Swiss-Prot Acc.O94925.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.CautionIsoform 3 is predicted to be expressed at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay (PubMed:14759258), but has been shown to be well expressed (PubMed:17940881 and PubMed:11015561) and the encoded protein is detected in mitochondria (PubMed:22228304).