ENZYMES ATTACKING NUCLEIC ACIDS 597 



from aqueous extracts of intestinal mucosa have been described by Brady^^® 

 and by Kalckar.^" 



Specificity. Adenosine deaminase is strictly specific toward adenine ribo- 

 and deoxyribonucleosides/^^ and it is probable that both nucleosides are 

 deaminated by the same enzyme. The amino groups of free adenine and of 

 other purines, pyrimidines, and their derivatives, as well as those of the 

 adenine nucleotides, are resistant to the enzyme. Byrne'^^-' reported, how- 

 ever, that highly purified samples of adenosine deaminase from beef spleen 

 were capable of hydrolysing the amino groups of 2'-aden3dic acid and 2', 

 3',-cyclic adenylic acid as rates corresponding approximately to }^q of the 

 rate of the deamination of adenosine. The pH-optimum for the nucleotides 

 was at pH 5.2, that for the nucleoside between pH 7.5 and 9.3. 3'- and 

 5'-Adenylic acid, DPN, and TPX were not appreciably deaminated. 



pH Optimum. According to Kalckar, the pH optimum of adenosine de- 

 aminase is near the neutral point, but its activity is still considerable at 

 pH 9 and pH 6. 



Stability. Adenosine deaminase of intestinal mucosa is rapidly inactivated 

 by standing at pH 3. On dialysis against water, the activity disappears 

 rapidly and is not restored by combination with the dialysate. 



Inhibitors. According to Brady ,'®^ the activity of intestinal adenosine 

 deaminase is not influenced by low concentrations of fluoride, phosphate, 

 and cyanide ions. 



d. 5'-Adenylic Acid Deaminase 



5'-Adenylic acid deaminase occurs in relatively high concentration in 

 striated muscle^^^ but is practically absent in heart. ^^^'^^ 



5'-Adenylic acid deaminase is a highly specific enzyme which converts 

 5'-riboadenylic acid to inosinic acid. According to Carter,^^^ 5'-deoxyadenylic 

 acid is slowly deaminated by the enzyme. All other amino compounds are 

 resistant, in particular, the o'-adenosine pyrophosphates and 2'- and 3'- 

 adenosine phosphates. Owing to its high specificity, the enzyme is used as a 

 convenient analytical tool for the quantitativ^e determination of 5'-adenylic 

 acid. 



The enzyme can be easily prepared from muscle in enzymically homo- 

 geneous form. Its action can be followed either by ammonia determinations 

 or more conveniently by measuring the changes of the absorption at 265 

 mM caused by the conversion of the adenine to the hypoxanthine group.^"-"" 



'««T. Brady, Biochem. J. 36, 478 (1942). 



'" H. M. Kalckar, /. Biol. Chem. 167, 461 (1947). 



'«^* W. L. Byrne, Abstr. 126th Meeting Am. Chem. Soc, New York p. 73C (1954). 



'88 W. Kutscher and W. Sarreither, Klin. Wcchschr. 26, e05 (1948). 



'«» C. E. Carter, J. Am. Chem. Soc. 73, 1537 (1951). 



"» H. M. Kalckar, J Biol. Chem. 167, 429 (1947). 



