title: Inhibition of enzymatic hydrolysis by residual lignins from softwood--study of enzyme binding and inactivation on lignin-rich surface.
abstract: Lignin-derived inhibition is a major obstacle restricting the enzymatic hydrolysis of cell wall polysaccharides especially with softwood lignocellulosics. Enzyme adsorption on lignin is suggested to contribute to the inhibitory effect of lignin. The interaction of cellulases with softwood lignin was studied in the present work with commercial Trichoderma reesei cellulases (Celluclast) and lignin-rich residues isolated from steam pretreated softwood (SPS) by enzymatic and acid hydrolysis. Both lignin preparations inhibited the hydrolysis of microcrystalline cellulose (Avicel) and adsorbed the major cellulases present in the commercial cellulase mixture. The adsorption phenomenon was studied at low temperature (4°C) and at the typical hydrolysis temperature (45°C) by following activities of free and lignin-bound enzymes. Severe inactivation of the lignin-bound enzymes was observed at 45°C, however at 4°C the enzymes retained well their activity. Furthermore, SDS-PAGE analysis of the lignin-bound enzymes indicated that very strong interactions form between the residue and the enzymes at 45°C, because the enzymes were not released from the residue in the electrophoresis. These results suggest that heat-induced denaturation may take place on the surface of softwood lignin at the hydrolysis temperature.
authors.affiliation: VTT Technical Research Centre of Finland, PO Box 1000, 02044 VTT, Finland.
authors.forename: Jenni
authors.initials: J
authors.lastname: Rahikainen
authors.forename: Saara
authors.initials: S
authors.lastname: Mikander
authors.forename: Kaisa
authors.initials: K
authors.lastname: Marjamaa
authors.forename: Tarja
authors.initials: T
authors.lastname: Tamminen
authors.forename: Angelos
authors.initials: A
authors.lastname: Lappas
authors.forename: Liisa
authors.initials: L
authors.lastname: Viikari
authors.forename: Kristiina
authors.initials: K
authors.lastname: Kruus
mesh_terms: D044602:Cellulases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D024202:Electrophoretic Mobility Shift Assay; D004791:Enzyme Inhibitors / Q000378:metabolism*; D006868:Hydrolysis; D008031:Lignin / Q000378:metabolism*; D011134:Polysaccharides / Q000378:metabolism*; D013696:Temperature; D014242:Trichoderma / Q000201:enzymology*; D014934:Wood / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D011134:Polysaccharides; D008031:Lignin; D044602:Cellulases