Cellulose glucose production

Chakrabarti, A.C. and Storey, K., Enhanced glucose production from cellulose using coimmobilized cellulase and beta-glucosidase, Appl. Biochem. Biotechnol., (1989) 22, 3, 263-78. 

The same researchers studied glucose production using beta-glucosidase immobilized with the same hydrophilic foam (Hypol 2002). " The immobilized enzyme showed 95% retention of activity after 1000 hours of continuous use at 23°C. Co-immobilization with cellulase yielded a cellulose-hydrolyzing complex with a... 

However, an enzyme that uses GDP-D-glucose as a substrate in order to synthesize a cellulose-like product has been reported to be present in developing cotton fibers during the period when primary-wall cellulose synthesis normally occurs, but is absent from older fibers undergoing active deposition of secondary-wall cellulose.303... 

In these expressions, Cx = concentration of cellulose, Ci = concentration of glucose, C0 — concentration of decomposed glucose products, kx and k2 are the rate constants for the respective reactions, Yx and Y2 are the stoichiometric coefficients, and A is the acid concentration. 

The glucose production from amorphous cellulose (by glucocellu-lase) and the cellobiose production from crystalline cellulose (by cello-biohydrolase, Ci) can be determined to assay the exo-/M,4-glucanase. 

Fig. 1. Absorbance response of equimolar amounts of soluble cellulose saccharification products glucose (G), cellobiose (G2), and cellotriose (G3) by (A) DNS assay and (B) BCA assay.

Fig. 3. Glucose production per liter of reactants over time for semibatch saccharification experiments at 15% (w/w) initial insoluble solids concentration and initial enzyme loading of 20 FPU/g of cellulose. Vacuum filtration was applied at two different times to remove glucose (vertical dashed lines). Fresh pretreated corn stover was added to replenish the volume removed by filtration. Additional enzyme was loaded at 5 FPU/g of fresh cellulose. The predicted curve was calculated by summing the amount of glucose generated by additional control experiments at 20 and 5 FPU/g of cellulose. Error bars represent averages 1 SD for two repeated experiments.

Fig. 4. Glucose production per liter of reactants over time for similar semibatch experiment as shown in Fig. 2, but at a lower enzyme loading of 10 FPU/g of cellulose (definitions of symbols and vertical dashed lines are the same). Error bars represent averages 1 SD for two repeated experiments.

Fig. 6. Cellulose conversion over time for the same experiments as shown in Fig. 5. The data represent cellulose conversions based on glucose production alone. Cellobiose measurements taken at the end of the experiments account for an additional conversion of about 4%. Error bars represent averages 1 SD for three repeated experiments.

The use of cellulases to saccharify waste cellulose has been studied for the past few years by M. Mandels and her colleagues at the U.S. Army Natick Laboratories (65). Rates of glucose production achieved are 2-4 grams/liter/hour, which is half the rate reported in commercial starch hydrolysis (4-8 grams/liter/hour). However starch is not a waste... 

Wood hydrolysis has been limited to cellulose degradation by cellulase enzymes. These en mes are typically low activity and highly inhibited by the glucose product. As mentioned above, mild acid pretreatment has been found to be an important first step in the biomass utilization process. The pretreatment is used both to break down the hemicellulose to sugars and to disrupt the lignocellulosic structure and tlie crystallinity of the cellulose. 

Besides the water elimination from the position 2,3 of the glucose unit as indicated above, other elimination positions such as 1,2 or 3,4 or 3,6 are possible. Because the side group elimination does not affect the DP value of the polymer, this reaction must be followed by the cleavage of the polymeric bonds to generate smaller molecules. These small molecules are the ones identified in cellulose pyrolysis products by techniques such as Py-GC/MS. 

Figure 4 Comparative analysis of glucose and gluconic acid production from cellulose demonstrating inhibition of cellulolytic enzymes by cellulose hydrolysis products...

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