In enzymology, an ATP deaminase (EC 3.5.4.18) is an enzyme that catalyzes the chemical reaction

ATP + H₂O ${\displaystyle \rightleftharpoons }$ ITP + NH₃

Thus, the two substrates of this enzyme are ATP and H₂O, whereas its two products are ITP and NH₃.

This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in cyclic amidines. The systematic name of this enzyme class is ATP aminohydrolase. This enzyme is also called adenosine triphosphate deaminase.

• Chung ST, Aida K (January 1967). "Purification and properties of ATP deaminase from Microsporum audouini". J. Biochem. 61 (1). Tokyo: 1–9. PMID 6048966.