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At least 973 records · Page 54Linked to original sources
PubMed2003

Effects of temperature and moisture on dilute-acid steam explosion pretreatment of corn stover and cellulase enzyme digestibility.

Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility of the remaining cellulose for fermentation into ethanol. In this study, dilute H2SO4 pretreatment of corn stover was performed in a steam explosion reactor at 160 degrees C, 180 degrees C, and 190 degrees C, approx 1 wt % H2SO4, and 70-s to 840-s residence times. The combined severity (Log10 [Ro] - pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180 degrees C. However, yields >90% of theoretical were found with dilute-acid pretreatments at 190 degrees C. A narrower range of higher combined severities was required for pretreatment to obtain high soluble xylose yields when the moisture content of the acidimpregnated feedstock was increased from 55 to 63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190 degrees C, using an enzyme loading of 15 filter paper units (FPU)/ g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160 and 180 degrees C pretreatments at similar combined severities but required a higher enzyme loading of approx 25 FPU/g of cellulose.

Animal Feed↗
PubMed2002

Effect of single active-site cleft mutation on product specificity in a thermostable bacterial cellulase.

Mutation of a single active-site cleft tyrosyl residue to a glycyl residue significantly changes the mixture of products released from phosphoric acid-swollen cellulose (PSC) by EIcd, the catalytic domain of the endoglucanase-I from Acidothermus cellulolyticus. The percentage of glucose in the product stream is almost 40% greater for the Y245G mutant (and for an additional double mutant, Y245G/Q204A) than for the wild type enzyme. Comparisons of results for digestion PSC and of pretreated yellow poplar suggest that the observed shifts in product specificity are connected to the hydrolysis of a more easily digestible fraction of both substrates. A model is presented that relates the changes in product specificity to a mutation-driven shift in indexing of the polymeric substrate along the extended binding-site cleft.

Actinomycetales↗
PubMed2002

Cellulase adsorption and an evaluation of enzyme recycle during hydrolysis of steam-exploded softwood residues.

The sugar yield and enzyme adsorption profile obtained during the hydrolysis of SO2-catalyzed steam-exploded Douglas-fir and posttreated steam-exploded Douglas-fir substrates were determined. After hot alkali peroxide posttreatment, the rates and yield of hydrolysis attained from the posttreated Douglas-fir were significantly higher, even at lower enzyme loadings, than those obtained with the corresponding steam-exploded Douglas-fir. The enzymatic adsorption profiles observed during hydrolysis of the two substrates were significantly different. Ultrafiltration was employed to recover enzyme in solution (supernatant) and reused in subsequent hydrolysis reactions with added, fresh substrate. These recycle findings suggested that the enzyme remained relatively active for three rounds of recycle. It is likely that enzyme recovery and reuse during the hydrolysis of posttreated softwood substrates could lead to reductions in the need for the addition of fresh enzyme during softwood-based bioconversion processes.

Adsorption↗
PubMed1997

Cellulose digestion in the wood-eating higher termite, Nasutitermes takasagoensis (Shiraki): distribution of cellulases and properties of endo-beta-1,4-glucanase.

beta-Glucosidase [EC 3.2.1.21] and endo-beta-1,4-glucanase [EC 3.2.1.4] activities were measured in the wood-eating higher termite Nasutitermes takasagoensis. beta-Glucosidase activity was present mainly in the salivary glands (66.7%) and midgut (22.2%), whereas endo-beta-1,4-glucanase activity was detected mainly in the midgut (90.1%). Specific activity of endo-beta-1,4-glucanase was also the highest in the midgut, indicating that cellulose is digested in the midgut. The major endo-beta-1,4-glucanase component of N. takasagoensis was purified from whole termites by gel filtration on Sephaoryl S-200 HR, Superdex-75 and hydroxyapatite column chromatography. Subsequently, the endo-beta-1,4-glucanase activity from a crude midgut extract was eluted in an identical volume (Kd = 0.68) to that from whole termites, suggesting the purified endo-beta-1,4-glucanase is identical to that in the midgut. The molecular weight of the purified endo-beta-1,4-glucanase was 47 kDa, and its specific activity was 1,200 units/mg. The optimal pH and temperature were 5.8 and 65 degrees C, respectively. The Km and Vmax values on carboxymethyl cellulose were 8.7 mg/ml and 2,222 units/mg, respectively. The purified endo-beta-1,4-glucanase hydrolyzed cellopentaose to cellotriose and cellobiose, and cellotetraose to cellobiose and a trace of cellotriose and glucose, but cellotriose and cellobiose were not hydrolyzed. The activity and stability on pH and temperature of the purified endo-beta-glucanase are prominent among those from various organisms.

Animals↗
PubMed2005

Purification and characterization of a thermostable-cellulase free xylanase from Syncephalastrum racemosum Cohn.

Syncephalastrum racemosum Cohn. produces an extracellular xylanase that was shown to potentially bleach pulp at pH 10 and 50 degrees C. The enzyme was found to be a dimer with an apparent molecular weight of 29 kDa as determined by SDS-PAGE. The optimum activity was found at two pH values 8.5 and 10.5; however the activity sharply decreased below pH 6 and above pH 10.5. The enzyme was stable for 72 h at pH 10.5 and at 50 degrees C. Kinetic experiments at 50 degrees C gave V(max) and K(m) of 1,400 U/ml min(-1) mg(-1) protein and 0.05 mg/ml respectively. The enzyme had no apparent requirement for cofactors, and its activity was strongly inhibited by group II b metal ions like Zn2+, Hg2+, etc. Xylan completely protected the enzyme from being inactivated by N-bromosuccinimide.

Cellulase↗
PubMed1991

Microbial beta-glucanases different from cellulases.

The beta-glucans different from cellulose are the most abundant class of polysaccharides. They are found in microorganisms and higher plants as structural entities of cell wall, as cytoplasmic and vacuolar reserve materials, and as extracellular substances. Enzyme systems capable to hydrolyze beta-glucans are produced by different microorganisms. The occurrence and nature of beta-glucanases and their substrates are reviewed. The regulation of biosynthesis of these enzymes, their properties, substrate and product specificities, mode of action and molecular cloning are described. The participation of beta-glucanases in the morphogenetic events of yeast cell is presented. The role and synergism of different types of 1,3-beta-glucanases in microbial cell wall lysis and the potential application for isolation of intracellular materials like proteins, carbohydrates, enzymes and as an analytical tool are discussed in the light of current knowledge.

Bacteria↗
PubMed1975

Fungal cellulase and hemicellulase prediction of forage digestibility.

An enzymatic procedure using Trichoderma viride carbohydrases, a fungal hemicellulase, and pepsin was developed to provide a laboratory method for predicting forage digestibility. The amount of forage dry matter solubilized by enzymes and incubation buffer was less than that in vivo or by in vitro fermentation by rumen microorganisms. Total forage dry matter solubilized by the enzymatic procedure was correlated (.92) with in vitro digestibility. Simple correlation coefficients between in vivo true digestibility of 18 forages and total dry matter solubilized by enzymes and buffer was .87; that soluble in the buffer only, .65; and that solubilized by the enzymes, .82. Correlation coefficients with in vivo true digestible amount of cell-wall and protein were greater when the forage species were considered separately than when pooled together. With this restriction, the enzymatic procedure can be a useful method for predicting forage digestibility. Fermentations with rumen inoculum however, provided more accurate predictions of in vivo digestibility in a variety of forage species.

Animal Feed↗
PubMed1981

The viscosity interaction of barley beta-glucan with Trichoderma viride cellulase in the chick intestine.

A culture filtrate from Trichoderma viride was used as a source of cellulose degrading enzymes. This filtrate, when added to a barley ration fed to chicks, improved growth and feed efficiency by 19% and 8%, respectively. The response was saturable since increasing amounts of filtrate above 50 mg/kg produced no further improvement. Barley eta-glucan was added to a corn-based diet (10 g/kg) to evaluate the effect of the culture filtrate on the viscosity of beta-glucan in the chick intestinal contents. Barley beta-glucan increased the viscosity of the supernatant of the chick intestinal contents threefold and the culture filtrate reduced the viscosity to near control levels when combined with the diet containing beta-glucan. The presence of beta-glucan in barley probably limits growth of chicks by increasing viscosity of intestinal contents.

Animals↗