SOFTWOOD HEMICELLULOSE-DEGRADING ENZYMES FROM ASPERGILLUS-NIGER - PURIFICATION AND PROPERTIES OF A BETA-MANNANASE

The enzymes needed for galactomannan hydrolysis, i.e. beta-mannanase, alpha-galactosidase and beta-mannosidase, were produced by the filamen tous fungus Aspergillus niger. The beta-mannanase was purified to elec trophoretic homogeneity in three steps using ammonium sulfate precipit ation, anion-exchange chromatography and gel filtration. The purified enzyme had an isoelectric point of 3.7 and a molecular mass of 40 kDa. Ivory nut mannan was degraded mainly to mannobiose and mannotriose wh en incubated with the beta-mannanase. Analysis by H-1 NMR spectroscopy during hydrolysis of mannopentaose showed that the enzyme acts by the retaining mechanism. The N-terminus of the purified A. niger beta-man nanase was sequenced by Edman degradation, and comparison with Aspergi llus aculeatus beta-mannanase indicated high identity. The enzyme most probably lacks a cellulose binding domain since it was unable to adso rb on cellulose. (C) 1998 Elsevier Science B.V. All rights reserved.