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Abstract
Bioconversion of cellulose has great potential for applying large quantities of fermentable feedstocks which can be converted to fuels and commodity chemicals. To achieve maximum conversion of celluose in enzymatic hydrolysis processes, characteristics of enzyme components comprising the cellulase enzyme system must be defined. Some of the most important characteristics to be defined are the synergistic interactions among the various components comprising the system. The goal of this research was to investigate synergism among component enzymes from various sources in order to enhance overall activity in enzymatic hydrolysis processes.
Simple purification procedures were developed to obtain electrophoretically homogeneous enzyme components. Commercial cellulases from Trichoderma viride, Penicillium funiculosum, and Aspergillus niger were purified using gel filtration followed by chromatofocusing. In some cases, chromatofocusing fractions were further purified by a second gel filtration step. Selected enzymes components were characterized for molecular weight, optimum pH and inhibition by glucose and cellobiose.
Synergistic interactions were evaluated with purified enzymes from a given source, and cross-synergistic interactions were studied among enzymes from different sources. Only a few pairs of enzymes showed significant synergism, and both exo-exo and endo-exo types of synergism occurred.
Components enzymes which showed the greatest synergism were further studied to determine their effectiveness for enhancing hydrolysis of Avicel by crude T. viride and P. funiculosum cellulases. Addition of $\beta$-glucosidase to either of the crude cellulases provided the greatest enhancement. In addition, exoglucanase from T. viride (Texo-2) was found to enhance P. funiculosum cellulase significantly.
Mixtures of crude T. viride and P. funiculosum cellulases also were evaluated for enhancing Avicel hydrolysis. A 1:3 ratio of T. viride to P. funiculosum cellulase was found to be the most effective. Addition of crude A. niger cellulase to either of the other crude cellulases or mixtures of the two also gave significant enhancement of hydrolysis. The highest conversion was achieved when A. niger cellulase was added to a 3:1 ratio of T. viride to P. funiculosum cellulase.
