Cellobiose Subject

In addition to catabolite repression, the cellulase enzymes themselves are subject to end-product inhibition. For example, as glucose accumulates during saccharification, it interacts noncompetively with cellobiase to inhibit further activity of this enzyme (6). Similar inhibition of endoglucanases occurs when cellobiose accumulates in a saccharification reactor (18,19,20). 

In regard to the cell-bound cellulase, however, no exact locality and function in the cell has been fully studied in general. The cells of Ps. fluorescens grown on 0.5% cellobiose were, therefore, fractionated principally according to the method of Burrous and Wood (5). At the same time, part of the same sample of cells was subjected to direct disintegration by sonic treatment and the sonicate was centrifuged to use as a standard for enzyme assays. The results are summarized in Table I. 

The methods of methylation were first launched by the preparation of crystalline tetramethyl-glucose (7). Galactose (8), sucrose, and maltose (9) were subjected to methylation, and in 1906 the method was extended to determine die stmcture of the natural glucoside, salicin (10). Denham and Woodhouse (11) in 1910 were able to introduce methyl groups into cellulose. A modification of die mediylation method enabled it to be apphed to the preparation of glucosides and mediylated glucosides (12) and the simplification of work in such cases facilitated the eonstitutional study of sucrose, lactose, maltose, and cellobiose (13, 14, 15). 

Perhaps the material can be reacted or degraded to form a soluble compound, which can then be characterized. An example is cellulose, a natural polymer that was part of the earliest discussions. Insoluble itselt it can be acetylated to form soluble cellulose acetate for molecular weight determination, by osmometry at the time. Then it was subjected to degradation to glucose and cellobiose, which were determined to be the monomer and dimer, respectively. 

Cellulose is a carbohydrate, the structure of which may be deduced as follows. The molecular formula of cellulose is (C6HioOs)n, where n is a few thousand (see later). Hydrolysis of cellulose by boiling with concentrated hydrochloric acid yields D-glucose (II) in 95-96% yield. Thus cellulose is a polyanhydroglucose. When cellulose is subjected to acetolysis (i.e., simultaneous acetylation and hydrolysis) by treatment with a mixture of acetic anhydride and concentrated sulphuric acid, cellobiose octa-acetate is formed. Thus the structure of cellulose is based on the cellobiose unit. Cellobiose is known to be the disaccharide, 4-0-j3-D-glucopyranosyl-D-glucopyranose (III). Finally, very careful acetolysis of cellulose produces a cellotriose, a ceUotetraose and a cellopentaose and in each of these all the 1,4-links have been shown to be j3-links (from calculations of the... 

Endoglucanases hydrolyze 3-l,4-glycosidic linkages randomly. They do not attack cellobiose but hydrolyze cellodextrins, phosphoric-acid swollen cellulose and substituted celluloses such as carboxymethyl (CM)- and hydroxyethyl (HE)-cellulose. Trichoderma seems to secrete a number of respective enzymes into the medium, of which two (EG I, EG III) have been the subject of a more detailed investigation. It should be noted that some confusion has arisen in the past from the fact that EG III was termed EG II by several authors from the US. However, this has been overcome now. 

As shown in Table 4.29, the Ci and Cx factors, which were found to be endo- and exo-l,4-P-glucanases respectively, hydrolyze cellulose to cellobiose. Since the Ci factor is increasingly inhibited by its product, a cellobiase is needed so that cellulose breakdown is not rapidly brought to a standstill. However, cellobiase is also subject to product inhibition. Therefore, complete cellulose degradation is possible only if cellobiase is present in large excess or the glucose formed is quickly eliminated. 

The following disaccharides and derivatives have been subjected to conformational analysis by n.m.r spectroscopy and/or computational methods cellobiose in aqueous solution, methyl P-xylobioside, methyl P-cellobioside, P-gentibiose, all possible monomethyl ethers of methyl p-lactoside, unsaturated, sulfated disaccharides, such as IS, obtained by cleavage of glycosaminoglycans with lyases, ° chondroitin sulfate-related ctmqmunds, such as 16, the uronic... 

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