NUCLEIC ACIDS 275 



Table 1. Enzymes Acting on Nucleic Acids, Nucleotides, and Nucleosides* 



Substrate Type of Action Occurrence 



Ribonucleic acid Depolymerization Streptomyces spp. (67, 378), Aspergil- 



lus oryzae (311) 



Deoxyribonucleic acid Depolymerization Neurospora crassa (627), Streptomyces 



sp. (378) 



Nucleotides Deamination Aspergillus spp. (68, 69, 288, 311) 



Nucleosides Deamination Aspergillus oryzae (288, 311, 370), 



Neurospora crassa (350) 



Nucleosides Hydrolysis Aspergillus oryzae (31 1) 



* Dephosphorylation of adenosine phosphates is summarized in Table 1 of 

 Chapter 9. 



This action is often, perhaps usually, carried out by non-specific phos- 

 phatases (316). Hydrolysis of adenosine phosphates, summarized in 

 Chapter 9, and the dephosphorylation of riboflavin monophosphate by 

 extracts of Penicillium chrysogenum (96) are presumably, although not 

 necessarily, effected by such phosphatases. A phosphatase of Strepto- 

 myces sp. acts both on glycerophosphate and on nucleotides (378). 



Diphosphopyridine nucleotide is attacked by a specific enzyme, di- 

 phosphopyridine nucleotidase, which splits off nicotinamide from the 

 dinucleotide, leaving adenosine diphosphate ribose. The enzyme is 

 formed by Neurospora crassa (289); its high concentration in the co- 

 nidia suggests that it is formed only during sporulation (626). The con- 

 centration of enzyme in the mycelium is increased by deficiencies of 

 zinc, nitrogen, or, usually, growth factors (386, 387). The enzyme of 

 N. crassa, unlike the corresponding animal enzyme, is not inhibited by 

 nicotinamide, except at very high concentration, and does not catalyze 

 an exchange reaction between the dinucleotide and free nicotinamide 

 (628). 



Deamination of nucleotides and nucleosides is usually effected by 

 specific enzymes, but an adenyl deaminase of Aspergillus oryzae acts on 

 both types of compound, deaminating adenosine, adenosine-5'-phos- 

 phate, adenosine-3-phosphate, adenosine diphosphate and diphospho- 

 pyridine nucleotide (288). 



These scattered data do not, of course, give a complete or coherent 

 picture of nucleic acid breakdown; they do indicate that catabolism of 

 the purine ribonucleotides in fungi is similar to that in other organ- 

 isms. It seems likely, therefore, that the free purines adenine, hypox- 

 anthine, and guanine are converted to xanthine, which is then oxidized 

 by xanthine oxidase to uric acid (518), the further metabolism of which 

 is described below. 



In Nocardia corallina the pyrimidines thymine and uracil are metab- 

 olized by way of barbituric acid (315); the over-all process, presumably 



