ENZYMES ATTACKING NUCLEIC ACIDS 595 



nucleotides by precipitation of the latter with zinc suKate and barium 

 hydroxide. 



The presence in yeast autolysates and pigeon liver extracts of a phospho- 

 kinase converting the 4-amino-5-imidazolecarboxamide riboside to its ribo- 

 tide was reported by Greenberg.'''^'^ 



V. Enzymes Acting on the Amino Groups of Purine and Pyrimidine 



Compounds 



1, Enzymic Deamination of the Adenine Group 



a. Behavior of Free Adenine 



The tissues of many higher animals do not seem to contain enzymes ca- 

 pable of deaminating free adenine. Some statements to the contrary in the 

 literature are based on indirect evidence such as the decoloration of meth- 

 ylene blue by adenine in the presence of xanthine dehydrogenase. It is now 

 known that the enzymic dehydrogenation of adenine results in the forma- 

 tion of 2 ,8-dihydroxyadenine, and that it is not preceded by its deamination 

 to hypoxanthine.^^"'^^^ The metabolic resistance of the amino group 

 of adenine in rats and dogs is demonstrated by Nicolaier's'^^ observation 

 that ingested adenine is transformed into 2,8-dihydroxyadenine, which 

 forms crystalline deposits in the kidney. The mechanism of this transforma- 

 tion has recently been studied b.y Bendich, Brown, Philips, and Thiersch'^* 

 who found that ingested 2-hydroxyadenine (isoguanine) and 8-hydroxy- 

 adenine can be converted to 2,8-dihydroxyadenine (see also Chapter 25). 

 It should be pointed out, however, that the basis of comparative biochemi- 

 cal studies of this question is not broad enough to permit the conclusion that 

 the resistance of the amino group of free adenine is representative of the 

 behavior of this base in higher animals. 



The desirability of extensive comparatiA-e studies is emphasized by the 

 observations of Duchateau-Bosson and his collaborators, ^"'^^^ who found 

 that extracts of certain lower animals such as anodonta, crustaceans, and 

 insects contain adenine deaminases, but lack enzymes capable of deaminat- 

 ing adenosine or adenylic acid. The authors consider the different distribu- 

 tion of the deaminases of the adenine group in lower and higher animals as 



>"8G. R. Greenberg, Federation Proc. 12, 211 (1953). 



1" A. Nicolaier, Z. klin. Med. 45, 359 (1902). 



i5« A. Bendich, G. B. Brown, F. S. Philips, and J. B. Thiersch, J. Biol. Chew. 183, 



267 (1950). 

 1*' G. Duchateau-Bosson, M. Florkin, and G. Frappez, Compt. rend. soc. biol. 133, 



433 (1940). 

 '" G. Duchateau-Bosson, M. Florkin, and G. Frappez, Compt. rend. soc. biol. 133, 



274 (1940). 

 '6' G. Duchateau-Bosson, M. Florkin, andG. Frappez, Acad. roy. Belg. 27, 169 (1941). 



