Catalyzes the hydrolysis of glutamine to glutamate and ammonia as part of the biosynthesis of pyridoxal 5'-phosphate. The resulting ammonia molecule is channeled to the active site of PdxS. aldehydo-D-ribose 5-phosphate + D-glyceraldehyde 3-phosphate + L-glutamine = H(+) + 3 H2O + L-glutamate + phosphate + pyridoxal 5'-phosphate H2O + L-glutamine = L-glutamate + NH4(+) Cofactor biosynthesis; pyridoxal 5'-phosphate biosynthesis. In the presence of PdxS, forms a dodecamer of heterodimers. Only shows activity in the heterodimer. Belongs to the glutaminase PdxT/SNO family.