PROTEINS AND PEPTIDES 253 



endopeptidase formation by Aspergillus oryzae shows, as expected, 

 optima for carbon source, salts, iron, and temperature (352). 



Culture nitrates or mycelial extracts of fungi commonly, perhaps uni- 

 versally, hydrolyze peptides. However, it is hazardous at present to 

 identify this activity with particular exopeptidases known from other 

 sources or even to state categorically that endopeptidase activity has 

 been excluded in many of the reports. Aspergillus parasiticus forms 

 four exopeptidases, including an aminopeptidase which is activated 

 by zinc and by reducing agents (284); these same activators affect the 

 aminopeptidase of Penicillium spp. (52). A number of fungi — Asper- 

 gillus spp., Penicillium spp., Cunninghamella sp., Coprinus radians, 

 and Agaricus campestris — form a dipeptidase, an aminopeptidase, and 

 a carboxypeptidase; many of these fungi also elaborate an aminotri- 

 peptidase assayed with triglycine, and a glycylglycine dipeptidase (53). 

 A similar range of activities is reported for Mortierella renispora, 

 Chaetomium sp., and other fungi (336). 



Glycylglycine dipeptidase of Aspergillus oryzae is activated by co- 

 balt (115), as is the same enzyme from other sources (487). Dipepti- 

 dases also are produced by Physarum polycephalum (244), Piricularia 

 oryzae (259), Penicillium notatum (263) and other fungi (336, 403). 



Hydrolysis of some amides may be effected by enzymes which also act 

 on peptides or proteins; "hippuricase," for example, may be identical 

 with a carboxypeptidase (182). 



It appears, in summary, that fungi produce a battery of enzymes 

 attacking peptides of low molecular weight. Information is at present 

 too fragmentary for a detailed classification of the fungal exopepti- 

 dases; the availability of synthetic test substrates (487) makes the de- 

 velopment of such a classification a possible enterprise. 



Peptides of Fungi and Actinomycetes. Following Bricas and Froma- 

 geot (76), we may define peptides as compounds of low molecular 

 weight which contain two or more amino acids and peptide or pepti- 

 doid bonds. This excludes certain compounds such as pantothenic 

 acid and biocytin (Chapter 10), in which one amino acid and a non- 

 amino acid moiety are joined by a peptide linkage. The naturally- 

 occurring peptides may be classified as homeomeric — consisting only of 

 amino acids — and heteromeric — consisting of amino acids and a non- 

 amino acid moiety. 



Glutathione perhaps deserves first place in this discussion because 

 of its probable ubiquity in living cells, its vital role in triose phosphate 

 dehydrogenase, and its probable role in peptide synthesis (76). Using 



