May play a role in neurotransmitter secretion. Predominantly cytosolic. Also exists as a membrane-bound form which has been found associated with synaptic vesicles and also with the Golgi complex and immature secretory granules. Additional isoforms seem to exist. Predominantly expressed in brain, pancreas and stomach mucosa. High expression also found in stomach muscle and testis. 129/SvJ mice lacking Ica1 do not display an obvious phenotype and age normally, while NOD mice without Ica1 develop diabetes and display sudden mid-life lethality but are resistant to cyclophosphamide-induced disease acceleration.