Purification and properties of a cellulase from Aspergillus niger

Abstract

A cellulolytic enzyme was isolated from a commercial cellulase preparation from A. niger. A yield of about 50 mg of enzyme was obtained per 100 g of commercial cellulase. The isolated enzyme was homogeneous in ultracentrifuge at pH 4.0 and 8.0, and in sodium dodecyl sulfate/polyacrylamide-gel electrophoresis but showed 1 major and 2 minor bands in disc gel electrophoresis. No carbodhydrate was associated with the protein. Amino acid analysis revealed that the enzyme was rich in acidic and aromatic amino acids. Data from amino acid composition and dodecyl sulfate/polyacrylamide-gel electrophoresis indicated a MW of 26,000. The purified enzyme was active towards CM[carboxymethyl]-cellulose, but no activity towards cellobiose or p-nitrophenyl .beta.-D-glucoside was detected under assay conditions used. The pH optimum for the enzyme was pH 3.8-4.0, and it was stable at 25.degree. C over the range pH 1-9; maximum activity (at pH 4.0) was obtained at 45.degree. C. The cellulase was more stable to heat treatment at pH 8.0 than at 4.0. Kinetic studies gave pK values between 4.2 and 5.3 for groups involved in the enzyme-substrate complex.