Purification and properties of a lower-molecular-weight endo-cellulase from Irpex lacteus (Polyporus tulipiferae)

A new endo-cellulase component of carboxymethyl cellulase (CMCase) type (En-1) was obtained by gel filtration and column chromatography from Driselase, a commerical enzyme preparation from Irpex lacteus (Polyporus tulipiferae). The enzyme behaved as a single protein on polyacrylamide disc electrophoresis in the presence of sodium dodecyl sulfate (SDS). Its molecular weight was estimated to be 15,500 and it contained only 0.73% carbohydrate as glucose. The pattern of its amino acid composition is similar to those of other cellulases in respect of high contents of acidic amino acids, glycine, serine, and threonine. The cellulase was most active at pH 4.0 and was very stable in the pH range of 3.0 to 6.0, but was completely inactivated by heating at 70 degrees C for 10 min. A series of cellooligosacharides, including cellobiose, was formed by this enzyme from sodium carboxymethyl cellulose (CMC) as well as from water-insoluble celluloses. In the hydrolysis of CMC, the increase in the fluidity of the substrate was relatively large as compared with the simultaneous increase in reducing power. From this result and the pattern of hydrolysis products, En-1 was elucidated to be an endo-cellulase, and it showed the highest randomness among the cellulase components obtained so far from Irpex lacteus.