PROTEINS AND P F. P T I I) E S 



255 



Figure 5. Growth and lycomaras- 

 min formation (in the culture 

 medium) in Fusarium oxysporum I. 

 lycopersici. Redrawn from Dimond 

 and Waggoner (127), bv permission 

 of Pliytopathology. 



Dry weight 



60 

 Time, days 



100 



Lycomarasmin forms a complex with iron, and it is the complex 

 which is responsible for all or most of its toxicity to higher plants 

 (190, 564). Both free lycomarasmin and the iron complex are rela- 

 tively unstable in solution (128). 



Two heteromeric peptides, enniatin A and enniatin B, are also pro- 

 duced by Fusarium spp. (190, 417, 418) and, like lycomarasmin, cause 

 wilting of plants (193). 



Aspergillus fumigatus and Streptomyces spp. release into the culture 

 medium a diketopiperazine, the anhydride of L-leucyl-L-proline, pre- 

 viously known only from animal sources (280). 



Lastly, the toxins of Amanita spp. may be mentioned; they have been 

 reviewed most recently by Block, Stephens, and Murrill (61). Origi- 

 nally, the hemolytic nitrogenous glucoside phallin was separated from 

 "amanitin" (8, 466); later, it was discovered that the second material 

 is in fact three closely related peptides, now known as a-amanitine, 

 /?-amanitine, and phalloidine. The European form of Amanita phal- 

 loides contains all three of these compounds, amounting in total to 

 about 0.005 per cent of its fresh weight (596). Other species of 

 Amanita have only one or two of the peptides, and most species have 

 none (61). A complete structure has been proposed only for phal- 

 loidine (597), although the three toxins have been separated and 

 purified (60, 594, 596). The suggested structure, that of a bicyclic 

 hexapeptide, is unusual in that two amino acids arc joined by a sulfur 

 bridge. 



The excretion of unidentified nitrogenous compounds, primarily 

 peptides, into the medium during growth has been studied by Morton 

 and Broadbent (374). This excretion occurs in Scopulariopsis brevi- 

 caulis during the period of rapid growth, i.e., it is not an autolytic phe- 



