In enzymology, a sepiapterin deaminase () is an enzyme that catalyzes the chemical reaction sepiapterin + H2O xanthopterin-B2 + NH3 Thus, the two substrates of this enzyme are sepiapterin and H2O, whereas its two products are xanthopterin-B2 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 sepiapterin aminohydrolase. References EC 3.5.4 Enzymes of unknown structure