Adsorption of Clostridium thermocellum cellulases onto pretreated mixed hardwood, avicel, and lignin

Abstract

Adsorption of Avicel-hydrolyzing activity was examined with respect to: mixed hardwood flour pretreated with 1% sulfuric acid for 9 s at 220°C (PTW220), lignin prepared from PTW220 by either acid or enzymatic hydrolysis, and Avicel. Experiments were conducted at 60°C for all materials, and also at 25°C for PTW220. Based on transient adsorption results and reaction rates, times were selected at which to characterize adsorption at 60°C as follows: PTW220, 1 min; lignin, 30 min; and Avicel, 45 min. Similar results were obtained for adsorption of cellulase activity to PTW220 at 25 and 60°C, and for lignin prepared by enzymatic and acid hydrolysis. For all materials, adsorption was described well by a Langmuir equation, although the reversibility of adsorption was not investigated. Langmuir affinity constants (L/g) were: PTW220, 109; lignin, 17.9; Avicel, 4.3; cellulose from PTW220, ≥187. Langmuir capacity constants were 760 for PTW220 and 42 for Avicel; the cellulase binding capacity of lignin appeared to be very high under the conditions examined, and could not be determined. At low and moderate cellulase loadings at least, the majority of cellulase activity adsorbed to PTW220 is bound to the cellulosic component. The results indicate that PTW220, and its cellulose component in particular, differ radically from Avicel with respect to adsorption. Avicel-hydrolyzing activity and CMC-hydrolyzing activities were found to bind to Avicel with a constant ratio of essentially one, consistent with adsorption of a multi-activity complex. © 1993 John Wiley & Sons, Inc.