Catalyzes the hydrolytic deamination of adenine to hypoxanthine. Plays an important role in the purine salvage pathway and in nitrogen catabolism. Also exhibits a low activity towards N(6)-substituted adenines that are commonly known as the plant hormones cytokinins. adenine + H(+) + H2O = hypoxanthine + NH4(+) Binds 1 zinc ion per subunit. Optimum pH is 7.0. Optimum temperature is 30-37 degrees Celsius. Reduced when grown in a poor nitrogen source medium and strongly down-regulated when cells enter quiescence under nutrient-limiting conditions. Probably ubiquitinated when cells enter quiescence in response to nutrient limitation, since it is specifically degraded via a process requiring the F-box protein SAF1 and components of the SKP1-Cullin-F-box complex. Present with 20700 molecules/cell in log phase SD medium. Belongs to the metallo-dependent hydrolases superfamily. Adenosine and AMP deaminases family. Adenine deaminase type 2 subfamily.