Catalyzes an amino-pyrimidine hydrolysis reaction at the C5' of the pyrimidine moiety of thiamine compounds, a reaction that is part of a thiamine salvage pathway. Thus, catalyzes the conversion of 4-amino-5-aminomethyl-2-methylpyrimidine to 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP). To a lesser extent, is also able to catalyze the hydrolytic cleavage of thiamine; however, this thiaminase activity is unlikely to be physiologically relevant. Therefore, is involved in the regeneration of the thiamine pyrimidine from thiamine degraded products present in the environment, rather than in thiamine degradation. 4-amino-5-aminomethyl-2-methylpyrimidine + H2O = 4-amino-5-hydroxymethyl-2-methylpyrimidine + NH4(+) H2O + thiamine = 4-amino-5-hydroxymethyl-2-methylpyrimidine + 5-(2-hydroxyethyl)-4-methylthiazole + H(+) kcat is 22.0 min(-1) for the hydrolysis of 4-amino-5-aminomethyl-2-methylpyrimidine. Catalyzes the hydrolysis of aminopyrimidine 100 times faster than the hydrolysis of thiamine. Cofactor biosynthesis; thiamine diphosphate biosynthesis. Homotetramer. Strongly repressed by thiamine. Inactivation of this gene causes a delay in sporulation, but does not affect cell growth and the production of extracellular enzymes (PubMed:1898926). The deletion mutant does not require a hydroxypyrimidine source as it is able to biosynthesize it using ThiA; the tenA/thiA double mutant, however, is hydroxypyrimidine-requiring and is unable to salvage the pyrimidine from formylaminopyrimidine, aminopyrimidine, or base-degraded thiamine (PubMed:17618314). Belongs to the TenA family. Was originally described as a regulatory protein involved in the regulation of the production of extracellular enzymes.