PROTEINS AN D P E P T IDES 25 1 



requirement of Trichophyton rosacea))) is met by carnosine and histi- 

 dylhistidine (136). The widespread occurrence of enzymes hydrolyz- 

 ing peptides to amino acids indicates that in general at least the simple 

 linear peptides will be found to be adequate sources of nitrogen for 

 most fungi. Tricholoma gambosum is unusual in that growth is 

 tripled by glycylglycine, unaffected by glycine (398). 



The requirement of some Myxomycetes for protein has been men- 

 tioned elsewhere (Chapter 10). 



Enzymatic Breakdown of Proteins and Peptides. Following current 

 usage (487) we distinguish two general types of enzyme which attack 

 peptide bonds: 



1. Endopeptidases (proteinases), acting on peptide bonds either in 

 simple peptides or in the interior of a protein chain. 



2. Exopeptidases, acting only on peptide bonds which are adjacent 

 to a free a-amino or a free carboxyl group and therefore restricted 

 generally to hydrolysis of small peptides. 



Both these types are subsumed under the general term protease. 



Surveys of the activity of culture filtrates indicate than an enzyme 

 or enzymes able to hydrolyze gelatin is extremely common among the 

 Fungi Imperfecti (129, 130, 142, 351) and Streptomyces spp. (130, 

 276). Generalization as to other fungi is difficult; gelatin hydrolysis 

 is, however, effected by some ascomycetes (130) and basidiomycetes 

 (53, 629). Among the Mucorales, Rhizopus sp. grows upon and hydro- 

 lyzes several proteins (574), and Mortierella renispora forms active 

 proteases (587, 588). 



However, surveys limited to studies of the culture filtrate cannot 

 be taken as final evidence of lack of a protease. The distribution of 

 proteolytic enzymes between mycelium and culture fluid is conditioned 

 both by age (185) and by the medium (208). This may explain some 

 apparent disagreements (130, 142). 



The most extensive study of the utilization of proteins by fungi and 

 actinomycetes is that of Waksman and Starkey (574). Streptomyces 

 violaceus-ruber and Rhizopus sp. grow upon and decompose casein, 

 zein, gliadin, fibrin, gelatin, and egg albumin; Trichoderma koningi 

 utilizes edestin, zein, gliadin, and casein. In culture, proteins are 

 used more rapidly if there is no other carbon source, but the liberation 

 of ammonia under these conditions is large. 



Other less comprehensive studies show that fungi and actinomycetes 

 generally hydrolyze fibrin (19, 185, 469, 567) and casein (262, 333, 

 485, 489, 524, 567). Keratin-hydrolyzing preparations have been ob- 



