Antizyme inhibitor (AZI) protein that positively regulates ornithine decarboxylase (ODC) activity and polyamine uptake. AZI is an enzymatically inactive ODC homolog that counteracts the negative effect of ODC antizyme (AZ) on ODC activity by competing with ODC for antizyme-binding. Inhibits antizyme-dependent ODC degradation and releases ODC monomers from their inactive complex with antizymes, leading to formation of the catalytically active ODC homodimer and restoring polyamine production. Participates in the morphological integrity of the trans-Golgi network (TGN) and functions as a regulator of intracellular secretory vesicle trafficking. Monomer. Interacts with OAZ1; this interaction disrupts the interaction between the antizyme and ODC1. Does not form a heterodimer with ODC1. Expression is first detected at the animal pole at stage 9. During neurula stages it is found both in the extreme anterior and posterior part of the dorsal body axis. In tailbud stages the expression is further shifted to both the tail and head areas and gradually restricted to distinct tissues: forebrain, inner layer of epidermis of the head area, stomodeal-hypophyseal anlage, frontal gland, ear vesicle, branchial arches, the front tip of neural tube and proctodeum. The N-terminus domain is necessary for its localization to the ER-Golgi intermediate compartment (ERGIC). Belongs to the Orn/Lys/Arg decarboxylase class-II family. ODC antizyme inhibitor subfamily. Human ortholog was initially reported to have ornithine decarboxylase or arginine decarboxylase activities, but it was later found that the mouse ortholog does not possess either of them.