DEGRADATION OF ARABINANS BY ARABINANASES FROM ASPERGILLUS-ACULEATUS AND ASPERGILLUS-NIGER

An endo-arabinanase was purified from an enzyme preparation, derived from Aspergillus aculeatus. After SDS-gel electrophoresis a molecular weight of 45 kDa was estimated. The enzyme was reactive with antibodies raised against endo-arabinanase from Aspergillus niger, having the same molecular weight. Besides similarities, remarkable differences were observed for endo-arabinanases from A. niger and A. aculeatus. The enzyme from A. aculeatus was optimally active at a higher pH and produced a different spectrum of oligomers after incubation with linear arabinan. This was reflected in a relatively low concentration of oligomers with a degree of polymerization (DP) of 13 and a high concentration of oligomers with a DP of 6-7. Contrary to this, the concentration of oligomers produced by the A. niger endo-arabinanase gradually increased, going from DP 20 to DP 3. Both endo-arabinanases, as well as arabinofuranosidase B from A. niger, were studied with respect to the degradation of branched arabinans. Removal of arabinofuranosyl side chains by arabinofuranosidase B was essentially independent of the type of glycosidic linkage but had a tremendous effect on the digestibility by endo-arabinanase.