78 THE PLANT CELL WALL 



Amino acids 



alanine aspartic acid 



glutamic acid glycine 



diamino pimelic acid serine 



lysine 

 Hexoses and amino sugars 



glucose N-acetyl glucosamine 



glucosamine muramic acid (3-O-D-carboxyethyl 



hexoseamine) 



galactose chondrosamine 



rhammose 



mannose 



arabinose 



galactosamine 



Interestingly, some bacterial walls are relatively rich in the D-iso- 

 mers, of alanine and glutamic acid. In Streptococcus faecalis for exa- 

 mple 25 per cent of the alanine and 85 per cent of the glutamic 

 acid exist in the D-form. In Lactobacillus, over half of the alanine 

 and two-thirds of the glutamic acid are D-isomers. Although half 

 of the alanine from the wall of Staphylococcus aureus occurs in 

 the D-form, the glutamic acid is almost entirely of the D-form. 

 In general, D-alanine is most widespread among various bacterial 

 walls, D-lysine is also known to occur, but diaminopimelic acid 

 occurs most frequently as the meso-form. 



These and other constituents are in turn organized into poly- 

 saccharides, polymeric hexosamines, peptides, peptide-polysac- 

 charide complexes, proteins (including wall antigens), lipoproteins, 

 and glycoproteins. 



Among the peptides found in various bacteria, the combinations 

 alanine— glutamicacid-diaminopimelic acid or alanine-glutamic 

 acid-lysine recur, sometimes with aspartic acid, glycine or serine 

 in addition. Cyclic peptides containing only lysine and aspartic 

 acid have also been demonstrated, but may be artifacts of acid 

 hydrolysis. Thus far, the presence of either of diaminopimelic 

 acid or lysine in a particular instance precludes the presence of 

 the other. 



