Involved in the degradation of arabinan and is a key enzyme in the complete degradation of the plant cell wall. Catalyzes the cleavage of the terminal alpha-(1->5)-arabinofuranosyl bonds of linear arabinan and carboxymethylarabinan to produce almost exclusively arabinotriose. Hydrolysis of terminal non-reducing alpha-L-arabinofuranoside residues in alpha-L-arabinosides. kcat is 17.1 sec(-1) for arabinan. kcat is 212 sec(-1) for carboxymethylarabinan. Glycan metabolism; L-arabinan degradation. Homodimer. Induced by arabinan and repressed by glucose. The relative activity of the enzyme against the arabino-oligosaccharides increases with the increasing size of the substrate up to arabinohexaose, after which the rate remains constant. The substrate-binding site accommodates six arabinose units, with cleavage occurring between binding sites 3 and 4 (PubMed:9163351). Belongs to the glycosyl hydrolase 43 family.