Adsorpton and Activity of Cellulase Enzymes on Various of Cellulose Substrates

Abstract

The objective of this research is to understand the interfacial behavior of cellulase enzymes and its effect on cellulose hydrolysis. This research began with an in-situ monitoring of cellulose hydrolysis using a piezoelectric based quartz crystal microbalance. The time-course kinetics was modeled using a dose response model. The adsorption indicated by the frequency drop followed a Langmuir model as cellulase enzyme increased. Another important part of this research is the development of a new cellulase activity assay based on the piezoelectric technique. This assay provides an easier and more user friendly method for cellulase enzyme activity measurement. It also helps to clarify an element of the interpretation of frequency drops after the injection of cellulase solutions in the hydrolysis of cellulose film, which has been neglected in previous research. Interfacial adsorption of cellulase protein was also investigated using the depletion method. The effects of substrate properties, primarily the crystallinity, which was characterized using X-ray diffraction, were investigated. The effect of surface area, which was measured using both laser light scattering and BET adsorption, on cellulase adsorption were also investigated. It was found that crystallinity played a more important role in cellulase adsorption than surface areas of cellulosic substrate. In characterization of cellulosic substrates, the water retention value (WRV) was also investigated. The results indicated that lower crystallintiy substrates have higher water retention ability. The cellulase adsorption, as well as desorption, was also studied by using sodium dodecyle sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The adsorption results followed the same trend as indicated by the depletion methods. The various isozymes demonstrated a uniform adsorption in proportion to their concentrations. Desorption appeared uniform. Higher pH was found to create higher desorption for a particular cellulase from a particular substrates. It was also found that cellulase from Trichoderma reesei had higher affinity to cellulosic substrates used in this work than the one from Aspergillus niger.