Involved in the degradation of arabinan and is a key enzyme in the complete degradation of the plant cell wall. Catalyzes the cleavage of terminal alpha-(1->5)-arabinofuranosyl bonds in different hemicellulosic homopolysaccharides (branched and debranched arabinans). It acts preferentially on aryl-alpha-L-arabinofuranosides, and is much less effective on aryl-beta-D-xylopyranosides. Hydrolysis of terminal non-reducing alpha-L-arabinofuranoside residues in alpha-L-arabinosides. Strongly inhibited by Hg(2+). Apparently, AbfA can accommodate xylopyranose in the active site, but without the necessary distortion required for the efficient catalysis of six-membered rings. This explains in part its lower specificity towards the xylopyranosidic substrates (PubMed:14517232). Optimum pH is 5.5-6.0. Optimum temperature is 70 degrees Celsius. Glycan metabolism; L-arabinan degradation. Homohexamer; trimer of dimers. 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 (Probable). Belongs to the glycosyl hydrolase 51 family.