Purification and Properties of an Endo-Cellulase of Avicelase Type from Irpex lacteus (Polyporus tulipiferae)

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Abstract
A culture filtrate of Irpex lacteus (Polyporus tulipiferae) was fractionated initially by salting out with ammonium sulfate, and a cellulase [EC 3.2.1.4] fraction with high Avicel-hydrolyzing activity (formerly called Avicelase) was extensively purified by a series of column chromatography procedures. This purified endo-cellulase showed a less random hydrolytic mechanism, and was obtained in a yield of 0.04% with respect to the starting material. Its specific activity was enhanced approximately 30 times over that of the starting material. The cellulase component showed a single peak on both ultracentrifugal and acrylamide disc electrophoretic analyses. Its molecular weight was estimated to be 56, 000. It contained 12.2% carbohydrate; the major sugar constituents were glucose and mannose. Regarding the amino acid composition, the contents of aspartic acid and glycine were highest, followed by those of glutamic acid, serine, and threonine. The cellulase component was not markedly inhibited by most metal ions tested except for Hg2+. This purified endo-cellulase attacked a series of cellooligosaccharides, β-cellobioside, CM-cellulose, and insoluble cellulosic substrates. In the digests from insoluble substrates, glucose, cellobiose, cellotriose, and cellotetraose were detectable, but the amount of cellobiose was the largest by far. In contrast, cellobiose and glucose were produced in almost equal amounts from β-cellobioside.

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