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1.
Organosolv pretreatment for enzymatic hydrolysis of poplars: I. Enzyme hydrolysis of cellulosic residues 总被引:2,自引:0,他引:2
Chum HL Johnson DK Black S Baker J Grohmann K Sarkanen KV Wallace K Schroeder HA 《Biotechnology and bioengineering》1988,31(7):643-649
Aspen (Populus tremuloides) and black cottonwood (Populus trichocarpa) organosolv pulps produced in a wide range of solvent composition (between 30 and 70% by volume of methanol) and catalysts (H(2)SO(4) and H(3)PO(4)) such that the cooking liquor pH = 3 are easily digested by enzymes. The total yields of hydrolysis residues (pulps) are in the 40-60% range; the acid-catalyzed delignification followed by enzyme hydrolysis can generate 70-88% of the original six-carbon sugars contained in the wood. Glucomannan and arablnogalactan are dissolved into the pulping liquor in the pH range of 2-4.5. Lower pH (=3) leads to additional solubilization of six-carbon sugars. These sugars may be fermented directly. From the insoluble hydrolysis residues, 36-41% conversions of wood into fermentable sugars were obtained after enzyme hydrolysis; the starting feedstocks contain 50.8 and 46.6% hexosans, respectively, for aspen and black cotton-wood. The kinetics of enzymatic hydrolysis of cellulose can be formally treated as two simultaneous pseudo-first-order reactions in which fast and slow hydrolyses of cellulose occur. Correlations between the glucan digestibility and the effect of the pretreatment have been made. The higher residual xylan content reduces the amount of the rapidly hydrolyzable glucan fraction and lowers the glucan digestibility. The proposed simple kinetic treatment is very helpful in assessing the effect of the pretreatment on pulp enzyme hydrolyzability. 相似文献
2.
Codon usage in the vertebrate hemoglobins and its implications 总被引:2,自引:0,他引:2
A study of codon usage in vertebrate hemoglobins revealed an evolutionary
trend toward elevated numbers of CpG codon boundary pairs in mammalian
hemoglobin alpha genes. Selection for CpG codon boundaries countering the
generally observed CpG suppression is strongly suggested by these data.
These observations parallel recently published experimental results that
indicate that constitutive expression of the human alpha-globin gene
appears to be determined by regulatory information encoded within the
structural gene. The possibility is raised that, in the absence of
selection, CpG decay can be used to date the evolutionary origin of a
mammalian alpha pseudogene from its active alpha gene.
相似文献
3.
Evolution of crystallins: expression of lens-specific proteins in the blind mammals mole (Talpa europaea) and mole rat (Spalax ehrenbergi) 总被引:3,自引:0,他引:3
Quax-Jeuken Y; Bruisten S; Bloemendal H; de Jong WW; Nevo E 《Molecular biology and evolution》1985,2(4):279-288
The mole (Talpa europaea; Insectivora) and the mole rat (Spalax ehrenbergi;
Rodentia) both have degenerated eyes as a convergent adaptation to
subterranean life. The rudimentary eye lenses of these blind mammals no
longer function in a visual process. The crystallin genes, which display a
lens-specific expression pattern, were studied in these blind mammals and
in related species with normal eyes by hybridizing their genomic DNAs with
probes obtained from cDNA clones for alpha A-, alpha B-, and beta
Bp-crystallins from calf and gamma 3- crystallin from the rat. For all
crystallin genes examined, the hybridization signals of mole and mole rat
genomic DNA were comparable, respectively, with those of shrew and of rat
and mouse, normal-vision representatives of the orders Insectivora and
Rodentia. The expression of the crystallins at the protein level was tested
by using antiserum specific for alpha-crystallin in immunofluorescence
reactions on lens sections of mole and mole rat eyes and by using antisera
against the beta- and gamma-crystallins on sections of the mole eye. All
antisera gave positive fluorescence reactions exclusively with lens tissue
of these blind mammals, indicating that the crystallins are still normally
expressed despite the fact that these lenses have had no function in a
visual process in these mammals for at least many million years. These
findings apparently imply that some unknown selective advantage has
conserved the crystallin genes and their expression after the loss of
normal function of the lenses.
相似文献
4.
In Drosophila pseudoobscura, the amylase (Amy) multigene family is
contained within a series of inversions, or gene arrangements, on the third
chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL)
inversions are central to the phylogeny of arrangements, and have clusters
of other arrangements derived from them. The gene arrangements belonging to
each of these three clusters have a characteristic number of Amy genes,
ranging from three in ST to two in SC to one in TL. This distribution
pattern can reflect a history of either duplications or deletions, although
the data available in the past did not permit a decision between these
alternatives. We provide unambiguous evidence that three Amy genes were
present before the divergence of the ST, SC, and TL arrangements. Thus, the
current status of the Amy multigene family is the result of deletions in
the TL and SC arrangements, which created three new pseudogenes: TL
Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences
revealed that, in the SC and ST arrangements, pseudogene evolution has been
retarded, most likely due to the homogenization effect of gene conversion.
Finally, by determining the original copy number, we have reconstructed the
evolutionary history of the Amy multigene family and linked it with the
evolution of the central gene arrangements.
相似文献
5.
The alpha-amylase (Amy) multigene family in Drosophila pseudoobscura is
located on the third chromosome, which is polymorphic for more than 40
inverted gene arrangements. The number of copies in this family ranges from
one to three, depending on the arrangement in question. A previous study of
the three Amy genes from the Standard (ST) arrangement suggested either
that duplicated copies (Amy2 and Amy3) are functionally constrained or that
they are undergoing gene conversion with Amy1. In order to elucidate
further the pattern of molecular evolution in this family, we cloned and
sequenced four additional Amy genes, two from the Santa Cruz (SC) and two
from the Chiricahua (CH) gene arrangement. Of the two alternatives, only
the hypothesis of gene conversion is supported by the sequence analysis.
The homogenization effect of gene conversion has been strongest in SC,
whose copies differ by only two nucleotides, less noticeable in ST, and
negligible in the CH. Furthermore, the action of gene conversion is
apparently localized, occurring only in the coding region. Interestingly,
these results concur with the findings of other workers for the duplicated
Amy genes in the Drosophila melanogaster group. Thus, the occurrence of
gene conversion in the Amy multigene family seems to be a common feature in
the Drosophila species studied so far.
相似文献
6.
Eunice Sok Ping Leong Yan Jun Liu Chan Choy Chum Jing Hua Teng 《Plasmonics (Norwell, Mass.)》2013,8(2):1221-1226
Optical magnetic responses were demonstrated in subwavelength Ag–MgF2–Ag grating structures for transverse magnetic-polarized light. The subwavelength Ag–MgF2–Ag grating structures were fabricated using e-beam lithography followed by a lift-off process. By fixing the Ag–MgF2–Ag strip dimension, the effect of the stripe width on the magnetic resonances was compared for two different grating pitches. With further reduced grating pitch, we pushed the optical magnetic resonances to near UV (deep blue). Numerical simulations confirmed our experimental observations and were in good agreement with the experimental results. 相似文献
7.
Aaron P. Chum Sophie R. Shoemaker Patrick J. Fleming Karen G. Fleming 《Protein science : a publication of the Protein Society》2019,28(7):1340-1349
SurA, Skp, FkpA, and DegP constitute a chaperone network that ensures biogenesis of outer membrane proteins (OMPs) in Gram‐negative bacteria. Both Skp and FkpA are holdases that prevent the self‐aggregation of unfolded OMPs, whereas SurA accelerates folding and DegP is a protease. None of these chaperones is essential, and we address here how functional plasticity is manifested in nine known null strains. Using a comprehensive computational model of this network termed OMPBioM, our results suggest that a threshold level of steady state holdase occupancy by chaperones is required, but the cell is agnostic to the specific holdase molecule fulfilling this function. In addition to its foldase activity, SurA moonlights as a holdase when there is no expression of Skp and FkpA. We further interrogate the importance of chaperone–client complex lifetime by conducting simulations using lifetime values for Skp complexes that range in length by six orders of magnitude. This analysis suggests that transient occupancy of durations much shorter than the Escherichia coli doubling time is required. We suggest that fleeting chaperone occupancy facilitates rapid sampling of the periplasmic conditions, which ensures that the cell can be adept at responding to environmental changes. Finally, we calculated the network effects of adding multivalency by computing populations that include two Skp trimers per unfolded OMP. We observe only modest perturbations to the system. Overall, this quantitative framework of chaperone–protein interactions in the periplasm demonstrates robust plasticity due to its dynamic binding and unbinding behavior. 相似文献
8.
Ingo Aldag Ulrike Bockau Jan Rossdorf Sven Laarmann Willem Raaben Lutz Herrmann Thomas Weide Marcus WW Hartmann 《BMC biotechnology》2011,11(1):11
Background
Tetrahymena thermophila possesses many attributes that render it an attractive host for the expression of recombinant proteins. Surface proteins from the parasites Ichthyophthirius multifiliis and Plasmodium falciparum and avian influenza virus antigen H5N1 were displayed on the cell membrane of this ciliate. Furthermore, it has been demonstrated that T. thermophila is also able to produce a functional human DNase I. The present study investigates the heterologous expression of the functional human intestinal alkaline phosphatase (hiAP) using T. thermophila and thereby presents a powerful tool for the optimization of the ciliate-based expression system. 相似文献9.
10.
Electrochemical reductions of iron(II) diimine complexes [FeL32+, where L = CH3NC(R)C(R′) NCH3, aliphatic diimine series with R,R′ = H,H; H,CH3 and CH3,CH3 and L = C5H4NC(R)N(R′), mixed diimine series with R,R′ = H,CH3 and CH3] were investigated through polarography and cyclic voltammetry in acetonitrile, with tetraethylammonium perchlorate supporting electrolyte (0.2 M) as a function of temperature. In the 0 to ?2.4 V vs. Ag/AgCl potential range two to four polarographic waves were observed for the aliphatic series. The first two waves can be described as one-electron reversible reduction processes. They indicate that low valence states iron(I) and iron(0) are stabilized in acetonitrile. In the mixed ligand series three one-electron reversible reduction waves were observed, indicating that in addition to the low valence states stabilized in the aliphatic diimine series the formal reduction state Fe(–I) is also stabilized. The stabilization of the low oxidation states is due to the electron acceptor properties of the diimine ligands, inherent to the presence of the chromophoric iron diimine group. The half-wave potential data and the stabilization of the low valence states point to the importance of analyzing both σ and π effects. The molecular electronegativity values for the series of iron diimine complexes investigated evidences a synergistic interaction between the metal-ligand σ and π bonds. Diffusion coefficients, temperature effects on the heterogeneous electron transfer step, and electrocapillary curves were obtained for these complexes. No evidence for adsorption of the complexes on mercury electrodes was found for the one-electron reversible steps. When comparing polarographic data with those obtained on platinum disk working electrodes employed in the cyclic voltammetric experiments, we observed that for the symmetric aliphatic diimine ligands the observed cathodic currents are larger than expected on the basis of the previously calculated diffusion coefficients. In addition, the reduction waves are shifted 0.14 V to more negative potentials. The symmetric aliphatic diimine complexes exhibit adsorption of the electroactive species on the surface of the platinum electrodes in this potential range. 相似文献