Cellotriose, synthesis

S. Vonhoff, K. Piens, M. Pipelier, C. Braet, M. Claeyssens, and A. Vasella, Inhibition of cellobiohy-drolases from Trichoderma reesei. Synthesis and evaluation of some glucose-, cellobiose-, and cellotriose-derived hydroximolactams and imidazoles, Helv. Chim. Acta, 82 (1999) 963-980. 

Pseudomonas fluorescens produced two extracellular (A and B) and one cell-bound (C) cellulase components, the latter being released by treatment with EDTA-lysozyme in isotonic sucrose. Culture with 0.5% glucose formed little cellulase. Cellobiose stimulated only the synthesis of C. The formation of A and B was strikingly enhanced in cultures with cellulose, sophorose, or continuous low concentration of cellobiose. The absence of extracellular cellulase synthesis in 0.5% cellobiose culture may be caused by catabolite repression. The three cellulases were purified and characterized. None of them split cellobiose, but all hydrolyzed various cellodextrins and celluloses. C easily attacked cellotriose and cellotriosyl sorbitol, but A and B had no effect. When pure B was incubated with broken spheroplasts of sophorose-grown cells, a cellulase component indistinguishable from A was formed. 

Ps. fluorescens var. cellulosa synthesized a large amount of cellulase in 0.5% cellulose or sophorose medium, and more than 90% of the enzyme formed was released in surrounding medium (exo-type synthesis). In contrast, smaller amounts of cellulase were formed upon cultures on 0.5% cello-oligosaccharides, and more than 90% of the enzyme remained within the cells (endo-type synthesis). Since the major soluble end-products of cellulolysis by Pseudomonas cellulases in vitro were cellobiose and cellotriose (28), the direct C-source utilized by the bacterium should be these sugars even if either cellulose or cello-oligosaccharides were used as C-source. The only difference between these cultures, therefore, may be in the concentration of the end-products in each medium. 

The synthesis of extracellular cellulase activity by three strains of Clostridium thermocellum growing on cellulose has been shown to be directly related to the degradation of cellulose and to the growth of the bacteria. Cellulase was not detected when the cells grow on cellobiose. The activities of the exo-D-glucanase (pH optimum 5.2, temperature optimum 65 °C) and e do-D-glucanase (pH optimum 5.4, temperature optimum 64 °C) were compared. o-Glucose and cellobiose were released when the crude cellulase acted on cellulose, cellotetraose, and cellotriose in vitro. 

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