Characterization of Galactosidases from Aspergillus niger: Purification of a Novel α-Galactosidase Activity (original) (raw)

An enzyme with ␤-galactosidase activity and three proteins exhibiting ␣-galactosidase activity were purified from a culture filtrate of Aspergillus niger grown on arabinoxylan. ␤-galactosidase, optimally active at pH 4 and 60 -65°C, was active against p-nitrophenyl-␤-D-galactopyranoside, lactose, and pectic galactan. It was not able to release galactose from sugar beet pectin or lemon pectin. Its action on pectic galactan was increased by the presence of ␤-galactanase. The three forms of ␣-galactosidase activity that showed different molecular masses and pIs were found to have the same mass after deglycosylation with N-glycanase F and to be the same protein based on their N-terminal amino acid sequence data. The purified ␣-galactosidase was shown to be different from ␣-galactosidase A from A. niger. This confirmed the existence of at least two different ␣-galactosidases in A. niger. ␣-Galactosidase, optimally active at pH 4.5 and 50 -55°C, was active toward p-nitrophenyl-␣-Dgalactopyranoside, melibiose, raffinose, stachyose, and locust bean gum, on which substrate it exhibited synergism with ␤-mannanase.