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

• Compound ID: 26096
  

  b-D-Galp-(1-6)-+ | -3)-b-D-Galp-(1-3)-b-D-Galp-(1-3)-b-D-Galp-(1-3)-b-D-Galp-(1-3)-b-D-Galp-(1-3)-b-D-Galp-(1-

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  Structure type: polymer chemical repeating unit
  Reference(s) to other database(s): GTC:G74464ZI, CCSD:34631, CBank-STR:18548
  
   
  
  Acacia senegal
  CSDB ID 118237 (all data & tools)
• Compound ID: 26097
  

  a-L-Araf-(1-3)-b-D-Galp-(1-6)-D-Galp

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  Structure type: oligomer
  Reference(s) to other database(s): GTC:G37168BU, CCSD:34632, CBank-STR:4792
  
   
  
  Acacia senegal
  CSDB ID 118238 (all data & tools)