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 linear 1,5-alpha-L-arabinan and of branched sugar beet arabinan. It displays no activity against heavily substituted arabinans or a range of other polysaccharides (larch wood arabinogalactan, wheat arabinoxylan and p-nitrophenyl-alpha-L-arabinofuranoside). The enzyme activity is progressively reduced as alpha-(1->5)-chains become shorter or more highly substituted. Endohydrolysis of (1->5)-alpha-arabinofuranosidic linkages in (1->5)-arabinans. Binds 1 Ca(2+) ion per subunit. Optimum pH is 6.0. At pH 4.0 the arabinosidase retains about 8% of activity. Optimum temperature is 60 degrees Celsius. At 80 degrees Celsius retains about 2% of activity. Glycan metabolism; L-arabinan degradation. Induced by arabinose and arabina,n and repressed by glucose. Cells lacking this gene retains about 40% of the capacity to hydrolyze linear arabinan compared to the wild-type. Belongs to the glycosyl hydrolase 43 family.