ATP-dependent low-affinity peptide transporter which translocates a broad spectrum of peptides from the cytosol to the lysosomal lumen for degradation. Displays a broad peptide length specificity from 6-mer up to at least 59-mer peptides with an optimum of 23-mers. Binds and transports smaller and larger peptides with the same affinity. Favors positively charged, aromatic or hydrophobic residues in the N- and C-terminal positions whereas negatively charged residues as well as asparagine and methionine are not favored. a [oligopeptide](in) + ATP + H2O = a [oligopeptide](out) + ADP + H(+) + phosphate Homodimer. Interacts (via TMD0 region) with LAMP1; this interaction strongly stabilizes ABCB9 and protects ABCB9 against lysosomal degradation. Interacts (via TMD0 region) with LAMP2 (isoform LAMP-2B). Interacts (via TMD0) with YIF1B; this interaction allows (but is not essential) the ER-to-Golgi trafficking and strongly depends on a salt bridge within TMD0. May be located in membrane rafts. Takes an intracellular route from the endoplasmic reticulum (ER), via Golgi and early endosomes to late endosomal and lysosomal compartments. Highly expressed in testis, particularly in the Sertoli cells of the seminiferous tubules, and at moderate levels in brain and spinal cord. Divided into an N-terminal domain (TMD0) comprising four transmembrane helices and the following core domain (coreABCB9). TMD0 is required for lysosomal localization and LAMP1, LAMP2 and YIF1B interaction. The core domain is required for homodimerization and peptide transport activity. Belongs to the ABC transporter superfamily. ABCB family. MHC peptide exporter (TC 3.A.1.209) subfamily. Extended N-terminus.