In enzymology, a pterin deaminase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are 2-amino-4-hydroxypteridine and H<sub>2</sub>O, whereas its two products are 2,4-dihydroxypteridine and NH<sub>3</sub>.
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 2-amino-4-hydroxypteridine aminohydrolase. This enzyme is also called acrasinase.