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Mode of action of exoglucanases from the cellulolytic fungus Trichoderma reesei: activity on reducing end-labeled cellooligosaccharides and topography of active sites of. beta. -glucosidase, cellobiohydrolase I(D), and cellobiohydrolase II

Thesis/Dissertation ·
OSTI ID:5941959
The activity of purified ..beta..-glucosidase, cellobiohydrolase I(D) and cellobiohydrolase II from Trichoderma reesei was studied using (1-/sup 3/H)cellooligosaccharides. Reducing end-labeled cellooligosaccharides of high specific radioactivity were synthesized by reducing lactones of cellooligosaccharide aldonic acids with sodium boro(/sup 3/He)hydride. A thin-layer chromatographic method for separating (1-/sup 3/H)cellooligosaccharides with high resolution and quantitatively extracting them from silica gel was developed. The ..beta..-glucosidase was shown to bind (1-/sup 3/H)cellooligosaccharides in one productive mode and sequentially remove glucosyl residues from the nonreducing end. Cellobiohydrolase I(D) was shown to bind (1-/sup 3/H)cellooligosaccharides in more than one productive mode. Cellobiohydrolase II was also shown to bind (1-3H) cellooligosaccharides in more than one productive model; however, glycosidic bonds at the nonreducing end are preferentially hydrolyzed. The results are discussed in terms of the individual roles of exoglucanases during the saccharification of cellulose. A mechanism by which cellobiohydrolase I(D) and cellobiohydrolase II may synergistically degrade crystalline cellulose is proposed.
Research Organization:
Florida Univ., Gainesville (USA)
OSTI ID:
5941959
Country of Publication:
United States
Language:
English