Cellobiose metabolism

Palmer, R.E. Anderson, R.L. Cellobiose metabolism in Aerobacter aero-genes. II. Phosphorylation of cellobiose with adenosine 5-triphosphate by a-glucoside kinase. J. Biol. Chem., 247, 3415-3419 (1972)... 

The induction of this operon responds to the intracellular concentration of cAMP, which is determined by the carbon source available to the cell. When cells are grown on cellobiose or cellulose that do not inhibit adenylate cyclase, cAMP is made in sufficient quantities for induction of cellulase. On the contrary, when cells are grown on glucose or other readily metabolized carbohydrates that do inhibit adenylate cyclase. 

Physical or chemical modification of a substrate may additionally selectively affect transformation or uptake Keil and Kirchman (1992) compared the degradation of Rubisco uniformly labeled with 3H amino acids produced via in vitro translation to Rubisco that was reductively methylated with 3H-methane. Although both Rubisco preparations were hydrolyzed to lower molecular weights at approximately the same rate, little of the methylated protein was assimilated or respired. The presence of one substrate may also inhibit uptake of another, as has been demonstrated for anaerobic rumen bacteria. Transport and metabolism of the monosaccharides xylose and arabinose were strongly reduced in Ruminococcus albus in the presence of cellobiose (a disaccharide of glucose), likely because of repression of pentose utilization in the presence of the disaccharide. Glucose, in contrast, competitively inhibited xylose transport and showed noncompetitive inhibition of arabinose transport, likely because of inactivation of arabinose permease (Thurston et al., 1994). 

This enzyme, found in some bacteria which can metabolize cellulose, is theorized to be involved in the utilization of extracellular cellobiose produced by the action of cellulase (Kitaoka and Hayashi, 2002). This enzyme phosphoro-lyzes cellobiose but not cellotriose or anything larger. Cellooligosaccharides larger than cellotriose were phosphorolyzed by another phosphorylase called cellodextrin phosphorylase (EC 2.4.1.49). 

M. Mandels We are very interested in your results. In our experiments with Trichoderma viride we have had low yields of cellulase in 0.5-1.0% cellobiose culture, similar to your results with P. fluorescens. However, we could get excellent production of cellulase in these cultures when cellobiose consumption was slowed by sub-optimal temperatures, reduced aeration, or certain imbalances in the nutrients. We believe that high cellobiose levels repress cellulase formation. When the metabolic rate was decreased, however, the repression was relieved and cellobiose acted as an inducer. We believe, in fact, that cellobiose, the product of cellulase action, is the true inducer in a cellulose culture. Here the cellobiose is consumed by the fungus as rapidly as it is produced and never builds up to repressing levels. 

The role of cellobiose is complex (Figure 3). It is an inducer of cellulase, and can act also as an inhibitor of cellulase action (27). In addition, high concentrations (0.5-1.0%) of cellobiose or other rapidly metabolized carbon sources such as glucose or glycerol strongly repress cellulase formation (23, 24), so that cellulase does not normally appear... 

These effects are related to rapid metabolism of the sugar and can be prevented if the sugar is metabolized slowly. Trichoderma viride will produce as much cellulase on cellobiose as it does on cellulose if its metabolism is slowed by (1) suboptimum temperature and aeration, (2) deficiencies of mineral nutrients such as calcium, magnesium, or trace metals, or (3) excess of a mineral such as cobalt (23). 

Cellobiose must be cleaved into its constituent monosaccharides in order to be metabolized by . coli. There are two main ways in which this reaction can occur, hydrolysis and phosphorolysis. P-Glucosidase and cellobiose phosphorylase from Saccharophagus degradans were expressed in E. coli. The results showed that phosphorolysis cells tolerate common inhibitors (sodium acetate) more effectively and produce recombinant proteins more effectively than hydrolysis cells. However, hydrolysis cells utilize xylose more effectively in combination with cellobiose [192]. 

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