The effects of allopurinol, acyclovir and theophylline on the activity of adenosine deaminase (ADA) were studied in 50 mM sodium phosphate buffer pH 7.5 at 27°C, using a UV– Vis spectrophotometer. Adenosine deaminase is inhibited by these ligands, via different types of inhibition. Allopurinol, as a transition state analog of xanthine oxidase, and acyclovir competitively inhibit the catalytic a...