Date of Award

12-2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Advisor

Barbara J.W. Cole

Second Committee Member

Raymond C. Fort, Jr.

Third Committee Member

Bruce L. Jensen

Abstract

Over the last few years, increased attention in the pulp and paper industry has focused on saving energy, which results in lower production costs, and minimizing pollution. Environmental groups urge the replacement of chlorine agents in the bleaching of pulp. This is due to the production of dioxins, which are toxic. Biopulping, which is the use of fungal enzymes in the pulping process, has been an alternative investigated over the last 30 years. This process is environmentally friendly. However, more research is needed to completely understand the mechanism of the biopulping process for it to successfully replace the existing pulping and bleaching processes. Two of the more studied fungi in the biopulping process are the white rot and brown rot fungi. The white rot fungus has been shown to degrade both cellulose and lignin, whereas the brown rot breaks down only cellulose and modifies lignin, which can then undergo further degradation. Research done on one type of fungus will ultimately aid in understanding the other and also contribute to the overall understanding of biopulping. An extensively studied brown rot fungus is Gloeophyllum trabeum, which utilizes a hydroquinone-driven Fenton system (Fe2+ + H2O2) to generate hydroxyl radicals. The hydroxyl radicals are powerful oxidants that can degrade cellulose and modify lignin. This fungus also utilizes an enzyme (quinone oxidoreductase) that recycles hydroquinones, which are needed to generate hydroxyl radicals. The enzyme uses flavin adenine dinucleotide (FAD) to transfer electrons for the reduction of quinones to hydroquinones. Our research focused on mimicking the hydroquinone-driven Fenton reaction in the brown rot fungus and observing its effect on three carbohydrate model compounds (methyl-β-D-glucoside, methyl-β-D-cellobioside, and methyl-β-D-galactoside). In addition, computer modeling was used to generate a protein model structure for the quinone oxidoreductase as well as docking flavin adenine dinucleotide into this structure. The results show that degradation of the three model compounds occurs when they are exposed to the hydroquinone-driven Fenton system. Some of the products are similar to the ones observed by Guay et al (1999) in which carbohydrate model compounds were exposed to a UV/H2O2 system, which generated hydroxyl radicals. The proposed mechanisms suggest attack by hydroxyl radicals on the carbohydrate model compounds occur at the anomeric position. With the computer modeling, two different methods were used to obtain structures for quinone oxidoreductase. A comparison of the two structures, using Swiss PDB viewer, showed the root mean square deviation (rmsd) was 0.95 Angstroms, which indicates a favorable comparison for the two structures. The docking of FAD into one of the model structures was also successful.

Download

Share