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51.
Starch synthase I (SSI) from various sources has been shown to preferentially elongate branch chains of degree of polymerisation (DP) from 6–7 to produce chains of DP 8–12. In the recently determined crystal structure of barley starch synthase I (HvSSI) a so-called surface binding site (SBS) was seen, which was found by mutational analysis to be essential for the activity of HvSSI on glycogen. We now show in binding studies using surface plasmon resonance that HvSSI has no detectable affinity for malto-triose and -tetraose, but clearly binds maltopentaose, -hexaose, -heptaose (M7) and β-cyclodextrin (β-CD) albeit with a measurable K D for only β-CD and M7. Moreover, an HvSSI SBS mutant F538A lost the ability to bind β-CD and maltooligosaccharides. This behaviour suggests that a chain in the α-glucan molecule (amylopectin) that is undergoing extension attaches itself at the SBS and that the active site itself, likely working on a different end chain, has low affinity for both substrate and product. 相似文献
52.
Roderick A. Capaldi Robert Aggeler Edward P. Gogol Stephan Wilkens 《Journal of bioenergetics and biomembranes》1992,24(5):435-439
The structure of theEscherichia coli ATP synthase has been studied by electron microscopy and a model developed in which the and subunits of the F1 part are arranged hexagonally (in top view) alternating with one another and surrounding a central cavity of around 35 Å at its widest point. The and subunits are interdigitated in side view for around 60 Å of the 90 Å length of the molecule. The F1 narrows and has three-fold symmetry at the end furthest from the F0 part. The F1 is linked to F0 by a stalk approximately 45 Å long and 25–30 Å in diameter. The F0 part is mostly buried in the lipid bilayer. The subunit provides a domain that extends into the central cavity of the F1 part. The and subunits are in a different conformation when ATP+Mg2+ are present in catalytic sites than when ATP+EDTA are present. This is consistent with these two small subunits switching conformations as a function of whether or not phosphate is bound to the enzyme at the position of the phosphate of ATP. We suggest that this switching is the key to the coupling of catalytic site events with proton translocation in the F0 part of the complex. 相似文献
53.
Yago Moises Larrat Francisco Tiago de Vasconcelos Melo Tássia Fernanda Furo Gomes Yuri Wilkens Jeannie Nascimento dos Santos 《Systematic parasitology》2018,95(8-9):871-879
Leptodactylus paraensis Heyer, is a Neotropical anuran species that inhabits Rainforest habitats in the eastern Amazon, but because it has only been recently separated from the Leptodactylus pentadactylus (Laurenti) species group, little is known about its helminth fauna. This study describes a new species of Oswaldocruzia Travassos, 1917 and records the first occurrence of this genus parasitising L. paraensis and the second species for the Caxiuanã National Forest in the eastern Amazon, Brazil. Oswaldocruzia lanfrediae n. sp. is characterised by having an anterior extremity with a smooth cephalic vesicle divided into two portions, a claviform oesophagus, well-developed cuticular longitudinal ridges and lateral alae. Females have a well-developed ovojector, with didelphic and amphidelphic uteri. Males show complex robust spicules divided into a slightly curved shoe, a bifurcated fork and a blade terminating in 2–3 processes. The new species differs from its congeners especially regarding the lateral alae and the morphology of the spicules, in addition to morphometric characters such as body size, oesophagus length, deirid position, nerve-ring position and relative position of the vulva in females. 相似文献
54.
55.
Genetics and hybridization in surface and cave Astyanax (Teleostei): a comparison of regressive and constructive traits 下载免费PDF全文
Horst Wilkens 《Biological journal of the Linnean Society. Linnean Society of London》2016,118(4):911-928
Change in ecological conditions, as seen in surface and cave populations of Astyanax (Teleostei), has caused the divergent evolution of a large number of traits like eyes, coloration, taste, lateral line, and different kinds of behaviour like schooling, sleep or feeding posture. Because of the interfertility of surface and cave forms these fish are an exceptional object to study the morphological and genetic basis of the evolution of such complex regressive and constructive traits. Classical crossing analyses and genomic studies are contributing to growing understanding. Both kinds of traits mostly rely on multiple genetic bases and the phenotypic manifestation in the various crosses is similar. The gene effect underlying the phenotypic manifestation may exhibit an exponential increase at differing amounts in the various traits and crosses. Missing or presence of such genetic interaction helps determine whether the variability of eyes or pigmentation exhibited by Astyanax cave fish populations like Micos, is due to a more recent origin or to secondary hybridization with the surface fish. Neither crossing analysis nor QTL mapping revealed that eye reduction is pleiotropically antagonistically related to the increase of taste buds or lateral line sense. Independent inheritance of traits suggests that Astyanax cave fish are subjected to mosaic evolution. 相似文献
56.
57.
L. A. Wilkens D. F. Russell P. Xing C. Gurgens 《Proceedings. Biological sciences / The Royal Society》1997,264(1389):1723
A novel electrosensory function is presented for the large, plankton-feeding, freshwater paddlefish, Polyodon spathula, along with a hypothesis which accounts for the distinctive, elongated rostrum of this unusual fish. Behavioural experiments conducted in the ''dark'' (under infrared illumination), to eliminate vision, show that paddlefish efficiently capture planktonic prey to distances up to 80–90 mm. They make feeding strikes at dipole electrodes in response to weak low-frequency electrical currents. Fish also avoid metal obstacles placed in the water, again in the dark. Electrophysiological experiments confirm that the Lorenzinian ampullae of paddlefish are sensitive to weak, low-frequency electrical signals, and demonstrate unequivocally that they respond to the very small electrical signals generated by their natural zooplankton prey (Daphnia sp.). We propose that the rostrum constitutes the biological equivalent of an electrical antenna, enabling the fish to accurately detect and capture its planktonic food in turbid river environments where vision is severely limited. The electrical sensitivity of paddlefish to metallic substrates may interfere with their migrations through locks and dams. 相似文献
58.
A differential equation has been derived for the motion of the mechanosensory hairs of animals when they are stimulated by the motion of their fluid environment. Specific solutions of the equation are obtained for three states of fluid flow including steady-state sinusoidal oscillations. The model is specifically applied to crayfish sensilla in an aqueous medium, but the assumptions of the model are also shown to be valid in air for the sensory hairs of insects. The calculations are consistent with available experimental data. 相似文献
59.
Dennis Wilkens Juhl Wilma van Rensburg Xavier Bossis J. Arnold Vosloo Marina Rautenbach Burkhard Bechinger 《Journal of peptide science》2019,25(5)
Tyrocidines are a family of cyclic decapeptides produced by the soil bacterium, Brevibacillus parabrevis. These antibiotic peptides can be used to prevent infections in agriculture and food industry but also to prepare antimicrobial lozenges, creams, and dressings for medical applications. It has been observed that the tyrocidines interact with saccharides such as cellulose from their soil environment, as well as sugars in culture media and glycans in fungal cell walls. Here, we investigated the interactions of tyrocidines with glucose, sucrose, and cellotetraose (as cellulose model) in a quantitative fashion utilising CD and NMR spectroscopy. The CD and NMR spectra of tyrocidine A (TrcA) were analysed as a function of solvent composition, and the spectral properties agree with the formation of oligomeric structures that are governed by β‐sheet secondary structures once the acetonitrile content of the solvent is increased. Saccharides seem to also induce TrcA spectral changes reverting those induced by organic solvents. The CD spectral changes of TrcA in the presence of glucose agree with new ordered H‐bonding, possibly β‐sheet structures. The amides involved in intramolecular H‐bonding remained largely unaffected by the environmental changes. In contrast, amides exposed to the exterior and/or involved in TrcA intermolecular association show the largest 1H chemical shift changes. CD and NMR spectroscopic investigations correlated well with TrcA‐glucose interactions characterized by a dissociation constant around 200 μM. Interestingly, the association of cellotetraose corresponds closely to the additive effect from four glucose moieties, while a much higher dissociation constant was observed for sucrose. Similar trends to TrcA for binding to the three saccharides were observed for the analogous tyrocidines, tyrocidine B, and tyrocidine C. These results therefore indicate that the tyrocidine interactions with the glucose monosaccharide unit are fairly specific and reversible. 相似文献
60.
Ringel AK Wilkens E Hortig D Willke T Vorlop KD 《Applied microbiology and biotechnology》2012,93(3):1049-1056
A new screening method was developed and established to find high-performance bacteria for the conversion of crude glycerol
to 1,3-propanediol. Three soil samples from palm oil-rich habitats were investigated using crude glycerol of a German biodiesel
plant. Nine promising 1,3-propanediol producers could be found. Because of a special pH buffer system, a fast evaluation on
microscale and high 1,3-propanediol concentrations up to 40 g L−1 could be achieved. Three strains demonstrated very high product tolerance and were identified as Clostridium butyricum. Two strains, AKR91b and AKR102a, grew and produced 1,3-propanediol in the presence of 60 g L−1 initial 1,3-propanediol, the strain AKR92a even in the presence of 77 g L−1 1,3-propanediol. The strains AKR91b and AKR102a tolerated up to 150 g L−1 crude glycerol and produced 80% of the 1,3-propanediol attained from pure glycerol of the same concentration. Further criteria
for the choice of a production strain were the pathogenicity (risk class), ability to grow on low-cost media, e.g., with less
yeast extract, and robustness, e.g., process stability after several bioconversions. Overall, the strain C. butyricum AKR102a was chosen for further process optimization and scale-up due to its high productivity and high final concentration
in a pH-regulated bioreactor. 相似文献