An exo-(1→3)-β-d-galactanase was purified by six chromatographic steps from a culture supernatant of Aspergillus niger. Its apparent molecular mass was 66 kDa, as estimated by SDS-PAGE analysis. The purified enzyme had no detectable activity on various p-nitrophenyl glycosides and on native plant polysaccharides but exhibited a high activity on a (1→3)-β-d-linked galactan backbone obtained after partial acid hydrolysis and two Smith degradations of gum arabic. The optimum conditions were pH 4.5 and 40–50°C. The enzyme had a Michaelis constant (Km) of 1.9 mg/mL for the β-(1→3)-d-galactan with a maximum reaction velocity (Vmax) of 1380 nkat/mg. The study of the reaction products obtained after enzyme treatment of two galactans derived from gum arabic through one or two Smith degradations showed that it was an exo-(1→3)-β-d-galactanase able to by-pass the branching points of galactan backbones and thus to release the side-chains of type II arabinogalactans in an undegraded form.
arabinogalactan, Galactan, Aspergillus niger, galactanase, polysaccharide hydrolase
NCBI PubMed ID: 7805066Publication DOI: 10.1016/S0008-6215(05)80012-6Journal NLM ID: 0043535Publisher: Elsevier
Institutions: Institut National de la Recherche Agronomique, Laboratoire des Polymères et des Techniques Physico-Chimiques, Montpellier, France
Methods: gel filtration, GC-MS, acid hydrolysis, HPAEC, enzymatic digestion
Found