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 the alpha-1,5-L-arabinan to produce arabino-oligosaccharides and L-arabinose. It is also active toward linear branched sugar beet arabinan, and pectin from apple. Endohydrolysis of (1->5)-alpha-arabinofuranosidic linkages in (1->5)-arabinans. Binds 1 Ca(2+) ion per subunit. Optimum pH is 7. Optimum temperature is 50 degrees Celsius. It remains fully active after 30 minutes of preincubation at 50 degrees Celsius, however, after preincubation at 60 degrees Celsius, the residual activity is only 15%. Glycan metabolism; L-arabinan degradation. Homodimer. Repressed by glucose, and induced by pectin and arabinan. No visible phenotype. Double mutant abn2/abnA induce an almost complete loss of this activity. Belongs to the glycosyl hydrolase 43 family.