Abstract1) Growth of Cephalosporium acremonium was supported by a variety of carbon sources ranging in complexity from glucose to native cotton. Growth on carboxymethyl cellulose was however limited, believed to be due to the metabolic inability of the organism to utilize the substituted products of attack. Although viable cultures of C.acremonium were capable of rapidly solubilizing cotton boll fibres which had never been allowed to dehydrate, growth on dried cotton fibres was characterized by the inability of the organism to produce complete fibre solubilization, 2) Substrates possessing B-1, 4-glycosidic bonds produced enhanced titres of cellulolytic enzymes but were not essential for enzyme induction, 3) Cell-free extracts obtained from such cultures possessed appreciable hydrolytic activity towards cellobiose, CMC and acid swollen cellulose, but were considerably less active on native cotton fibres, 4) Although the presence of cell-bound cellulase enzymes was established, further investigation indicated these components to be similar in type, number and mode of action to those isolated from culture filtrates, 5) Fractionation of cell-free extracts resolved the cellulase system into three distinct enzymic components whose actions overlapped, and which differed mainly in molecular weight and in their relative affinity for substrates of varying complexity. These consisted of (a) a B-glucosidase possessing a molecular weight in excess of 200,000 and active mainly on soluble low DP substrates; (b) a CMC-ase with a molecular weight of approximately 45,000, active on CMC and the higher DP oligosaccharides. Although this component exhibited no hydrolytic activity towards insoluble cellulosic substrates, the enzyme was found to possess slight S-factor activity and to be capable of producing a detectable decrease in the tensile strength of cotton, (c) Cx-cellulase, an enzyme with a molecular weight of about 11,200 which exhibited little substrate specificity. This enzyme was responsible for the activity of the organism towards native cotton, but was also capable of producing extensive hydrolysis and depolymerization of less structurally complex substrates and oligosaccharides. 6) All three components were found to be complexed with carbohydrate. 7) Viscometric studies indicated the action of the depolymer- izing CMC-ase and Cx-cellulase components to be endoenzymic. 8) Enzyme/substrate affinity determinations revealed a decrease in affinity as the structural complexity of the substrate increased. These results suggested the existence of only a limited number of sites in native cotton fibres accessible or susceptible to attack by the Cx-cellulase. 9) Evidence of increased crystallinity in the residual short fibres produced from native cotton by cultures of C.acremonium suggested that such sites consisted of essentially amorphous cellulose. Evidence in support of this theory was provided by the observation that amorphous undried cotton boll fibres were completely solubilized by this organism. 10) The extensive but incomplete degradation of native cotton by viable cultures of C.acremonium was acheived without the aid of a C1 component. Solubilization of the residual short fibres could be rapidly completed by a culture of T.viride.
|Date of Award||1973|
The cellulase system of Cephalosporium acremonium Corda.
Wright, D. (Author). 1973
Student thesis: Doctoral Thesis › PhD