254 NITROGEN NUTRITION AND METABOLISM 



an iodometric method of possibly doubtful specificity, Miller and 

 Stone (366) report the presence of glutathione in mycelium of Neuru- 

 spora sitophila and other fungi. The common occurrence in fungi of 

 triose phosphate dehydrogenase (Chapter 7), of which glutathione is 

 the prosthetic group (308), indicates that the peptide is at least wide- 

 spread among fungi and actinomycetes. A mutant of Glomerclla sp. 

 requires glutathione, and nutritional evidence suggests that it is defi- 

 cient in the ability to form the component dipcptide y-glutamylcys- 

 teine (348). 



The actinomycins form a group of related antibiotics first discovered 

 by Waksman and Woodruff (575) and produced by Streptomycrs spp. 

 (79) and by Micromonospora sp. (157). Chemically they are hetero- 

 meric peptides; all contain the same chromophore, or despeptido-acti- 

 nomycin, of the structure (81): 



HO 



H 3 C I CH 



The peptide chain distinguishes the various actinomycins, very many 

 of which have been described (78, 79); the identity of the individual 

 actinomycins is much in doubt, since it appears that many of the iso- 

 lated fractions are in fact different mixtures of the same components 

 (452). A given strain may produce one type or mixture early, an- 

 other later, in the culture cycle (210). 



Several other antibiotics of Streptomyces spp. are or contain peptide 

 chains; examples include viomycin, streptothricin and streptolin (76), 

 and the less completely characterized amphomycin (230) and levomycin 

 (95). Polypeptide antibiotics are very common also among the true 

 bacteria. Such compounds are not usual among the filamentous fungi, 

 although penicillin (Chapter 6) may be considered as a heteromeric 

 cyclic peptide, and the toxin of Helminthosporium victoriae is prob- 

 ably a polypeptide (421a). 



Lycomarasmin, reviewed by Gaumann (190), is a peptide produced 

 by Fusarium oxysporum f. lycopersici; although it is able to cause 

 wilting of plants, its role in natural pathogenesis in the wilt diseases is 

 in dispute. It appears in quantity in the medium fairly late in the 

 culture cycle, after autolysis has begun (Figure 5). A heteromeric 

 peptide, its structure has been determined (609) to be N-(a-[«-hydroxy- 

 propionic acid])-glycyl-asparagine. 



