2(34 NITROGEN NUTRITION AND METABOLISM 



has been suggested that oxidative deamination, decarboxylation, and 

 oxidation reactions occur as follows (353, 584): 



Tryptophan -+ indolepyruvic acid -> 

 indoleacetaldehyde — > indoleacetic acid (7) 



Although from time to time it is reported that indoleacetic acid in- 

 creases the growth of fungi, most studies have not shown this (367, 

 438, 584) or show it only under special circumstances (235). However, 

 acceleration of the maturation of the meiosporangium of Allomyces 

 arbuscula on agar media, perhaps by an effect on the sporangium wall, 

 indubitably occurs (341). Growth inhibition by indoleacetate is com- 

 mon (71, 235, 438, 449); in Nectria galligena inhibition is reduced by 

 biotin (400, 401). It has been argued, on the basis of inhibition studies 

 alone, that indoleacetate is an essential metabolite of Diplodia natalen- 

 sis (195); the evidence, however, is subject to other interpretations. 

 Destruction of indoleacetic acid occurs in the cultures in which it is 

 produced (584), and cell-free enzyme systems of several basidiomycetes 

 inactivate the auxin (77, 148, 479, 545). The enzyme of Omphalia 

 flavida is highly specific, oxidizing indoleacetate with equimolar 

 amounts of oxygen at pH 3.5; the first product of the reaction is not 

 known (430, 431). 



Threonine is cleaved by Neurospora crassa to glycine and acetalde- 

 hyde (565); this non-oxidative reaction occurs also in animal systems 

 (214). 



The breakdown of histidine in bacterial and animal preparations 

 proceeds via urocanic and glutamic acids (339, 516); this system has 

 not been studied in fungi, although glutamate does accumulate during 

 histidine breakdown by Streptomyces venezuelae (212). Histidine de- 

 carboxylase could not be detected in Claviceps purpurea or Aspergillus 

 spp. (585). 



The oxidation of cysteine sulfur is mentioned in Chapter 9, and the 

 role of methionine as a methyl donor in Chapter 6. No other signifi- 

 cant information on the breakdown of the carbon chains of these 

 compounds by fungi is available. Cysteine desulfhydrase is not de- 

 tectable in Penicillium chrysogenum; its occurrence in bacteria is re- 

 viewed by Fromageot (180). 



Arginine is broken down in the urea cycle, discussed later. Strep- 

 tomyces griseus extracts contain an inducible enzyme which converts 

 arginine to guanidinobutyramide (539, 540). 



Glutamic acid is probably the principal donor of amino groups in 

 transaminations (p. 267); in the process it is converted to a-ketoglu- 

 taric acid. Hence its carbon chain may be assumed to be oxidized by 



