345 Polypeptides and Related Compounds 



The spine is composed of alternating muramic acid and N- 

 acetylglucosamine units with branching to adjacent chains from 

 muramic acid, the latter bearing the peptide chain. Penicillin 

 (and perhaps the other antibiotics mentioned) prevents incor- 

 poration of M-P units, and cycloserine prevents incorporation of 

 the terminal two D-alanine units into the side-chain. There is 

 evidence that the dipeptide D-alanyl-D-alanine is preformed be- 

 fore attachment to the peptide chain. 



A review of the chemistry of bacterial cell walls has been 

 published. -^^ 



The newer general theory of polypeptide and protein synthesis 

 can be sketched in only briefly here.^- It is thought that the 

 DNA of the cell nucleus lays out the pattern for replication of 

 the ribosomal RNA, and this pattern is characteristic of each 

 genus, species and type of organism. The ribosomal RNA in 

 turn serves as the template for protein construction. Smaller, 

 more soluble molecules, which seem to be RNA fragments end- 

 ing in the nucleotide adenylic acid, attach themselves at this end 

 to individual amino acids. This attachment requires an enzyme 

 specific for each of the 20 or more amino acids plus ATP. There 

 is also a different transfer RNA molecule for each amino acid. 

 These activated amino acids can be isolated and purified. In 

 this form the amino acid is able to fit into the proper place on 

 the RNA template, probably due to the unique geometry of a 

 short sequence of nucleotides in the chain. Once attached to 

 RNA, condensation of the amino acids to form polypeptides or 

 proteins is facilitated by the favorable arrangement and proxim- 

 ity of the reacting groups. This scheme is believed to be quite 

 general in metabolism. 



A more specific discussion by E. F. Gale of current knowledge 

 about the incorporation of amino acids into bacterial proteins 

 and polypeptides has been published. ^^ It is obvious that con- 

 siderable differences must exist between mechanisms of polypep- 

 tide synthesis in microbial and mammalian metabolism in view 

 of the D-amino acids and other abnormal amino acids which oc- 

 cur in microbial polypeptides. It is apparently these differences 



32 Robert B. Loftfield, Prog. Biophys., Biophys. Chem. No. 8 348 

 (1957); F. H. C. Crick, Symposia of the Society for Exp. Biol. No. 12 

 138 (1958); Mahlon B. Hoagland, Scientific American 201 55 (1959); 

 Alton Meister, Rev. Mod. Phys. 31 210-220 (1959); Leo Szilard, Proc. 

 Nat. Acad. Sci. U. S. 46 277 (1960). 



33 "CIBA Lectures in Microbial Chemistry," E. F. Gale, Synthesis 

 and organization in the bacterial cell, John Wiley and Sons, New 

 York, 1959, 106 pp. 



