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71.
Impact and efficiency of GH10 and GH11 thermostable endoxylanases on wheat bran and alkali-extractable arabinoxylans 总被引:1,自引:0,他引:1
Beaugrand J Chambat G Wong VW Goubet F Rémond C Paës G Benamrouche S Debeire P O'Donohue M Chabbert B 《Carbohydrate research》2004,339(15):2529-2540
The results of a comparative study of two thermostable (1-->4)-beta-xylan endoxylanases using a multi-technical approach indicate that a GH11 xylanase is more useful than a GH10 xylanase for the upgrading of wheat bran into soluble oligosaccharides. Both enzymes liberated complex mixtures of xylooligosaccharides. 13C NMR analysis provided evidence that xylanases cause the co-solubilisation of beta-glucan, which is a result of cell-wall disassembly. The simultaneous use of both xylanases did not result in a synergistic action on wheat bran arabinoxylans, but instead led to the production of a product mixture whose profile resembled that produced by the action of the GH10 xylanase alone. Upon treatment with either xylanase, the diferulic acid levels in residual bran were unaltered, whereas content in ferulic and p-coumaric acids were unequally decreased. With regard to the major differences between the enzymes, the products resulting from the action of the GH10 xylanase were smaller in size than those produced by the GH11 xylanase, indicating a higher proportion of cleavage sites for the GH10 xylanase. The comparison of the kinetic parameters of each xylanase using various alkali-extractable arabinoxylans indicated that the GH10 xylanase was most active on soluble arabinoxylans. In contrast, probably because GH11 xylanase can better penetrate the cell-wall network, this enzyme was more efficient than the GH10 xylanase in the hydrolysis of wheat bran. Indeed the former enzyme displayed a nearly 2-fold higher affinity and a 6.8-fold higher turnover rate in the presence of this important by-product of the milling industry. 相似文献
72.
M. Abou Hachem S. Bozonnet M. Willemoë s B. Kramh ft K. Fukuda B. C. B nsager M. T. Jensen J. N hr S. Tranier N. Juge X. Robert R. Haser N. Aghajari B. Svensson 《Biocatalysis and Biotransformation》2006,24(1):83-93
-Amylases are endo-acting retaining enzymes of glycoside hydrolase family 13 with a catalytic (β/)8-domain containing an inserted loop referred to as domain B and a C-terminal anti-parallel β-sheet termed domain C. New insights integrate the roles of Ca2 + , different substrates, and proteinaceous inhibitors for -amylases. Isozyme specific effects of Ca2 + on the 80% sequence identical barley -amylases AMY1 and AMY2 are not obvious from the two crystal structures, containing three superimposable Ca2 + with identical ligands. A fully hydrated fourth Ca2 + at the interface of the AMY2/barley -amylase/subtilisin inhibitor (BASI) complex interacts with catalytic groups in AMY2, and Ca2 + occupies an identical position in AMY1 with thiomaltotetraose bound at two surface sites. EDTA-treatment, DSC, and activity assays indicate that AMY1 has the highest affinity for Ca2 + . Subsite mapping has revealed that AMY1 has ten functional subsites which can be modified by means protein engineering to modulate the substrate specificity. Other mutational analyses show that surface carbohydrate binding sites are critical for interaction with polysaccharides. The conserved Tyr380 in the newly discovered 'sugar tongs' site in domain C of AMY1 is thus critical for binding to starch granules. Furthermore, mutations of binding sites mostly reduced the degree of multiple attack in amylose hydrolysis. AMY1 has higher substrate affinity than AMY2, but isozyme chimeras with AMY2 domain C and other regions from AMY1 have higher substrate affinity than both parent isozymes. The latest revelations addressing various structural and functional aspects that govern the mode of action of barley -amylases are reported in this review. 相似文献
73.
DNA ligases are essential guardians of genome integrity by virtue of their ability to recognize and seal 3′-OH/5′-phosphate nicks in duplex DNA. The substrate binding and three chemical steps of the ligation pathway are coupled to global and local changes in ligase structure, involving both massive protein domain movements and subtle remodeling of atomic contacts in the active site. Here we applied solution NMR spectroscopy to study the conformational dynamics of the Chlorella virus DNA ligase (ChVLig), a minimized eukaryal ATP-dependent ligase consisting of nucleotidyltransferase, OB, and latch domains. Our analysis of backbone 15N spin relaxation and 15N,1H residual dipolar couplings of the covalent ChVLig-AMP intermediate revealed conformational sampling on fast (picosecond to nanosecond) and slow timescales (microsecond to millisecond), indicative of interdomain and intradomain flexibility. We identified local and global changes in ChVLig-AMP structure and dynamics induced by phosphate. In particular, the chemical shift perturbations elicited by phosphate were clustered in the peptide motifs that comprise the active site. We hypothesize that phosphate anion mimics some of the conformational transitions that occur when ligase-adenylate interacts with the nick 5′-phosphate. 相似文献
74.
75.
In rain forest, the large numbers of species of fleshy-fruited plants and frugivorous animals result in a large number of potential fruit–frugivore interactions, which are challenging to survey in the field. Yet, knowledge of these relationships is needed to predict consequences of changes in the frugivore assemblage for seed dispersal. In the absence of comprehensive dietary information, it may be possible to delineate between frugivores that disperse different plants using ‘functional traits,’ or morphological and behavioral attributes of frugivores that interact with differences in salient characteristics of plant species. Here we use data on the consumption of 244 Australian rain forest plant species by 38 bird species to test for associations between patterns of frugivory and birds': (1) degree of frugivory, (2) gape width, and (3) seed treatment (seed crushing or seed dispersing). Degree of frugivory and gape width explain 74 percent of the variation in the sizes of fruits consumed by frugivorous birds. Among birds that consume a substantial dietary proportion of fruit, birds with wider gapes consume larger fruits. In contrast, this relationship was not shown by birds for which fruit is only a minor dietary component. Degree of frugivory and gape width, together with seed treatment, also strongly predict the overall taxonomic composition and diversity of plants consumed by bird species. Functional classifications of frugivore species may prove useful in developing a predictive understanding of fruit–frugivore interactions in other rain forest regions where detailed dietary information is not available for most frugivores. 相似文献
76.
Shannon C. Morsello Amanda L. P. Beaudoin Russell L. Groves Brian A. Nault George G. Kennedy 《Entomologia Experimentalis et Applicata》2010,134(3):260-271
Effects of temperature and precipitation on spring dispersal patterns of Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) caught on yellow sticky traps were estimated in central and eastern North Carolina and eastern Virginia, USA, from 1997 to 2001, and in 2004 and 2007. Data were collected from 44 sites within 14 locations over 7 years, resulting in 30 location‐year data combinations. The following independent variables were examined to determine their relationship to the number of F. fusca caught on sticky traps during specified time intervals: cumulative degree days (base 10.5 °C) from 1 November to the start of each trapping interval (DD), number of days with temperatures favorable for flight during each trapping interval (DTFF), and an index of rainfall during specific intervals prior to and during the trapping interval (RI). Regression models that contained various combinations of these variables explained 62, 79, 74, and 68% of the variation in the number of dispersing F. fusca captured during 1–15 April, 16–30 April, 1–15 May, and 16–31 May, respectively. The results provide strong evidence that the suppressive effects of precipitation on growth of local populations developing during late winter and early spring are subsequently manifest at the landscape scale as reductions in the populations of dispersing adults that may persist for as long as 5–6 weeks after the precipitation occurs. 相似文献
77.
S. E. Babina F. V. Tuzikov N. A. Tuzikova V. N. Buneva G. A. Nevinskii 《Molecular Biology》2006,40(1):121-131
Lactoferrin (LF) is a multifunctional acute-phase protein involved in nonspecific defense against bacteria, viruses, and cancer diseases and is present in human barrier fluids, blood, and milk. Small-angle X-ray scattering (SAXS) and light scattering (LS) demonstrated for the first time that LF occurs in the form of oligomers, with a high monomer unit number in the solution. The degree of LF oligomerization depends on the LF concentration and the storage period of non-frozen neutral LF solutions. The average inertial radius of scattering particles (R g) reaches 100–450 Å at LF concentrations comparable with those in human milk, while R g of LF monomers is 26.7 Å. LF forms complexes with various nucleotides and hydrolyzes them. The addition of ATP or AMP to LF solutions accelerates LF oligomerization and increases R g to 600–700 Å, regardless of the initial degree of LF oligomerization. According to the different models (sphere, plate, and cylinder) of LF aggregates, its complexes with such R g presumably contain several tens to thousands of LF monomers. The possible role of oligomeric complexes in multiple biological functions of LF is discussed. 相似文献
78.
Root Morphology and Anchorage of Six Native Tree Species from a Tropical Montane Forest and an Elfin Forest in Ecuador 总被引:1,自引:1,他引:0
Root architecture of tree species was investigated at two different altitudes in tropical forests in Ecuador. Increasing altitude
was accompanied by higher wind speeds and more shallow soils, while slope angles of both sites were comparable (20–50°). Three
tree species typical for the montane forest at 1900 m (Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae), Clethra revoluta (Ruiz & Pav.) Spreng. (Clethraceae), Vismia tomentosa Ruiz & Pav. (Clusiaceae)) and for the elfin forest at 3000 m (Weinmannia loxensis Harling (Cunoniaceae), Clusia spec. (Clusiacaea) Styrax foveolaria Perkins (Styraceae)) were examined. At 1900 m, 92% of the trees grew upright, in comparison to 52% at 3000 m. At 3000 m,
48% of the trees were inclined, lying or even partly uprooted. At this altitude, all trees with tap roots or with shoots connected
by coarse rhizomes, 83% of the trees with stilt roots, and 50% of the trees in which stems or roots were supported by other
trees grew upright, suggesting that these characteristics were relevant for tree stability. Root system morphology differed
markedly between altitudes. In contrast to 1900 m, where 20% of structural roots originated in the deeper mineral soil, root
origin at 3000 m was restricted to the forest floor. The mean ratio of root cross sectional area to tree height decreased
significantly from 6.1 × 10−3 m2 m−1 at 1900 m to 3.2 × 10−3 m2 m−1 at 3000 m. The extent of root asymmetry increased significantly from 0.29 at 1900 m to 0.62 at 3000 m. This was accompanied
by a significantly lower number of dominant roots at 3000 m (2.3 compared to 3.8 at 1900 m). In conclusion, native tree species
growing in tropical montane and elfin forests show a variety of root traits that improve tree stability. Root system asymmetry
is less important for tree stability where anchorage is provided by a deep and solid root–soil plate. When deep rooting is
impeded, root traits improving the horizontal extension of the root–soil plate are more pronounced or occur more frequently.
Furthermore, mutual mechanical support of roots and stems of neighboring trees seems to be an appropriate mechanism to provide
anchorage in soils with low bulk density and in environments with high wind speeds. 相似文献
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