戊糖和己糖共发酵生产燃料乙醇条件研究

利用嗜鞣管囊酵母P-01对木糖和葡萄糖共发酵生产燃料乙醇的条件进行了试验研究,结果表明,木糖和葡萄糖混合液生产燃料乙醇的最佳条件为发酵液的pH值5.5、30℃、摇床转速120 r/min、接种量10%、发酵液初始糖浓度6%、葡萄糖与木糖之比为2、发酵周期为84h。在最佳发酵条件下,发酵醪液中的燃料乙醇浓度为2.101%,糖醇转化率为35%。     

Non-oxidative synthesis of pentose 5-phosphate from hexose 6-phosphate and triose phosphate by the L-type pentose pathway

1. Ribose 5-phosphate was non-oxidatively synthesized from glucose 6-phosphate and triose phosphate by an enzyme extract prepared from rat liver (RLEP). Analysis of the intermediates by GLC, ion-exchange chromatography and specific enzymatic analysis, revealed the presence of the following intermediates of the L-type pentose pathway: altro-heptulose 1,7-bisphosphate, arabinose 5-phosphate and D-glycero D-ido octulose 8-phosphate. 2. With either [1-14C] or [2-14C]glucose 6-phosphate as diagnostic substrates, the distribution of 14C in ribose 5-phosphate was determined. At early time intervals (0.5-8 hr), [1-14C]glucose 6-phosphate introduced 14C into C-1, C-3 and C-5 of ribose 5-phosphate, at 17 hr 14C was confined to C-1. With [2-14C]glucose 6-phosphate as substrate, 14C was confined to C-2, C-3 and C-5 of ribose 5-phosphate during early times (0.5-8 hr), while at 17 hr 14C was located in C-2. 3. The transketolase exchange reaction, [14C]ribose 5-phosphate + altro-heptulose 7-phosphate in equilibrium ribose 5-phosphate + [14C]altro-heptulose 7-phosphate, was demonstrated for the first time using purified transketolase, its activity was measured and it is proposed to play a major role in the relocation of 14C into C-3 and C-5 or ribose 5-phosphate during the prediction labelling experiments. 4. The coupled transketolase-transaldolase reactions, 2 fructose 6-phosphate in equilibrium altro-heptulose 7-phosphate + xylulose 5-phosphate and 2 altro-heptulose 7-phosphate in equilibrium fructose 6-phosphate + D-glycero D-altro octulose 8-phosphate were demonstrated with purified enzymes, but are concluded to play a minor role in the non-oxidative synthesis of pentose 5-phosphate and octulose phosphate by (RLEP). 5. The formation of gem diol and dimers of erythrose 4-phosphate is proposed to account in part for the failure to detect monomeric erythrose 4-phosphate in the carbon balance studies. 6. The equilibrium value for the pentose pathway acting by the reverse mode in vitro was measured and contrasted with the value for the pathway acting in the forward direction. The initial specific rates of the pentose pathway reactions in vitro for the reverse and forward directions are measured. 7. The study which includes carbon balance, time course changes and 14C prediction labelling experiments reports a comprehensive investigation of the mechanism of the pentose pathway acting reversibly.     

The fermentation of hexose and pentose sugars by Candida shehatae and Pichia stipitis

Summary The fermentation by Candida shehatae and Pichia stipitis of xylitol and the various sugars which are liberated upon hydrolysis of lignocellulosic biomass was investigated. Both yeasts produced ethanol from d-glucose, d-mannose, d-galactose and d-xylose. Only P. stipitis fermented d-cellobiose, producing 6.5 g·l^-1 ethanol from 20 g·l^-1 cellobiose within 48 h. No ethanol was produced from l-arabinose, l-rhamnose or xylitol. Diauxie was evident during the fermentation of a sugar mixture. Following the depletion of glucose, P. stipitis fermented galactose, mannose, xylose and cellobiose simultaneously with no noticeable preceding lag period. A similar fermentation pattern was observed with C. shehatae, except that it failed to utilize cellobiose even though it grew on cellobiose when supplied as the sole sugar. P. stipitis produced considerably more ethanol from the sugar mixture than C. shehatae, primarily due to its ability to ferment cellobiose. In general P. stipitis exhibited a higher volumetric rate and yield of ethanol production. This yeast fermented glucose 30–50% more rapidly than xylose, whereas the rates of ethanol production from these two sugars by C. shehatae were similar. P. stipitis had no absolute vitamin requirement for xylose fermentation, but biotin and thiamine enhanced the rate and yield of ethanol production significantly.Nomenclature _max Maximum specific growth rate, h^-1 - Q _p Maximum volumetric rate of ethanol production, calculated from the slope of the ethanol vs. time curve, g·(l·h)^-1 - q _p Maximum specific rate of ethanol production, g·(g cells·h) - Y _p/s Ethanol yield coefficient, g ethanol·(g substrate utilized)^-1 - Y _x/s Cell yield coefficient, g biomass·(g substrate utilized)^-1 - E Efficiency of substrate utilization, g substrate consumed·(g initial substrate)^-1·100     

Recombinant Escherichia coli engineered for production of L-lactic acid from hexose and pentose sugars

Recombinant Escherichia coli have been constructed for the conversion of glucose as well as pentose sugars into L-lactic acid. The strains carry the lactate dehydrogenase gene from Streptococcus bovis on a low copy number plasmid for production of L-lactate. Three E. coli strains were transformed with the plasmid for producing L-lactic acid. Strains FBR9 and FBR11 were serially transferred 10 times in anaerobic cultures in sugar-limited medium containing glucose or xylose without selective antibiotic. An average of 96% of both FBR9 and FBR11 cells maintained pVALDH1 in anaerobic cultures. The fermentation performances of FBR9, FBR10, and FBR11 were compared in pH-controlled batch fermentations with medium containing 10% w/v glucose. Fermentation results were superior for FBR11, an E. coli B strain, compared to those observed for FBR9 or FBR10. FBR11 exhausted the glucose within 30 h, and the maximum lactic acid concentration (7.32% w/v) was 93% of the theoretical maximum. The other side-products detected were cell mass and succinic acid (0.5 g/l). Journal of Industrial Microbiology & Biotechnology (2001) 27, 259–264. Received 05 November 2000/ Accepted in revised form 03 July 2001     

Introduction and metabolism of pentose and hexose phosphates in permeabilized Morris hepatoma 5123TC cells

Metabolism of arabinose 5-P, ribose 5-P and glucose 6-P in permeabilized and resealed Morris hepatoma 5123TC cells was investigated by measuring the contribution of these compounds to nucleic acid biosynthesis. The level of [14C]-arabinose (non-phosphorylated) incorporation into nucleic acids was slight, presumably due to the low activity of the transport system or the absence or low activity of a specific 'kinase' enzyme. The permeabilizing procedure involved the brief treatment of Morris hepatoma 5123TC cells with lysolecithin and resulted in a cell population which was permeable to charged compounds i.e. sugar phosphates and nucleotides, that otherwise could not cross the plasma membrane. The permeabilized (and resealed cells) retained normal cellular morphology and intactness of specific organelles as judged by the maintenance of functional properties. Following permeabilization, these cells resealed when transferred back to normal growth medium, and continued to divide and increase at the same rates as control non-permeabilized cell cultures. The permeabilized cells incorporated deoxyribonucleotides ([methyl -3H]-TTP) into DNA at a linear rate of 0.047 nmol per 10(7) cells min-1, representing 90-100 per cent of the DNA synthesis rate in vivo. The permeabilization technique, when coupled with procedures to establish cell synchrony, permitted the comparative estimate of the contributions of [14C]-labelled arabinose 5-P, ribose 5-P and glucose 6-P to RNA, DNA, amino acids, CO2, lactate and sugar mono- and bisphosphates. The percentage of [14C]-isotope incorporated into total nucleic acids by these three labelled sugar phosphates were 2.3, 4.9 and 6.3 respectively. Possible reasons for the lower incorporation of 14C from arabinose 5-P are given. The results are consistent with the proposal that arabinose 5-P, an intermediate of the L-type pentose pathway activity of 5123TC cells, was incorporated into nucleic acids by its interconversion with ribulose 5-P and ribose 5-P and thus into PRPP. This study represents the first report of sugar phosphate as opposed to free sugar metabolism by tumour cells in culture.     

Ethanol fermentation of hexose and pentose wood sugars produced by hydrogen-fluoride solvolysis of aspen chips

Summary Hexose and pentose sugars, produced by hydrogen-fluoride solvolysis of aspen wood chips, were totally consumed in a coculture fermentation by Zymomonas mobilis and a mutant of Clostridium saccharolyticum. Z. mobilis converted the glucose to ethanol, while the mutant, which was improved in both ethanol production and tolerance, converted the xylose component to ethanol. A high conversion efficiency of wood sugars to ethanol was obtained, and the cells after the fermentation were successfully used for cell recycle.NRCC no. 23211     

A pathway for the interconversion of hexose and pentose in the parasitic amoeba Entamoeba histolytica.

The following three potent inhibitors of hepatocytic proteolysis were investigated to see if they would inhibit the intracellular inactivation of enzymes: chymostatin and leupeptin (proteinase inhibitors) and methylamine (a lysosomotropic weak base). Chymostatin inhibited the inactivation of two of the three enzymes tested: tyrosine aminotransferase (EC 2.6.1.5) and tryptophan oxygenase (tryptophan 2,3-dioxygenase, EC 1.13.11.11). Leupeptin had no effect on any of the enzymes, whereas methylamine had only a weak inhibitory effect on tyrosine aminotransferase inactivation. Apparently proteolytic cleavage (probably by a non-lysosomal proteinase, since only chymostatin is effective) is involved in the inactivation of tyrosine aminotransferase and tryptophan oxygenase. The third enzyme, benzopyrene hydroxylase (flavoprotein-linked mono-oxygenase, EC 1.14.14.1), is probably inactivated by a non-proteolytic mechanism.     

Absorption of hexose and pentose sugars in vivo in perfused intestinal segments in the fowl.

1. Rates of absorption of two hexose (D-glucose and D-galactose) and two pentose (D-xylose and D-arabinose) sugars were measured by in vivo perfusion, in jejunum, ileum and (distal) caecum, in immature hens conditioned to either a standard (ST) or "high fibre" (ST + 20% grass) diet. 2. Each bird was tested in one intestinal segment with all four (U-14C-labelled, 10 mM) sugars, with either the hexoses preceding the pentoses or vice versa. 3. With all treatments, absorption rates of the hexoses were alike, as were those of the pentoses. Hexose absorption was twice as fast as pentose absorption in jejunum and ileum with both dietary pretreatments, whereas in caecum hexose and pentose rates were similarly high, except when pentose (and its associated fluid transfer) was apparently inhibited by prior hexose absorption with the ST diet. 4. With the ST diet, hexose absorption (per unit length and dry weight) was faster in caecum than in jejunum and ileum, and pentose absorption was also fastest in caecum when all pentose data from testing after hexose were excluded. 5. With the ST/grass diet, hexose absorption was faster in jejunum than in ileum and caecum when expressed per unit length, and pentose absorption was fastest in caecum on a dry weight basis. 6. Hexose absorption was faster in jejunum and slower in caecum with the ST/grass pretreatment than with ST. However, the dietary comparison was not conclusive because it involved birds form (two) different hatches (of similar age and weight) tested at different times.     

The hexose monophosphate pentose pathway in fibroblasts deficient in L-ornithine: 2-oxoacid aminotransferase activity

Δ¹-pyrroline-5-carboxylate has been shown to exert a strong stimulatory effect on the hexose monophosphate pentose pathway of glucose oxidation in fibroblasts. In gyrate atrophy, activity of an enzyme which can form Δ¹-pyrroline-5-carboxylate is absent. The effect of this deficiency on the operation of the hexose monophosphate pentose pathway in fibroblasts from gyrate atrophy patients has not been examined. This communication describes such a study and shows that glucose metabolism through this pathway is the same for gyrate atrophy and normal fibroblasts either in the presence or absence of added Δ¹-pyrroline-5-carboxylate.     

Simultaneous consumption of pentose and hexose sugars: an optimal microbial phenotype for efficient fermentation of lignocellulosic biomass

Lignocellulosic biomass is an attractive carbon source for bio-based fuel and chemical production; however, its compositional heterogeneity hinders its commercial use. Since most microbes possess carbon catabolite repression (CCR), mixed sugars derived from the lignocellulose are consumed sequentially, reducing the efficacy of the overall process. To overcome this barrier, microbes that exhibit the simultaneous consumption of mixed sugars have been isolated and/or developed and evaluated for the lignocellulosic biomass utilization. Specific strains of Escherichia coli, Saccharomyces cerevisiae, and Zymomonas mobilis have been engineered for simultaneous glucose and xylose utilization via mutagenesis or introduction of a xylose metabolic pathway. Other microbes, such as Lactobacillus brevis, Lactobacillus buchneri, and Candida shehatae possess a relaxed CCR mechanism, showing simultaneous consumption of glucose and xylose. By exploiting CCR-negative phenotypes, various integrated processes have been developed that incorporate both enzyme hydrolysis of lignocellulosic material and mixed sugar fermentation, thereby enabling greater productivity and fermentation efficacy.     

Bioconversion of corn stover derived pentose and hexose to ethanol using cascade simultaneous saccharification and fermentation (CSSF)

A cascade type of fermentation, designated the cascade simultaneous saccharification and fermentation (CSSF), was studied to convert corn stover derived pentose and hexose to ethanol with reduced enzyme input. In detail, each step of CSSF utilizes two sequential SSF phases operating on pentose and hexose, i.e., pentose conversion using xylanase, endo-glucanase, and recombinant Escherichia coli (KO11) with minimal glucose conversion in the first phase SSF, and hexose conversion in the second phase SSF using cellulase, β-glucosidase, and Saccharomyces cerevisiae (D(5)A). In this cascade scheme, multiple stages of 1st and 2nd phase SSF were performed in series; enzymes are recycled from the fermentation broth of the last stage for the use of the next stage. This bioconversion process yielded up to 60% of the theoretical maximum ethanol yield based on the total sugars in untreated corn stover, while enzyme loadings were reduced by 50% (v/v) and the final ethanol concentration reached 27 g/l.     

Production of ethanol and n-butanol from hexose/pentose mixtures using consecutive fermentations with Saccharomyces cerevisiae and Clostridium acetobutylicum

Summary Saccharomyces cerevisiae and Clostridium acetobutylicum have been used to consecutively ferment molasses (5% solids) containing added pentose sugars (30 g/l). Butanol concentrations of 6.6 g/l and 3.7 g/l have been achieved from L-arabinose and D-xylose, respectively, in the presence of 22 g/l of ethanol.