UTILIZATION OF AMINO ACIDS AND AMIDES 



261 



Time, minutes 



Figure 7. The oxidation of some amino acids by the D-amino acid oxidase system 

 of Neurospora crassa. Curves 1 to 6 represent, in sequence, the rate of oxidation of 

 methionine, leucine, isoleucine, valine, lysine, and ornithine. The broken horizontal 

 line is drawn at the theoretical value for the complete oxidation of the D-isomer. 

 Redrawn from Horowitz (245), by permission of the Journal of Biological Chemistry. 



corresponding enzyme of sheep kidney reveals that the rates of attack 

 on amino acids and the response to inhibitors of the two systems are 

 somewhat different (47). The enzyme exhibits maximal activity at 

 pH 8.0-8.5 (245). The same or a very similar enzyme is found in 

 mycelial extracts of Aspergillus niger and three Penicillium spp., not in 

 P. sanguineum (143). The different fungal preparations differ some- 

 what in their substrate preferences (47, 143). Penicillium chryso- 

 genum forms much more of the enzyme in a synthetic than in a com- 

 plex medium (143). 



An oxidase system acting on L-amino acids has been shown in 

 Neurospora spp. (47, 87, 536), both in cells and in the medium (48). 

 The enzyme has a somewhat broader substrate specificity than the 

 L-amino acid oxidase of cobra venom (47). Indirect evidence sup- 

 ports the assumption that the prosthetic group is flavin adenine dinu- 

 cleotide (87). Enzyme yield is increased by cultivation with casein 

 hydrolyzate, but this presumed induction occurs only in a low-biotin 

 medium (536). Endogenous amino acids interfere with detection of 

 the enzyme (536). 



The L-amino acid oxidase of Neurospora crassa converts lysine to its 



