Deconstruction by Enzymes 2: Hemicellulases Chun-Hung Lin Ph.D. 林 林 林 Institute of Biological Chemistry Academia Sinica E-mail: [email protected]
Jan 19, 2016
Deconstruction by Enzymes 2: Hemicellulases
Chun-Hung Lin Ph.D. 林 俊 宏Institute of Biological Chemistry
Academia Sinica
E-mail: [email protected]
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
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
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.
Monosaccharide Compositions andStereochemical Configuration
1. Glucose, Mannose, Galactose, Glucuronic acid, and
Galacturonic acid
2. Xylose, Arabinose
3. - and -linkage, anomeric center, reducing end
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
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.
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
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
Hemicellulose: A heterogeneous mixture of different polysaccahrides and compositions
Arabino-4-O-methylglucurono-xylan: a major component of
Softwoods (gymnosperms).
Hemicellulose: A heterogeneous mixture of different polysaccahrides and compositions
Acetyl-galacto-glucomannan: Another major component of softwoods