Adenosine deaminase (ADA) and adenylic acid deaminase (AMPDA) are enzymes that catalyze the hydrolytic deamination of various purine nucleosides. In light of recent reports, ADA and AMPDA may be considered as valuable biocatalysts in nucleoside chemistry. Here, they can find many synthetic applications in the transformation of purine nucleosides that are modified in the base or the ribose moiety. Their use can be extended to carbocyclonucleosides or acyclonucleosides as well.