Purification and characterization of an endo-β-(1→6)-galactanase from Trichoderma viride

Abstract

An endo-β-(1→6)-galactanase from Onozuka R-10, a commercial cellulase preparation from Trichoderma viride, was purified 57-fold. Apparent M r values of the purified enzyme, estimated by denaturing gel electrophoresis and gel filtration, were 47,000 and 17,000, respectively. The enzyme was assayed with a galactan from Prototheca zopfii, which has a high proportion of β-(1→6)-linked galactosyl residues . It exhibited maximal activity toward the galactan at pH 4.3. The enzyme hydrolyzed specifically β-(1→6)-galactooligosaccharides with a degree of polymerization higher than 3 and their acidic derivatives with 4- O-methyl-glucosyluronic or glucosyluronic groups at the nonreducing terminals. The methyl β-glycoside of β-(1→6)-galactohexaose was degraded to reducing galactooligomers with a degree of polymerization 2–5 as the products at the initial stage of hydrolysis, and galactose and galactobiose at the final stage, indicating that the enzyme can be classified as an endo-galactanase. The extent of hydrolysis of the carbohydrate portion of a radish root arabinogalactan-protein (AGP) increased when α- l-arabinofuranosyl residues attached to β-(1→6)-linked galactosyl side chains of the AGP were removed in advance. The enzyme released galactose, β-(1→6)-galactobiose, and 4- O-methyl-β-glucuronosyl-(1→6)-galactose as major hydrolysis products when allowed to act exhaustively on the modified AGP.