Studies on Cellulases of a Phytopathogenic Fungus, Pyricularia oryzae Cavara

Abstract

Three components (GA, GB-1, and GB-2) of β-glucosidase were detected in the culture filtrate of Pyricularia oryzae grown in a cellulose or cellulose derivative medium. Among them, GB-1 was induced most strongly. Purified GB-1 was homogeneous on polyacrylamide gel electrophoresis and showed an approximately 1,400-fold increase of specific activity over the starting material. The molecular weight was determined to be 240,000 by sodium dodecyl sulfate-gel electrophoresis. A similar value was also obtained by sucrose density gradient centrifugation. The enzyme contained a high proportion of acidic amino acids and mannose, and the isoelectric point of the enzyme was pH 4.15. The enzyme had a pH optimum of 5.5 and a temperature optimum at 55°C. β-Gluco-sidase activity was inhibited by Mn²⁺, Cu²⁺, Hg²⁺, p-chloromercuribenzoate, and glucono-δ-lactone. The enzyme split off glucose units one by one from the nonreducing ends of not only β-glucooligosaccharides but also some β-glucans, such as carboxymethylcellulose, lami-naran, pustulan, and zeagallan. The affinity for cello- and laminari-oligosaccharides tended to increase in parallel with the chain length.