Enzymatic Interconversion of Isomorphic Fluorescent Nucleosides: Adenosine Deaminase Transforms an Adenosine Analogue into an Inosine Analogue

Adenosine deaminase (ADA), a major enzyme involved in purine metabolism, converts an isomorphic fluorescent analogue of adenosine (thA) into an isomorphic inosine analogue (thI), which possesses distinct spectral features, allowing one to monitor the enzyme-catalyzed reaction and its inhibition in real time. The utility of this sensitive fluorescence-monitored transformation for the high-throughput detection and analysis of ADA inhibitors is demonstrated.