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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.81, #2)
Adsorption and activity of Trichoderma reesei cellobiohydrolase I, endoglucanase II, and the corresponding core proteins on steam pretreated willow by Pia Kotiranta; Johan Karlsson; Matti Siika-aho; József Medve; Liisa Viikari; Folke Tjerneld; Maija Tenkanen (pp. 81-90).
The adsorption and the hydrolytic action of purified cellulases of Trichoderma reesei, namely, cellobiohydrolase I (CBH I), endoglucanase II (EG II), and their core proteins, on steam-pretreated willow were compared. The two enzymes differed clearly in their adsorption and hydrolytic behavior. CBH I required the cellulose-binding domain (CBD) for efficient adsorption and hydrolysis, whereas EG II was able to adsorb to steam pretreated willow without its CBD. Absence of the CBD decreased the hydrolysis of cellulose by EG II, but the decrease was less pronounced than with CBH I. A linear relationship was observed between the amount of enzyme adsorbed and the degree of hydrolysis of cellulose only for CBHI. EG II and EG II core appeared to be able to hydrolyze only 1 to 2% of the substrate regardless of the amount of protein adsorbed.
Keywords: Adsorption; cellulose hydrolysis; cellobiohydrolase; endoglucanase; Trichoderma reesei
Comparison of various optimization approaches for fed-batch ethanol production by Jung-Heon Lee (pp. 91-106).
Various optimization techniques have been proposed to optimize the feedrate profile to maximize ethanol production. Among them are the differential algebraic system (DAS) approach, Kelly transformation approach, singular control approach, and on-off control approach. These methods are compared and it is shown that the DAS approach and Kelly transformation method are equivalent. A nonsingular transformation approach is presented. The performance obtained with the nonsingular approach is the same as that obtained with the singular approach and better than those obtained with the DAS and on-off control approaches.
Keywords: Optimization; differential algebraic system; nonsingular transformation
Anaerobic toxicity and biodegradability of hydrolysis products of chemical warfare agents by Vladimir I. Sklyar; Tatyana P. Mosolova; Irina A. Kucherenko; Natalya N. Degtyarova; Sergey D. Varfolomeyev; Sergey V. Kalyuzhnyi (pp. 107-117).
The toxicity and biodegradability of the main hydrolysis products of chemical warfare agents were investigated under methanogenic conditions. Among the tested substances, only MPhA does not have any toxic effect with regard to the aceticlastic methanogenic activity. The toxicity of other compounds varied between moderate (TDG, mercaptoethanol) to strong (ethanolamine, diisobutyl ester of MPhA). Biodegradability tests showed that all the products of chemical detoxification of mustard gas (ethanolamine, ethylene glycol, TDG, mercaptoethanol) can be biomineralized under methanogenic conditions. On the contrary, phosphorus-containing compounds from the chemical detoxification of nerve warfare agents (Sarin, Soman, Vx-gases) are quite persistent under these conditions.
Keywords: Anaerobic biodegradation; chemical warfare; ethanolamine; mercaptoethanol; methylphosphonic acid; thiodiglycol; toxicity
Xylitol production from wood hydrolyzates by entrapped Debaryomyces hansenii and Candida guilliermondii cells by Jose Manuel Domínguez; Jose Manuel Cruz; Enrique Roca; Herminia Domínguez; Juan Carlos Parajó (pp. 119-130).
Debaryomyces hansenii cells were entrapped in Ca-alginate beads and used for producing xylitol from wood hydrolyzates. Batch experiments showed that bioconversion was severely hindered when Ca-alginate beads were hardened with Al3+ solutions. As an alternative to Al3+ hardening, the improvements in both mechanical stability of bioparticles and fermenting ability of the immobilized system derived from using increased concentrations of sodium alginate were assessed. The best results were obtained using a 4% (w/v) Na-alginate solution in the gelification step. This concentration was selected to perform continuous fermentations in a packed-bed reactor using raw or charcoal-treated hydrolyzates (15.5 g of xylose/L) with two different yeasts: Candida guilliermondii and Debaryomyces hansenii. With a final cell concentration of about 50 g of cells/L (0.075 g of cells/g of beads), the volumetric productivities reached with these yeasts in media made from charcoal-treated hydrolyzates were 0.58 and 0.91 g/L·h, respectively.
Keywords: Ca-alginate; Candida guilliermondii ; Debaryomyces hansenii ; hemicellulose hydrolyzate; xylitol
A kinetic study on lipase-catalyzed interesterification of soybean oil with oleic acid in a continuous packed-bed reactor by Masamichi Akimoto; Yoshiko Nagashima; Daiki Sato (pp. 131-142).
To provide a mathematical basis for the design and operation of a continuous, packed-bed reactor for the interesterification of soybean oil, soybean oil that contains 22.7% oleoyl and 54.3% linoleoyl moieties as molar acyl moiety composition was interesterified in hexane with oleic acid, using an immobilized sn-1,3-specific lipase (Lipozyme IM) from Mucor miehei. The reaction was carried out in a U-shaped Pyrex glass-made packed-bed reactor at 37°C in the following system: concentration of soybean oil in the feed stream=12.5 wt%, molar ratio of fatty acid to soybean oil=3.0, and water content in the feed stream=1340–2340 ppm. At these water contents, Lipozyme IM gave practically the same catalytic activity, and the content of triacylglycerols in the product oil was 91–94 wt%. Rate equations for the change in oleoyl and linoleoyl moiety compositions in soybean oil were derived and their validity was confirmed experimentally. On the other hand, the catalytic activity of Lipozyme IM decayed in the first-order fashion. Based on these deactivation kinetics, the flow rate of the feed stream is simulated for the operation of a continuous, packed-bed reactor at 37°C that produces an oil of a fixed composition of oleoyl moiety.
Keywords: Interesterification; acidolysis; soybean oil; oleic acid; linoleic acid; lipase; Lipozyme IM; packed-bed reactor; kinetics; deactivation