractions 

 of Bacillus megaterium. They concluded from their results 

 that the mucopeptide components are synthesized at sites 

 on or closely associated with the cytoplasmic membrane. 



Incorporation of [1-^*C] a, ^-methyl-N-acetyl-D-glucos- 

 aminide into Cell Walls. The organism Lactobacillus bi- 

 fidus var. pennsylvanicus has a specific growth requirement 

 for N-acetyl-D-glucosamine, preferably in the form of ^-gly- 

 cosides. ^^ That this requirement was associated with wall- 

 synthesizing systems has been shown by Zilliken's experi- 

 ments ^--^^ in which the proportion of morphologically bi- 

 zarre and bifid forms decreases with increasing amounts of 

 the glucosaminide growth factors; [l-^^C] /3-methyl-N-acetyl- 

 D-glucosaminide is incorporated into the cell walls of Lacto- 

 bacillus bifidus, the specific activity in the muramic acid 

 being 19,000 cpm/mole compared to 21,000 cpm /mole for 

 the starting material. Zilliken ^2, 53 concluded that N-acetyl- 



