Induction, purification, and characterization of two extracellular alpha-L-arabinofuranosidases from Fusarium oxysporum

In the presence of L-arabinose as sole carbon source, Fusarium oxysporum produces two alpha-L-arabinofuranosidases (ABFs) named ABF1 and ABF2, with molecular masses of 200 and 180 kDa, respectively. The two F. oxysporum proteins have been purified to homogeneity. The purified enzymes are composed of three equal subunits and are neutral proteins with pIs of 6.0 and 7.3 for ABF1 and ABF2, respectively. With p-nitrophenyl alpha-L-arabinofuranoside (pNPA) as the substrate, ABF1 and ABF2 exhibited Km values of 0.39 and 0.28 mmol.L(-1), respectively, and Vmax values of 1.6 and 4.6 micromol.min(-1).(mg of protein)(-1), respectively, and displayed optimal activity at pH 6.0 and 50-60 degrees C. ABFs released arabinose only from sugar beet arabinan and not from wheat soluble and insoluble arabinoxylans. The enzymes were not active on substrates containing ferulic acid ester linked to C-5 and C-2 linkages of pNPA showing that phenolic substituents of pNPA sterically hindered the action of ABFs.