Purification and Properties of an Exo-Cellulase of Avicelase Type from a Wood-Rotting Fungus, Irpex lacteus (Polyporus tulipiferae)

Abstract

A cellulase component of Avicelase type was obtained from Driselase, a commercial enzyme preparation from a wood-rotting fungus Irpex lacteus (Polyporus tulipiferae). It showed a single band on SDS-polyacrylamide electrophoresis. The amino acid composition of this cellulase resembled those of cellulase components of endo-type from the same fungus. However, it produced exclusively cellobiose from CMC as well as from water-insoluble celluloses such as Avicel or cotton at earlier stages of hydrolysis. In addition, the hydrolysis of CMC practically stopped after an initial rapid stage. The cellulase showed a strong syner-gistic action with an endo-cellulase of higher randomness (typical CMCase-type) in the hydrolysis of CMC as well as Avicel. In contrast to cellotriose and -tetraose, cellopentaose and -hexaose were attacked very rapidly, and only cellobiose was produced. These results suggest that the cellulase is an exo-type component. However, it mutarotated the products from cellopentaitol in the same direction as endo-cellulases. It represented a relatively large portion of the total cellulase activity, and may play an important role in the degradation of native cellulose in vivo.