1. Deconstruction by Enzymes 2: Hemicellulases Chun-Hung Lin Ph.D. 林 俊 宏 Institute of Biological Chemistry Academia Sinica E-mail: chunhung@gate.sinica.edu.tw

2. Degradation of Hemicellulose Knowledge offered to you includes (1) What is hemicellulose? (2) Why is ligno-cellulose considered to be a renewable alternative to fossil fuels? (3) What enzymes are involved in hemicellulose degradation? (4) General aspects, e.g. catalytic mechanism, synergistic effect, how to reduce the enzyme cost, a suitable process for biofuel production

3. Chemical Compositions of Biomass 1.Heterogeneous compositions 2.The composition varies among species 3.In average, biomass consists of ~25% lignin and ~75% carbohydrate polymers (cellulose and hemicellulose) 4.Structures of cellulose and hemicellulose

7. The carbohydrate fraction is made of primarily of glucose; however, the pentose fraction is rather significant. Xylose is second only to glucose in natural abundance and it is the most copious sugar in the hemicellulose of hardwoods and crop residues.

8. Structure of Cellulose Glucose-  1,4-linked polymer

9. Monosaccharide Compositions and Stereochemical Configuration 1.Glucose, Mannose, Galactose, Glucuronic acid, and Galacturonic acid 2.Xylose, Arabinose  - and  -linkage, anomeric center, reducing end

10. Hexose and Pentose

15. Glucose-  1,4-linked polymer

18. Structure of Hemicellulose

19. Difference between Cellulose and Hemicellulose 1.Different compositions 2.Degree of polymerization (DP) Cellulose: DP varies from 2000 to 15000 Hemicellulose: DP varies from 100 to 200

20. Hemicellulose: A heterogeneous mixture of different polysaccahrides and compositions Xyloglucan: the predominant hemicellulose. It coats the surface of the cellulose microfibrils, limiting their aggregation and connecting them via tethers for the mechanical properties.

21. Hemicellulose: A heterogeneous mixture of different polysaccahrides and compositions  -1,3-1,4-Glucan: associated with cellulose microfibrils in the primary cell wall of grasses

22. Hemicellulose: A heterogeneous mixture of different polysaccahrides and compositions O-Acetyl-4-O-methyl-glucurono-xylan: Existing as the primary walls of grasses and secondary walls of all angiosperms (hardwoods). It is the most common building block in hardwoods

24. Hemicellulose: A heterogeneous mixture of different polysaccahrides and compositions Arabino-4-O-methylglucurono-xylan: a major component of Softwoods (gymnosperms).

25. Hemicellulose: A heterogeneous mixture of different polysaccahrides and compositions Acetyl-galacto-glucomannan: Another major component of softwoods

26. Enzymes involved in the degradation of hemicellulose

28. Catalytic Reaction Mechanism

29. Synergistic Effect