CHEMISTRY OF CELL WALLS 37 



devoid of the teichoic acids, the DNP-alanine detectable on 

 reaction with FDNB probably represents the N-terminal 

 residue of the wall peptides, and from this data a subunit 

 size can be tentatively suggested.**' The contribution of 

 the teichoic acids to the N-terminal alanine residues can 

 be surmised from a comparison of the amounts of DNP- 

 alanine obtained from the walls of Micrococcus lysodeikti- 

 ciis (23 /xM/g) with those of Staphylococcus aureus (170 

 fxM/g) and Lactobacillus arahinosus (120 ^M/g), both rich 

 in teichoic acids.*^ The relatively small number of N-termi- 

 nal gi'oups in walls other than those containing large 

 amounts of teichoic acids is perhaps not surprising, as the 

 "free" amino groups of peptides would be required for 

 amide bonding to muramic acid. The comparatively low 

 yields of N-terminal residues could, of course, be equally 

 well explained by cyclic peptide structures or N-acetyla- 

 tion of amino acid residues. 



The application of carboxypeptidase for the identification 

 of C-terminal residues of walls of Gram-positive bacteria 

 has not been successful (Perkins and Rogers,^^ Salton ^^). 

 This is not at all surprising, since the cell-wall peptides 

 contain D-isomers of several amino acids. Hydrazinolysis,^*^ 

 on the other hand, has been much more successful, and with 

 some walls this method has given very clean results, al- 

 though their interpretation poses several interesting prob- 

 lems of the molecular structure of walls. The yields of 

 C-terminal amino acids (uncorrected for any losses during 

 hydrazinolysis) from several cell walls and lysozyme-digest 

 products are given in Table 15. 



Whether we are really dealing with C-terminal residues 

 in the protein sense (i.e., at the end of a peptide chain) is 

 not known. It is conceivable that special types of linkages 

 of amino acids in the wall peptides could give false "C-termi- 

 nal" values in just the same way as O-alanyl groups behave 



