17 



Polypeptides and Related Compounds 



Polypeptides are often intractable, difficultly crystallizable 

 substances. The newer techniques of chromatography, end- 

 group analysis and electrophoresis have facilitated their investi- 

 gation. 



Most of the polypeptides and related compounds listed in this 

 section are antibiotic isolates. Antibiosis may be a primary or 

 only a secondary function of these materials. Polypeptides, of 

 course, have hormonal and other functions in higher animals. 

 Among microorganisms streptomycetes and bacteria have been 

 the richest sources so far, perhaps in part because they have 

 been examined more extensively for antibiotic activity than 

 other microorganisms. 



Special types of polypeptides have been isolated from bac- 

 terial cell walls by fragmentation with lysozyme or bacterio- 

 phage. They also tend to accumulate when bacteria are in- 

 hibited by certain antibiotics. Determination of their structures 

 is beginning to elucidate the nature of the bacterial cell wall as 

 well as the mode of action of the antibiotics involved. 



Some attention has been given to intracellular peptides, prin- 

 cipally in connection with their role in protein synthesis. The 

 fundamental process of polypeptide and protein biosynthesis is 

 just beginning to yield some of its secrets. Before discussing it, 

 some earlier work on simpler polypeptide biosynthesis will be 

 reviewed. 



Glutathione is a widely distributed tripeptide which has a 

 rapid metabolic turnover in yeast and also in mammalian tis- 

 sues. Partly for this reason it has been suggested as an inter- 

 mediate in protein biosynthesis, but because of its reversible 

 oxidation-reduction properties, a respiratory role also has been 

 proposed. In fact, it has not been proved satisfactorily that 

 polypeptides serve as direct precursors for protein synthesis in 



