The kinetics of cellulose enzymatic hydrolysis: Implications of the synergism between enzymes

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…


1. Introduction
1.1 The substrate: Cellulose
1.2 The enzymes: Cellulases
1.3 Trichoderma reesei cellulases
1.3.1 CBH I (Cel7A)
1.3.2 CBH II (Cel6A)
1.3.3 Endoglucanases
1.4 Enzymatic hydrolysis of cellulose: synergism between enzyme components
1.5 Kinetics of cellulose hydrolysis
1.6 Adsorption of cellulase to cellulose: the roles and function of cellulose-binding domains (CBD-s)
1.7 Possible applications of cellulases
2. Purposes of the study
3. Present investigation
3.1 Materials and assays
3.1.1 Cellulose substrates
3.1.2 Cellulases
3.1.3 Hydrolysis kinetics
3.1.4 Analytical procedures
3.2 Results and discussion
3.2.1 Hydrolysis kinetics, individual enzymes
3.2.2 Synergism between cellulases
3.2.3 Diffusion limitations, fractal like kinetics
3.2.4 Inhibition of cellulases by cellobiose
4. Conclusions
5. Acknowledgement
6. References

Author: Väljamäe, Priit

Source: Uppsala University Library

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