Part of the AP-3 complex, an adaptor-related complex which is not clathrin-associated. The complex is associated with the Golgi region as well as more peripheral structures. It facilitates the budding of vesicles from the Golgi membrane and may be directly involved in trafficking to the vacuole. Required for the transport via the ALP pathway, which directs the transport of the cargo proteins PHO8 and VAM3 to the vacuole. Adaptor protein complex 3 (AP-3) is a heterotetramer composed of 2 large adaptins (APL5 and APL6), a medium adaptin (APM3) and a small adaptin (APS3). Component of the coat surrounding the cytoplasmic face of coated vesicles located at the Golgi complex. Pyrophosphorylated by 5-diphosphoinositol pentakisphosphate (5-IP7) (PubMed:17873058). Serine pyrophosphorylation is achieved by Mg(2+)-dependent, but enzyme independent transfer of a beta-phosphate from a inositol pyrophosphate to a pre-phosphorylated serine residue (PubMed:17873058). Present with 3570 molecules/cell in log phase SD medium. Belongs to the adaptor complexes large subunit family.