A novel tannase from Aspergillus niger with β-glucosidase activity

Abstract

An extracellular tannase was produced from solid-state cultures of Aspergillus niger. The enzyme was purified to homogeneity from the cell-free culture broth by preparative isoelectric focusing and by FPLC using anion-exchange and gel-filtration chromatography. SDS-PAGE analysis as well as gel localization studies of purified tannase indicated the presence of two enzyme forms, with molecular masses of 90 kDa and 180 kDa. The tannase had an isoelectric point of 3·8, a temperature optimum of 60–70 °C and a pH optimum of 6·0. The substrate specificity of the tannase was determined by HPLC analysis of tannin substrates and products. The enzyme was able to remove gallic acid from both condensed and hydrolysable tannins. Internal sequences were obtained from each of the gel-purified and trypsin-digested tannase forms. The peptide sequences obtained from both forms were identical to sequences within a β-glucosidase from Aspergillus kawachii. The purified tannase was tested for β-glucosidase activity and was shown to hydrolyse cellobiose efficiently. However, no β-glucosidase activity was detected when the enzyme was assayed in the presence of tannic acid.