36 MICROBIAL CELL WALLS 



TABLE 14 



Percentage of Glutamic Acid, Aspartic Acid, and Alanine in the 

 D-configuration in Cell Walls 



(% of total in D-form) 



Glutamic Aspartic 



Acid Acid Alanine 



* Data from Ikawa and Snell.^i 



Identification of N-Terminal and C-Terminal Amino 

 Acids. Attempts to apply some of the classical techniques 

 for determining the chemical structure of proteins to bac- 

 terial cell walls have been complicated by some of the un- 

 usual features of cell-wall composition [see foregoing 

 (rt)-(g)]. The cell-wall constituents possessing free amino 

 groups can be readily identified by reacting the walls with 

 l-fluoro-2,4-dinitrobenzene (FDNB)/^ the method intro- 

 duced by Sanger ^" for the determination of the N-terminal 

 residues in proteins. However, the interpretation of results 

 with bacterial walls is complicated by the presence of ester- 

 linked alanine in the teichoic acids. -^ O-alanyl residues 

 would thus behave as N-terminal amino acids. With walls 

 from Micrococcus lysodeikticus and Sarcina lutea that are 



