Format:
150 S.
Edition:
Mikrofilm-Ausg. Ann Arbor, Mich. Univ. Microfilms Internat. 1982 1 Mikrofilm : 35 mm [Mikrofilm-Ausg.]
Content:
The visual patterns of the process of enzymatic cellulose degradation were established at the macromolecular level utilizing high resolution negative staining electron microscopic techniques. The employment of ultrathin carbon films as a support matrix for negative staining allowed observations of the fine structure of cellulosic ribbons produced by the Gram-negative bacterium Acetobacter xylinum. Visualization of cellulose microfibrils and bundles of microfibrils of various sizes suggests that A. xylinum cellulose ribbons are comprised of a heirarchical arrangement of crystalline cellulose structures. Individual enzyme molecules from the cellulase enzyme system of the imperfect fungus Trichoderma reesei QM9414 were imaged, as well as the binding of the enzymes to the surface of the cellulose substrate, and the subsequent fine structural changes which occur in cellulose structure during enzymatic degradation. After short exposures to cellulase enzyme solutions, ribbon surfaces were obscured by bound particles with diameters ranging from 3 to 7 nm with a mean diameter of 5.4 (+OR-) 0.2 nm. Negative staining of dilute cellulase enzyme solutions revealed spherical particles with diameters ranging from 3 to 7 nm with a mean diameter of 5.4 (+OR-) 0.1 nm. Evidence was presented that the particles observed in the solution and bound to the cellulose surfaces are, in fact, cellulase enzymes. Visual patterns of the process of cellulose degradation were established. Enzymes were initially observed bound to the cellulose ribbon. Within 10 min, the ribbon was split along its long axis into bundles of microfibrils which were subsequently thinned until they were completely dissolved within 30 min. The actions of purified components of the enzyme system were examined and compared with the synergistic action of the complete system. Incubations with purified components of the cellulase enzyme system produced less dramatic changes in ribbon structure. Purified 1,4-(beta)-D-glucan cellobiohydrolase I(D) (EC 3.2.1.91) produced no visible change in cellulose structure. Purified endo-1,4-(beta)-D-glucanase IV (EC 3.2.1.4) produced some splaying of ribbons into microfibril bundles. When purified enzymes were present simultaneously in an incubation admixture, cellulose was completely degraded in the normal manner within 30 min. Sequential incubation in purified Endoglucanase IV and Cellobiohydrolase I(D) illustrated the necessity of simultaneous presence of these two enzymes before synergistic degradation of cellulose is possible. The observed actions of the cellulose enzyme system, purified components of the system applied singly or sequentially, or admixtures of the purified components, were consistent with the existing biochemical data on the mode of action of the cellulase enzyme system.
Note:
Chapel Hill, NC, Univ. of North Carolina, Diss., 1981
,
Mikrofilm-Ausg.:
Language:
English
URL:
Katalogkarte der UB Frankfurt
