In enzymology, a diaminohydroxyphosphoribosylaminopyrimidine deaminase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine and H<sub>2</sub>O, whereas its two products are 5-amino-6-(5-phosphoribosylamino)uracil 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 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine 2-aminohydrolase. This enzyme participates in riboflavin metabolism.
As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes , , , , , and .