Structure-activity relationship of ligands of human plasma adenosine deaminase₂

Diethylaminoethyl-cellulose chromatography was used to separate the two isoenzymes of adenosine deaminase (EC 3.5.4.4), adenosine deaminase₁ (ADA₁) and adenosine deaminase₂ (ADA₂), in human plasma. One hundred and fifteen purine base, nucleoside, and nucleotide analogs were tested as inhibitors of this partially purified preparation of ADA₂. Coformycin and 2'-deoxycoformycin were by far the most potent inhibitors of this isoenzyme (apparent K_i values 20 and 19 nM, respectively). ADA₂ was also inhibited by nebularine (apparent K_i 1.5 mM) but was resistant to the potent ADA₁ inhibitor (+)-erythro-9(2-S-hydroxy-3-R-nonyl)adenine. α-d-Adenosine also inhibited ADA₂, as did several halogenated purine and adenine base analogs. Structural requirements for the binding of purine analogs to ADA₂ are presented which provide a general basis for the design of specific inhibitors of ADA₂. Such inhibitors may be useful in studies designed to provide an understanding of the physiological role of ADA₂ both in the normal state and in diseases such as human immunodeficiency virus-1 infection where levels in plasma are increased markedly.