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J. Biochem, 1993, Vol. 114, No. 2 236-245
© 1993 Japanese Biochemical Society

other

Electron Microscopic Observation of Cotton Cellulose Degradation by Exo- and Endo-Type Cellulases from Irpex lacteus

Eiichi Hoshino*, Yasushi Sasaki*, Kazuo Mori**, Mituo Okazaki***, kazutosi Nisizawa****,1 and Takahisa Kanda*

*Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University Wakasato, Nagano, Nagano 380
**Household Products Research Laboratories, Kao Corporation Minato, Wakayama, Wakayama 640
***Department of Applied Biology, Faculty of Textile Science and Technology, Shinshu University Tokida, Ueda, Nagano 386
****Department of Fisheries, College of Agriculture and Veterinary Medicine, Nihon University Setagaya-ku, Tokyo 154

The interaction of two highly purified cellulases, exo- and endo-type cellulases from Irpex lacteus, with pure cotton and amorphous cellulose was investigated by electron microscopy. The morphological observations indicated that exo- and endo-type cellulases are both strongly adsorbed on the internal microfibril of cotton fiber before enzymatic hydrolysis, and then initiate their action toward the internal cellulose microfibrils with retention of the original shape. The two cellulases, however, caused considerably different morphological changes in cotton cellulose, and each cellulase seems to degrade native cellulose with a distinct mode of action. In the hydrolysis of cotton with exo-type cellulase, deep transverse cracks were produced and they extended from the fiber surface to the lumen structure located inside the fibers. In contrast, it was found that there were no deep cracks on fibers treated with endo-type cellulase, but severe internal erosion and cavitation occurred along fibril or microfibril layers inside the fibers. Thus, the degradation of cotton by exo- and endo-type cellulases yielded quite different morphological patterns, while little difference was found for regenerated celluloses. The mode of enzymatic hydrolysis of cellulose shown by cellulases with different degrees of randomness (exo and endo types) appears to be markedly affected by the fine structure of cellulose fibers.

1Present address: 10-ban-4, Kouyama-3, Nerima-ku, Tokyo 176.


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