Involved in the degradation of arabinan and is a key enzyme in the complete degradation of the plant cell wall. Catalyzes the internal cleavage of alpha-(1->5)-L-arabinofuranosyl residues of debranched arabinan, linear arabinan and short arabino-oligosaccharides (degree of polymerization from 2 to 8). It exhibits marginal activity toward sugar beet arabinan. Endohydrolysis of (1->5)-alpha-arabinofuranosidic linkages in (1->5)-arabinans. Binds 1 Ca(2+) ion per subunit. Glycan metabolism; L-arabinan degradation. Monomer. Transcription is repressed by glucose and by the binding of AraR to the operon promoter. L-arabinose acts as an inducer by inhibiting the binding of AraR to the DNA, thus allowing expression of the gene. Belongs to the glycosyl hydrolase 43 family.