Purification and characterization of an extracellular exo-D-galacturonanase of Aspergillus niger.

A D-galacturonanase (EC 3.2.1.67) catalyzing the degradation of D-galacturonans by terminal action pattern was purified from a culture filtrate of Aspergillus niger by a procedure including the salting-out with ammonium sulfate, precipitation by ethanol, chromatography on DEAE-cellulose, and gel chromatography on Sephadex G-100. The obtained preparation was slightly contaminated by an enzymically inactive protein fraction. Maximum activity and stability of the enzyme was observed at pH 5.2. The enzyme degrades digalacturonic acid, p-nitrophenyl-alpha-D-galactopyranuronide, as well as oligogalacturonides containing at the nonreducing end 4-deoxy-L-threo-hexa-4-enopyranosyluronate. It differs from all A. niger enzymes so far described which degrade D-galaturonans by the terminal action pattern, in not clearly preferring low-molecular substrates. It is therefore classified as an exo-D-galacturonanase.