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311.
Techno-economic evaluation of producing ethanol from softwood: comparison of SSF and SHF and identification of bottlenecks 总被引:4,自引:0,他引:4
The aim of the study was to evaluate, from a technical and economic standpoint, the enzymatic processes involved in the production of fuel ethanol from softwood. Two base case configurations, one based on simultaneous saccharification and fermentation (SSF) and one based on separate hydrolysis and fermentation (SHF), were evaluated and compared. The process conditions selected were based mainly on laboratory data, and the processes were simulated by use of Aspen plus. The capital costs were estimated using the Icarus Process Evaluator. The ethanol production costs for the SSF and SHF base cases were 4.81 and 5.32 SEK/L or 0.57 and 0.63 USD/L (1 USD = 8.5SEK), respectively. The main reason for SSF being lower was that the capital cost was lower and the overall ethanol yield was higher. A major drawback of the SSF process is the problem with recirculation of yeast following the SSF step. Major economic improvements in both SSF and SHF could be achieved by increasing the income from the solid fuel coproduct. This is done by lowering the energy consumption in the process through running the enzymatic hydrolysis or the SSF step at a higher substrate concentration and by recycling the process streams. Running SSF with use of 8% rather than 5% nonsoluble solid material would result in a 19% decrease in production cost. If after distillation 60% of the stillage stream was recycled back to the SSF step, the production cost would be reduced by 14%. The cumulative effect of these various improvements was found to result in a production cost of 3.58 SEK/L (0.42 USD/L) for the SSF process. 相似文献
312.
A number of filamentous fungi are known to produce high levels of saline-soluble and low-molecular-mass lectins. The function of these proteins are not clear but it has been proposed that they are involved in storage of nutrients, development, recognition of other organisms, and defense reactions. A gene encoding such a lectin (AOL) was deleted in the nematode-trapping fungus Arthrobotrys oligospora by homologous recombination. The deletion mutants did not express any hemagglutinating activity or protein cross-reacting with AOL antibodies. There were no significant differences between the DeltaAOL and wild-type strains in spore (conidia) germination, saprophytic growth, and pathogenicity. Furthermore, there was no significant difference in the growth and reproduction of collembolan feeding on the various strains of A. oligospora. Thus either the previous proposed functions of AOL are not correct, or the fungus can compensate for the absence of the lectin by expressing other proteins with similar function(s) as AOL. 相似文献
313.
Background
Contrary to other areas of sequence analysis, a measure of statistical significance of a putative gene has not been devised to help in discriminating real genes from the masses of random Open Reading Frames (ORFs) in prokaryotic genomes. Therefore, many genomes have too many short ORFs annotated as genes. 相似文献314.
Oxidative stress in Caenorhabditis elegans: protective effects of superoxide dismutase/catalase mimetics 总被引:3,自引:1,他引:2
The lifespan of Caenorhabditis elegans can be extended by the administration of synthetic superoxide dismutase/catalase mimetics (SCMs) without any effects on development or fertility. Here we demonstrate that the mimetics, Euk-134 and Euk-8, confer resistance to the oxidative stress-inducing agent, paraquat and to thermal stress. The protective effects of the compounds are apparent with treatments either during development or during adulthood and are independent of an insulin/IGF-I-like signalling pathway also known to affect thermal and oxidative stress resistance. Worms exposed to the compounds do not induce a cellular stress response and no detrimental effects are observed. 相似文献
315.
Primary amines covalently bonded to the surface of poly(dimethylsiloxane) were obtained by hydrosilylation grafting of aminopropyl vinyl ether to Si-H groups formed during argon plasma treatment. The amine groups were derivatized using pentafluorobenzaldehyde and characterized by X-ray photoelectron spectroscopy. The graft yield was about 3% grafted molecules within the depth of the analysis. The terminal aldehyde groups of diazotized heparin was also coupled to the primary amines. This led to a silicone elastomer with covalently bonded heparin which was expected to be hydrolytically stable. This method of bonding primary amines to the surface of silicone elastomers and the subsequent coupling of aldehyde-containing molecules is a promising way of obtaining novel biomaterials. 相似文献
316.
Kennergren C Mantovani V Strindberg L Berglin E Hamberger A Lonnroth P 《American journal of physiology. Endocrinology and metabolism》2003,284(4):E788-E794
The interstitial fluid of the human myocardium was monitored in 13 patients undergoing aortic valve and/or bypass surgery before, during, and after hypothermic potassium cardioplegia. The regulation of glucose and lactate was studied after sampling with microdialysis. The following questions were addressed. 1). Is the rate of transcapillary diffusion the limiting step for myocardial uptake of glucose before or after cardioplegia? 2). Does cold potassium cardioplegia induce a critical deprivation of glucose and/or accumulation of lactate in the myocardium? Before cardioplegia, interstitial glucose was approximately 50% of the plasma level (P < 0.001). Interstitial glucose decreased significantly immediately after induction of cardioplegia and remained low (1.25 +/- 0.25 mM) throughout cardioplegia. It was restored to precardioplegic levels 1 h after release of the aortic clamp. Interstitial glucose then decreased again at 25 and 35 h postoperatively to the levels observed during cardioplegia. Interstitial lactate decreased immediately after induction of cardioplegia but returned to basal level during the clamping period. At 25 and 35 h, interstitial lactate was significantly lower than before and during cardioplegia. Glucose transport over the capillary endothelium is considered rate limiting for its uptake in the working heart but not during cold potassium cardioplegia despite the glucose deprivation following perfusion of glucose-free cardioplegic solution. Lactate accumulated during cardioplegia but never reached exceedingly high interstitial levels. We conclude that microdialysis provides information that may be relevant for myocardial protection during open-heart surgery. 相似文献
317.
The mechanism of prokaryotic chromosome segregation is not known. MreB, an actin homolog, is a shape-determining factor in rod-shaped prokaryotic cells. Using immunofluorescence microscopy we found that MreB of Escherichia coli formed helical filaments located beneath the cell surface. Flow cytometric and cytological analyses indicated that MreB-depleted cells segregated their chromosomes in pairs, consistent with chromosome cohesion. Overexpression of wild-type MreB inhibited cell division but did not perturb chromosome segregation. Overexpression of mutant forms of MreB inhibited cell division, caused abnormal MreB filament morphology and induced severe localization defects of the nucleoid and of the oriC and terC chromosomal regions. The chromosomal terminus regions appeared cohered in both MreB-depleted cells and in cells overexpressing mutant forms of MreB. Our observations indicate that MreB filaments participate in directional chromosome movement and segregation. 相似文献
318.
Recent advances in brain imaging techniques, including functional magnetic resonance imaging (fMRI), offer great promise for noninvasive mapping of brain function. However, the indirect nature of the imaging signals to the underlying neural activity limits the interpretation of the resulting maps. The present report represents the first systematic study with sufficient statistical power to quantitatively characterize the relationship between changes in blood oxygen content and the neural spiking and synaptic activity. Using two-dimensional optical measurements of hemodynamic signals, simultaneous recordings of neural activity, and an event-related stimulus paradigm, we demonstrate that (1) there is a strongly nonlinear relationship between electrophysiological measures of neuronal activity and the hemodynamic response, (2) the hemodynamic response continues to grow beyond the saturation of electrical activity, and (3) the initial increase in deoxyhemoglobin that precedes an increase in blood volume is counterbalanced by an equal initial decrease in oxyhemoglobin. 相似文献
319.
Grigelioniene G Eklöf O Ivarsson SA Westphal O Neumeyer L Kedra D Dumanski J Hagenäs L 《Human genetics》2000,107(2):145-149
Dyschondrosteosis (DCO) and hypochondroplasia (HCH) are common skeletal dysplasias characterized by disproportionate short stature. The diagnosis of these conditions might be difficult to establish especially in early childhood. Point mutations and deletions of the short stature homeobox containing gene (SHOX) are detected in DCO and idiopathic short stature with some rhizomelic body disproportion, whereas mutations in the fibroblast growth factor receptor 3 (FGFR3) gene are found in 40-70% of HCH cases. In this study, we performed mutational analysis of the coding region of the SHOX gene in five DCO and 18 HCH patients, all of whom tested negative for the known HCH-associated FGFR3 mutations. The polymorphic CA-repeat analysis, direct sequencing and Southern blotting were used for detection of deletions and point mutations. The auxological and radiological phenotype of these patients was carefully determined. Three novel mutations in DCO patients were found: (1) a deletion of one base (de1272G) (according to GenBank accession nos. Y11536, Y11535), resulting in a premature stop codon at position 75 of the amino acid sequence; (2) the transversion C485G resulting in the substitution Leu132Val; and (3) the transversion G549T causing an Arg153Leu substitution. These substitutions segregate with the DCO phenotype and affect evolutionarily conserved homeodomain residues, based on a comparison of homeobox containing proteins in 13 species. Moreover, these changes were not found in 80 unrelated, unaffected individuals. This strongly suggests that these mutations are pathogenic. The phenotype of our patients with DCO and HCH varied from mild to severe shortness and body disproportion. These results further support clinical and genetic heterogeneity of dyschondrosteosis and hypochondroplasia. 相似文献
320.
Anders ?stin Mariusz Kowalyczk Rishikesh P. Bhalerao G?ran Sandberg 《Plant physiology》1998,118(1):285-296
The metabolism of indole-3-acetic
acid (IAA) was investigated in 14-d-old Arabidopsis plants grown in
liquid culture. After ruling out metabolites formed as an effect of
nonsterile conditions, high-level feeding, and spontaneous
interconversions, a simple metabolic pattern emerged. Oxindole-3-acetic
acid (OxIAA), OxIAA conjugated to a hexose moiety via the carboxyl
group, and the conjugates indole-3-acetyl aspartic acid (IAAsp) and
indole-3-acetyl glutamate (IAGlu) were identified by mass spectrometry
as primary products of IAA fed to the plants. Refeeding experiments
demonstrated that none of these conjugates could be hydrolyzed back to
IAA to any measurable extent at this developmental stage. IAAsp was
further oxidized, especially when high levels of IAA were fed into the
system, yielding OxIAAsp and OH-IAAsp. This contrasted with the
metabolic fate of IAGlu, since that conjugate was not further
metabolized. At IAA concentrations below 0.5 μm, most of
the supplied IAA was metabolized via the OxIAA pathway, whereas only a
minor portion was conjugated. However, increasing the IAA
concentrations to 5 μm drastically altered the metabolic
pattern, with marked induction of conjugation to IAAsp and IAGlu. This
investigation used concentrations for feeding experiments that were
near endogenous levels, showing that the metabolic pathways controlling
the IAA pool size in Arabidopsis are limited and, therefore, make good
targets for mutant screens provided that precautions are taken to avoid
inducing artificial metabolism.The plant hormone IAA is an important signal molecule in the
regulation of plant development. Its central role as a growth regulator
makes it necessary for the plant to have mechanisms that strictly
control its concentration. The hormone is believed to be active
primarily as the free acid, and endogenous levels are controlled in
vivo by processes such as synthesis, oxidation, and conjugation. IAA
has been shown to form conjugates with sugars, amino acids, and small
peptides. Conjugates are believed to be involved in IAA transport, in
the storage of IAA for subsequent use, in the homeostatic control of
the pool of the free hormone, and as a first step in the catabolic
pathways (Cohen and Bandurski, 1978; Nowacki and Bandurski, 1980;
Tuominen et al., 1994; Östin et al., 1995; Normanly, 1997). It is
generally accepted that in some species conjugated IAA is the major
source of free IAA during the initial stages of seed germination (Ueda
and Bandurski, 1969; Sandberg et al., 1987; Bialek and Cohen, 1989),
and there is also evidence that in some plants (but not all; see Bialek
et al., 1992), the young seedling is entirely dependent on the release
of free IAA from conjugated pools until the plant itself is capable of
de novo synthesis (Epstein et al., 1980; Sandberg et al., 1987).The function of conjugated IAA during vegetative growth is somewhat
less clear. It has been shown that conjugated IAA constitutes as much
as 90% of the total IAA in the plant during vegetative growth
(Normanly, 1997). However, the role of the IAA conjugates at this stage
of the plant''s life cycle remains unknown. Analysis of endogenous IAA
conjugates in vegetative tissues has revealed the presence of a variety
of different compounds, including indole-3-acetyl-inositol,
indole-3-acetyl-Ala, IAAsp, and IAGlu (Anderson and Sandberg, 1982;
Cohen and Baldi, 1983; Chisnell, 1984; Cohen and Ernstsen, 1991;
Östin et al., 1992). Studies of vegetative tissues have indicated
that IAAsp, one of the major conjugates in many plants, is the first
intermediate in an irreversible deactivation pathway (Tsurumi and Wada,
1986; Tuominen et al., 1994; Östin, 1995). Another mechanism that
is believed to be involved in the homeostatic control of the IAA pool
is catabolism by direct oxidation of IAA to OxIAA, which has been shown
to occur in several plant species (Reinecke and Bandurski, 1983;
Ernstsen et al., 1987).One area in the study of IAA metabolism in which our knowledge is
increasing is the analysis of the homeostatic controls of IAA levels in
plants. It has been possible, for instance, to increase the levels of
IAA in transgenic plants expressing iaaM and iaaH
genes from Agrobacterium tumefaciens. Analysis of these
transgenic plants has indicated that plants have several pathways that
can compensate for the increased production of IAA (Klee et al., 1987;
Sitbon, 1992). It is expected that future studies using now-available
genes will provide further insight into IAA metabolism. For example, a
gene in maize encoding IAA-Glc synthetase has been identified, and
several genes (including ILR1, which may be involved
in hydrolysis of the indole-3-acetyl-Leu conjugate) have been cloned
from Arabidopsis (Szerszen et al., 1994; Bartel and Fink,
1995). Furthermore, Chou et al. (1996) identified a gene that
hydrolyzes the conjugate IAAsp to free IAA in the bacterium
Enterobacter aggloremans.Because of its small genome size, rapid life cycle, and the ease of
obtaining mutants, Arabidopsis is increasingly used as a
genetic model system to investigate various aspects of plant growth and
development. IAA signal transduction is also being investigated
intensively in Arabidopsis in many laboratories (Leyser, 1997). Mutants
with altered responses to externally added auxins or IAA conjugates
have been identified in Arabidopsis. The identified mutants are either
signal transduction mutants such as axr1-4 (Lincoln et al.,
1990), or have mutations in genes involved in auxin uptake or
transport, such as aux1 and pin1 (Okada et al.,
1991; Bennett et al., 1996). A few mutants that are unable to regulate
IAA levels or are unable to hydrolyze IAA conjugates, sur1-2
and ilr1, respectively, have also been identified (Bartel
and Fink, 1995; Boerjan et al., 1995). To our knowledge, no mutant that
is auxotrophic for IAA has been identified to date, which may
reflect the redundancy in IAA biosynthetic pathways or the lethality of
such mutants.In spite of the work reported thus far, many aspects of the metabolism
of IAA in Arabidopsis require further investigation, because few
details of the processes involved in IAA regulation are known. This
lack of knowledge puts severe constraints on genetic analysis of IAA
metabolism in Arabidopsis. For example, it is essential to have prior
knowledge of IAA metabolism to devise novel and relevant screens with
which to identify mutants of IAA metabolism. We have sought to address
this issue by identifying the metabolic pathways involved in catabolism
and conjugation under conditions that minimally perturb physiological
processes. In this investigation we studied the conjugation and
catabolic pattern of IAA by supplying relatively low levels of labeled
IAA and identifying the catabolites and conjugates by MS. Different
feeding systems were tested to optimize the application of IAA and to
avoid irregularities in metabolism attributable to culturing, feeding
conditions, or microbial activity. It is well documented that IAA
metabolism is altered according to the amount of exogenous auxin
applied; therefore, we placed special emphasis on distinguishing
between catabolic routes that occur at near-physiological
concentrations and those that occur at the high auxin concentrations
commonly used in mutant screens. 相似文献