No description available.

No description available.

No description available.

Under cellulolytic conditions, the white-rot fungus Trametes versicolor produces cellobiose dehydrogenase (CDH), an enzyme with a number of biochemical properties that are potentially relevant to the degradation of lignin and cellulose. To clarify its biochemical properties, CDH was purified from cultures of T. versicolor. Two isoforms of CDH were found: a 97 kDa isoform with both heme and flavin cofactors, and an 81 kDa isoform with a flavin cofactor. Both isoforms of CDH were found to be quite non-specific in their reductive half reactions. The flavin enzyme catalyzed many of the same reactions as the heme/flavin enzyme, but less efficiently. The flavin isoform reduced Fe(III) and Cu(II) only at concentrations well above those found physiologically. Thus the heme/flavin enzyme, but not the flavin enzyme, could be involved in promoting and sustaining the generation of hydroxyl radicals (·OH) by Fenton's chemistry. / To characterize further the structural features of CDH, a genomic clone was isolated and sequenced. CDH was found to consist of 748 amino acids, without its predicted 19 amino acid signal peptide. Consistent with the domain structure of other CDHs, T. versicolor CDH appeared to be divided into an amino terminal heme domain and a carboxy terminal flavin domain, connected by a hydroxyamino acid-rich linker. Within the flavin domain, a putative cellulose-binding domain (CBD) was found by alignment to the hypothesized CBD of P. chrysosporium CDH. The CBD of CDH appeared to be structurally unrelated to other CBDs which have been reported. / A cDNA clone encoding T. versicolor CDH was isolated by RT-PCR. Using this clone, three vectors for the heterologous expression in Aspergillus oryzae of CDH were prepared. These vectors were built by performing in-frame fusions of the cDNA to control sequences from the highly expressed A. oryzae amylase gene. These vectors were transformed into A. oryzae and one strain was isolated which contained the expression construct DNA. / A rapid method for cloning cdh-like genes was developed. Using short stretches of amino acids completely conserved within T. versicolor and P. chrysosporium CDH, PCR primers were designed to amplify a homologous gene from other fungi. The primers were tested using genomic DNA of Pycnoporus cinnabarinus. A 1.8-kb fragment of P. cinnabarinus cdh was thereby amplified and cloned, and its sequence was determined. The three CDHs displayed very high homology at the amino acid level. / Finally, to probe the role of CDH in lignocellulose degradation by T. versicolor, a "knockout" vector was constructed consisting of a phleomycin-resistance cassette inserted into the protein coding sequence of cloned T. versicolor cdh. T. versicolor was transformed with the knockout vector and the transformants were analyzed for their CDH-producing phenotype. Three isolates were found that produced no detectable CDH. Biobleaching and delignification by the CDH(-) strains appeared to be unaffected, suggesting that CDH does not play an important role in these processes.

No description available.

Hornification is the term used to describe the irreversible changes that occur in cellulose fibers due to recycling. While the effects of hornification have been documented, there are several conflicting hypotheses that attempt to explain the causes. In this research, AFM surface adhesion measurements made on virgin and recycled bleached kraft pulp show that recycling increases the apparent hydrophilicity of the fiber surface. Yet, the water retention values and tensile strength decrease as expected, which is consistent with internal cross-linking of the bonding sites and a reduction in hydrophilicity. Recycling does not affect the amount of monolayer water bound to the fiber surface indicating that the pore water is reduced but not the water bound to fiber surfaces. It is proposed that the contact area between the AFM tip and the fiber is greater for recycled material than for virgin. Image analysis of the fiber surface supports this conclusion, revealing a decrease in the surface roughness. The irregularity of fiber surfaces is apparent in AFM images at all but the smallest scales, with macroscopic fiber features dominating the roughness analyses of images larger than 2500 square nanometers. Hence, in this instance, the surface adhesion values are more a measure of the topography of the surface than of its chemistry. An application to newsprint is illustrated, revealing the limitations of AFM analysis of samples with a high degree of variability.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 86-89).

Thesis (M.S.)--Virginia Polytechnic Institute, 1961. / Vita. Abstract. Includes bibliographical references (leaves 83-89). Also available via the Internet.

Thesis (M.Sc. Biological Sciences)--University of Waikato, 2008. / Title from PDF cover (viewed February 25, 2009) Includes bibliographical references (p. 70-78)

Thesis (M.App.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 146-152). Also available in electronic format on the Internet.