Strongly inhibits glucose induced insulin release from the pancreas. Completely inhibits catecholamine release from chromaffin cells. Has antibacterial activity against M.luteus. Not active against E.coli. Inhibits catecholamine release from chromaffin cells and noradrenergic neurons by acting as a non-competitive nicotinic cholinergic antagonist (PubMed:9294131 and PubMed:9786174). Displays antibacterial activity against Gram-positive bacteria M.luteus and B.megaterium, and Gram-negative bacteria E.coli, and antifungal activity against a variety of filamentous fungi including A.fumigatus, N.hematococca, F.culmorum, F.oxyporum, T. mentagrophytes and several forms of Candida: C.albicans, C.tropicalis, C.glabrata and C.neoform (PubMed:15723172). Can induce mast cell migration, degranulation and production of cytokines and chemokines (By similarity). Has antibacterial activity against Gram-positive bacteria M.luteus, B.megaterium. Not active against Gram-positive bacteria B.cereus, B.subtilis, S.pyogenes, M.fortuitum, S.aureus and L.monocytogenes and against Gram-negative bacteria E.coli, E.cloacae, S.typhimurium, K.pneumoniae and P.aeruginosa. Possesses antifungal activity against N.crassa, A.fumigatus, A.brassicicola, N.hematococca, F.culmorum and F.oxyporum and against the yeast S.cerevisiae and C.albicans. Inactive against A.benhamiae. Has antifungal activity against N.crassa, A.fumigatus, A.brassicicola, N.hematococca, F.culmorum, F.oxyporum, A.benhamiae, C.neoformans, as well as against yeasts C.albicans, and C.tropicalis. Seems to be inactive against C.glabrata. Interacts with the fungal cell wall, crosses the plasma membrane and accumulates in fungal cells where it inhibits calcineurin activity. Regulates granule biogenesis in endocrine cells by up-regulating the transcription of protease nexin 1 (SERPINE2) via a cAMP-PKA-SP1 pathway. This leads to inhibition of granule protein degradation in the Golgi complex which in turn promotes granule formation (PubMed:21436258). Interacts with SCG3. Pyroglutaminated serpinin localizes to secretory vesicle. Associated with the secretory granule membrane through direct interaction to SCG3 that in turn binds to cholesterol-enriched lipid rafts in intragranular conditions. In pituitary gonadotropes, located in large secretory granules. Highest concentration of GE-25 found in adrenal medulla with lower levels present in the pituitary, the intestinal mucosa and the pancreas. Also found in the brain. In secretory granules, is attacked at both N- and C-terminal sides by proteolytic enzymes generating numerous peptides of various activities. Proteolytic processing can give rise to additional longer forms of catestatin peptides which display a less potent catecholamine release-inhibitory activity (PubMed:10781584). Binds calcium with a low-affinity. Belongs to the chromogranin/secretogranin protein family.