258 NITROGEN NUTRITION AND METABOLISM 



or artificial mixture of different amino acids than with any single 

 amino acid (442). 



Asparagine deserves special attention, since it is so often one of the 

 best sources of nitrogen for fungi and actinomycetes. The question is: 

 does the amide have some particular value, or is asparagine merely a 

 source of aspartic acid and extra nitrogen? Asparagine and aspartate 

 are about equivalent for many fungi (25, 46, 275, 604), but the amide 

 is superior to the acid for Tricholoma imbricatum (398), Piricularia 

 oryzae (406), and Leptographium sp. (317), and, at least as sole nitro- 

 gen source, for Phycomyces blakesleeanus (323). No decision can be 

 reached at this time, nor can it be until possible pH effects of utiliza- 

 tion of the two compounds are excluded; the role of pH is emphasized 

 by the response of Coprinus hiascens to asparagine and aspartate (165). 

 It is significant in this connection that aspartic acid does not replace 

 the asparagine requirement of a mutant of Neurospora crassa (523). 

 It is also known that asparagine is in some systems more active as an 

 amino group donor to transamination reactions than is aspartate (354, 

 355). Piricularia oryzae utilizes the amide nitrogen of asparagine 

 more rapidly than the amino nitrogen (260). 



Glutamine has been little studied in fungi; it is superior to glutamic 

 acid as a nitrogen source for Tricholoma gambosum (398) and is gen- 

 erally utilized by other basidiomycetes (275). Like asparagine, it is 

 active in transamination (354, 355), and it may also have a role in 

 transpeptidation. One specific and important function of glutamine 

 has been pointed out (Chapter 5), the provision, by transamidation, 

 of the amino group of glucosamine. 



As mentioned later (Chapter 12) spore germination of Neurospora 

 crassa is inhibited by amino acids, e.g., glycine at 50 pg per milliliter 

 (453). Hydroxyproline at about this level is markedly inhibitory to 

 Trichophyton spp. and other dermatophyte fungi (443, 471). Hy- 

 droxyproline is not toxic to other fungi; its action on Trichophyton 

 mentagrophytes is partially reversed by L-proline (443). Methionine 

 and phenylalanine are also inhibitory to Trichophyton spp. (506), 

 methionine to other fungi (169). The possibility that toxicity is ex- 

 erted at the cell surface deserves exploration, in view of studies on 

 histidine mentioned below. 



The aliphatic amides, although possibly acted upon by fungal en- 

 zymes (p. 265), are not generally utilizable; acetamide may be an excep- 

 tion (39, 63, 120). 



Utilization of the D-isomers of the amino acids is specific; thus, 

 Apodachlya brachynema utilizes D-leucine, but Leptomitus lacteus does 

 not (463), and Ustilago scabiosae can grow with D-valine, D-isoleucine, 



