In enzymology, a pyrithiamine deaminase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are 1-(4-amino-2-methylpyrimid-5-ylmethyl)-3-(beta-hydroxyethyl)-2-, methylpyridinium bromide, and H<sub>2</sub>O, whereas its 3 products are 1-(4-hydroxy-2-methylpyrimid-5-ylmethyl)-3-(beta-hydroxyethyl)-2-, methylpyridinium bromide, 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 1-(4-amino-2-methylpyrimid-5-ylmethyl)-3-(beta-hydroxyethyl)-2-methylpyridinium-bromide aminohydrolase.