Catalyzes the first reaction in the primary pathway for the renal catabolism of glutamine. Plays a role in maintaining acid-base homeostasis. Regulates the levels of the neurotransmitter glutamate in the brain. Isoform 2 lacks catalytic activity. Isoform 1 and isoform 3 are activated by phosphate. Inhibited by BPTES. BPTES binds between subunits and favors dissociation of the tetramer into dimers.