An extracellular β-galactofuranosidase from Aspergillus niger and its use as a tool for glycoconjugate analysis

Aspergillus niger produces an extracellular beta -galactofuranosidase, which can specifically hydrolyse beta -D-galactofuranose (Galf) from glycoconjugates. The production of this enzyme can be induced by the addition of a Galf-containing A. niger mycelial wall extract. However, on other carbon sources accumulation occurred only during the starvation conditions of the late stationary phase. Extracellular glucoamylases from this stage of cultivation possessed significantly lower levels of Galf than those from the earlier exponential growth phase when beta -galactofuranosidase is absent, suggesting in situ beta -galactofuranosidic hydrolysis. The beta -galactofuranosidase responsible was subsequently purified to homogeneity and characterised. It is a glycoprotein of 90 kDa (determined by SDS-PAGE) with activity against beta -linked Galf residues. with a K(m) of 4 mM against p-nitrophenyl-beta -o-galactofuranoside and a pH optimum of 3-4. The preparation did not contain other contaminating glycosidase activities; p-nitrophenyl-beta -D- and -alpha -D-galactopyranose, and alpha -D-methyl-Galf were not hydrolysed. Results are presented to show that this enzyme could be employed as a useful tool for the analysis of glycoconjugates containing biologically important Galf components. (C) 2001 Elsevier Science B.V. All rights reserved.