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The kinetics of cellulose enzymatic hydrolysis: Implications of the synergism between enzymes
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Biochemistry.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The hydrolysis kinetics of bacterial cellulose and its derivatives by Trichoderma reesei cellulases was studied. The cellulose surface erosion model was introduced to explain the gradual and strong retardation of the rate of enzymatic hydrolysis of cellulose. This model identifies the decrease in apparent processivity of cellobiohydrolases during the hydrolysis as a major contributor to the decreased rates. Both enzyme-related (non-productive binding) and substrate-related (erosion of cellulose surface) processes contribute to the decrease in apparent processivity. Furthermore, the surface erosion model allows, in addition to conventional endo-exo synergism, the possibility for different modes of synergistic action between cellulases. The second mode of synergism operates in parallel with the conventional one and was found to be predominant in the hydrolysis of more crystalline celluloses and also in the synergistic action of two cellobiohydrolases.

A mechanism of substrate inhibition in synergistic hydrolysis of bacterial cellulose was proposed whereby the inhibition is a result of surface dilution of reaction components (bound cellobiohydrolase and cellulose chain ends) at lower enzyme-to-substrate ratios.

The inhibition of cellulases by the hydrolysis product, cellobiose, was found to be strongly dependent on the nature of the substrate. The hydrolysis of a low molecular weight model substrate, such as para-nitrophenyl cellobioside, by cellobiohydrolase I is strongly inhibited by cellobiose with a competitive inhibition constant around 20 μM, whereas the hydrolysis of cellulose is more resistant to inhibition with an apparent inhibition constant around 1.5 mM for cellobiose.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2002. , p. 54
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 781
Keywords [en]
Biochemistry, Acetobacter, Cellobiohydrolase, Cellobiose, Cellulase, Cellulose, Diffusion, Endoglucanase, Hydrolysis, Inhibition, Kinetics, Model, Product, Substrate, Surface, Synergism, Trichoderma reesei
Keywords [sv]
Biokemi
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:uu:diva-3120ISBN: 91-554-5479-8 (print)OAI: oai:DiVA.org:uu-3120DiVA, id: diva2:162227
Public defence
2002-12-20, Lecture hall B21, Biomedical Center, Uppsala, 10:15
Opponent
Available from: 2002-11-28 Created: 2002-11-28Bibliographically approved

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