Adenosine deaminase substrate specificity

Adenosine aminohydrolase (adenosine deaminase) is found in all types of cells and is apparently an important catabolic enzyme for the regulation of cellular metabolism. It has been isolated from a number of sources and the substrate specificities of the various enzymes are similar, since a low degree of specificity R... 

In rat heart the control rate of adenylate deaminase activity was lower, and that of adenylate dephosphorylation higher than in lung. Most of the ammonia formed from adenylate was therefore due to adenosine deaminase activity. ATP stimulated adenylate deaminase to almost the same relative degree in heart as in lung, but due to a marked inhibition of dephosphorylation the total amoimt of ammonia formed was less in heart. These data also raise questions concerning the identity and substrate specificities of the enzyme(s) that dephosphorylate adenylate and inosinate. 

In different tissues, for reasons that we do not understand, administration of 3-DZA can produce either the inhibition of the hydrolase, with the resulting increase in the intracellular concentration of AdoHcy, or its utilization as a substrate with the formation of 3-DZA-Hcy. In most tissues both effects can be observed. 3-DZA, like adenosine, is readily taken up by the cell through facilitated diffusion, and is extremely specific in its mode of action. As mentioned above, 3-DZA is neither a substrate nor an inhibitor for adenosine deaminase and adenosine kinase. It is, therefore, not incorporated in the acid soluble nucleotide pool and hence is not... 

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