Many laboratories have developed processes by which liquid fuels and chemicals may be produced from our most plentiful renewable resource, cellulose. Because cellulose hydrolysis is the rate-limiting step in the production of glucose, ethanol, or other final products, pretreatment of cellulosics to increase both the rate and extent of enzymatic hydrolysis has been an area of intense interest. Although purified cellulosics have been the subjects of much research, experimentation has shifted to more commercially practical lignocellulosics. What remains relatively unknown are the effects of various physical and chemical modifications achieved during pretreatment with respect to enzymatic hydrolysis and subsequent ethanol production from these lignocellulosics.This study was initiated to determine the relationships between the intrinsic physical and chemical factors of substrate composition, cellulose crystallinity, and particle size and the extent of enzymatic hydrolysis of the major municipal-solid-waste (MSW) components, newspaper and cormgated cardboard. Through these evaluations, the modifications of MSW that result in increased conversions to ethanol have been determined.
MATERIALS AND METHODSTrichoderma reesei QM 94 14G, obtained originally from the American Type Culture Collection (Rockville, MD) was used to produce a full-complement cellulase system consisting of endoglucanase , cellobiohydrolase, and cellobiase activities' to hydrolyze cellulose in both saccharification and SSF. Permanent stock cultures were maintained as lyophylized spores, and working stock cultures were allowed to sporulate on Difco potato dextrose agar (Difco, Detroit, MI) and then were maintained at 4°C.
Both NAD- and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (G3PDH) (EC 1.2.1.12) activities were detected in glucose-grown cells of Pseudomonas aeruginosa strain PAO. After growth on gluconeogenic substrates such as citrate, the activity of the NAD-G3PDH was reduced severalfold in contrast to little change for the NADP-G3PDH. The two G3PDH activities could be separated by ammonium sulphate fractionation. PAGE revealed the presence of two G3PDH isoenzymes of 140 (NADP-specific) and 315 (NAD-specific) kDa. Slight differences were observed in the thermostabilities and pH optima of the two enzymes whereas the regulation of their activities by various compounds varied strongly. The NADP-G3PDH enzyme was activated by ATP, reduced NAD, and fructose 6-phosphate. It was inhibited by fructose 1,6-diphosphate and 6-phosphogluconate. The NAD-G3PDH enzyme was inhibited by ATP, reduced NAD, and 6-phosphogluconate; it was slightly activated by reduced NADP. The possible roles of these isoenzymes in the control of hexose catabolism and gluconeogenesis in P. aeruginosa are discussed.
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