Involved in thiamine salvage by hydrolyzing the thiamine breakdown product 4-amino-5-aminomethyl-2-methylpyrimidine (amino-HMP) to 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) (PubMed:25014715). Has a high formylamino-HMP amidohydrolase activity (PubMed:25014715). No activity with other thiamine degradation products such as thiamine mono- or diphosphate, oxothiamine, oxythiamine, thiamine disulfide, desthiothiamine or thiochrome as substrates (PubMed:25014715). Does not display thiaminase II activity, as it is unable to hydrolyze thiamine (PubMed:25014715). Is able to carry out two successive steps in the salvage of thiamine breakdown product, whereas two separate enzymes are required in Bacillus species (Probable). May also serve a damage pre-emption function by hydrolyzing products that would otherwise do harm (Probable). 4-amino-5-aminomethyl-2-methylpyrimidine + H2O = 4-amino-5-hydroxymethyl-2-methylpyrimidine + NH4(+) H2O + N-formyl-4-amino-5-aminomethyl-2-methylpyrimidine = 4-amino-5-aminomethyl-2-methylpyrimidine + formate kcat is 0.00281 sec(-1) for formylamino-HMP. kcat is 0.00015 sec(-1) for amino-HMP. Cofactor biosynthesis; thiamine diphosphate biosynthesis. Expressed in roots and shoots. Expression increases during seed development. No visible phenotype. Used for 3D-structure determination. Belongs to the thiaminase-2 family.