322 F. SCHLENK 



the mechanisms (14) to (18) have been studied in detail. In some instances 

 the reversibihty has not yet been demonstrated. 



a. Inosine^ Adenosine 



Adenosine deaminase is the best studied of these enzymes.' •^^"'*'' The 

 specificity is usually high in the tissue enzyme which attacks only adenosine 

 and deoxyadenosine ;^^ '^^ no other related nucleosides with substituents in 

 the purine or carbohydrate are attacked/^ nor is free adenine deaminated. 

 In L. helveticus a deaminase is found which catalyzes the deamination of 

 adenine riboside but not of adenine deoxyriboside. This is in contrast to a 

 number of other bacteria, such as E. coli and L. casei, which have a deami- 

 nase resembling that from tissues.^' Relatively low specificity is shown by 

 the adenosine deaminase from Aspergillus oryzae}^ Kaplan et al}^ found 

 that the purified enzyme deaminates adenosine, 5-adenylic acid, 3-adenylic 

 acid, diphosphopyridine nucleotide, adenosine diphosphate, adenosine tri- 

 phosphate, and the fragment of DPN consisting of adenosine diphosphate 

 and ribose (DPN minus nicotinamide). Deoxyadenosine was not tested, 

 and adenine, triphosphopyridine nucleotide, and 2-adenylic acid were not 

 deaminated. 



6. 5- Adenylic Acid Deaminase 



Another deaminase, which is specific for 5-adenylic acid, was discovered 

 by Schmidt" in muscle tissue. It attacks 5-deoxyadenylic acid but not 

 3-adenylic acid.*^^ More recent investigations of this enzyme have resulted 

 in confirmation and extension of Schmidt's data.^-^' This deaminase occurs 

 in voluntary muscle, nerve tissue, auricular muscle of the heart, and in 

 erythrocytes; it is lacking in kidney, liver, intestine, and smooth muscle.^'* 



c. Amination of Inosine and hiosinic Acid 



The deaminations caused by adenosine deaminase and by 5-adenylic acid 

 deaminase go to completion, and no reversal with an excess of ammonia has 

 been observed. Glutamine has been assumed by many authors to be the 

 donor of the amino group. Suggestive evidence for this hypothesis has been 



«P. Gyorgy and H. Rothler, Biochem. Z. 187, 194 (1927). 



^«G. Schmidt, Z. physiol. Chem. 179, 243 (1928). 



" T. Brady, Biochem. J. 36, 478 (1942). 



« H. M. Kalckar, J. Biol. Chem. 167, 445 (1947). 



*^ H. K. Mitchell and W. D. McElroy, Arch. Biochem. 10, 351 (1946). 



*» N. O. Kaplan, S. P. Colowick, and M. M. Ciotti, J. Biol. Chem. 194, 579 (1952). 



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



" G. D. Lu and D. M. Needham, Biochem. J. 35, .392 (1941). 



" H. B. Stoner and H. N. Green, Biochem. J. 39, 474 (1945). 



" E. J. Conway and R. Cooke, Biochem. J. 33, 479 (1939). 



