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1.
A thermosensitive uracil requiring mutant of Bacillus subtilis Marburg 168 thy trp 2 ts42 was examined as to the colony forming ability at the permissive and nonpermissive temperatures. The viability of the mutant cells decreased rapidly at the restrictive temperature in the modified Woese’s (MW) medium. However, the cells retained viability when sodium succinate or potassium chloride was added to the medium at that temperature although uracil deficiency was unchanged. A little but significant incorporation of adenine-8- 14C into RNA still continued even after the incorporation of N-acetyl- 3H- d-glucosamine into acid insoluble fraction of the cells terminated in the MW medium at 48°C. Both incorporations as well as increase of absorbance were slowed down in the presence of sodium succinate at 48°C. This mutant, ts42, was more sensitive to deoxycholate (DOC) than the parent strain. The restoration of colony forming ability after the temperature shift back from 48 to 37°C was suppressed by the addition of DOC to the medium. However, the cell became resistant to DOC when uracil was added to the medium prior to the temperature shift. 相似文献
3.
Oleogels based on three different oils (sunflower oil, solid coconut oil and liquid coconut oil) were formulated using β-sitosterol. In general, an observed increase in crystallinity was correlated with an increase in the gel storage modulus and hardness. Addition of lecithin promoted the formation of needle-like crystals of β-sitosterol with a corresponding increase in strain tolerance and oil-trapping capacity for oleogels produced with liquid oils. However, the incorporation of β-sitosterol crystals with or without lecithin into oleogels containing solid coconut oil reduced its strain tolerance by interrupting the formation of continual radiolitic crystal structures. The use of sunflower oil (long chain fatty acids) was more favourable to the packing and growth of gelator crystals and the formation of an elastic gel, in comparison to liquid coconut oil (short chain fatty acids). Overall, the type and physical state of oil influence the formation of oil crystal network, thus affecting its gel properties. These findings allow the better understanding of β-sitosterol-based oleogels, providing opportunity to design for the application as a fat-replacer and lowering solid fat content. 相似文献
4.
The milk protein β-lactoglobulin (βLG) dominates the properties of whey aggregates in food products. Here we use spectroscopic and calorimetric techniques to elucidate how anionic, cationic and non-ionic surfactants interact with bovine βLG and modulate its heat-induced aggregation. Alkyl trimethyl ammonium chlorides (xTAC) strongly promote aggregation, while sodium alkyl sulfates (SxS) and alkyl maltopyranosides (xM) reduce aggregation. Sodium dodecyl sulfate (SDS) binds to non-aggregated βLG in several steps, but reduction of aggregation was associated with the first binding step, which occurs far below the critical micelle concentration. In contrast, micellar concentrations of xMs are required to reduce aggregation. The ranking order for reduction of aggregation (normalized to their tendency to self-associate) was C10-C12>C8>C14 for SxS and C8>C10>C12>C14>C16 for xM. xTAC promote aggregation in the same ranking order as xM reduce it. We conclude that SxS reduce aggregation by stabilizing the protein's ligand-bound state (the melting temperature t(m) increases by up to 10°C) and altering its charge potential. xM monomers also stabilize the protein's ligand-bound state (increasing t(m) up to 6°C) but in the absence of charged head groups this is not sufficient by itself to prevent aggregation. Although micelles of both anionic and non-ionic surfactants destabilize βLG, they also solubilize unfolded protein monomers, leaving them unavailable for protein-protein association and thus inhibiting aggregation. Cationic surfactants promote aggregation by a combination of destabilization and charge neutralization. The food compatible surfactant sodium dodecanoate also inhibited aggregation well below the cmc, suggesting that surfactants may be a practical way to modulate whey protein properties. 相似文献
5.
The two spotted spider mite, Tetranychus urticae Koch, is an important herbivore pest of apple trees in Northwest China. This spider mite and another less damaging spider mite, Eotetranychus pruni Oudemans, are attacked by a common and often effective phytoseiid predator, Euseius finlandicus (Oudemans). Functional relationships were studied in the field to evaluate the impact of E. pruni and E. finlandicus on T. urticae. The results from this study showed that the predator-mediated apparent competition strongly affected the population dynamics of T. urticae. The addition of the apparent competitor E. pruni alone had little impact on T. urticae densities. Although the release of the predator E. finlandicus alone could result in reduction in T. urticae densities, the greatest reduction in T. urticae densities occurred in plots where both the predator E. finlandicus and apparent competitor E. pruni were released. In apple orchards, the early introduction of both the apparent competitor E. pruni and predator E. finlandicus would evidently increase the population size of the predator E. finlandicus and consequently significantly enhance the control of T. urticae populations. It is concluded from the study that the predator and apparent competitor release might be an appropriate control for the target species. 相似文献
9.
1 IntroductionInthenaturemanyanimals ,suchas geckoes ,flies ,bees ,locustsandspiders ,haveamagicabilitytomoveorholdonvarioussurfaces roughorsmoothfloors ,wallsorceilings.Themechanism ,howtheani malsattachto ,holdonanddetachfromthesurfaces ,mayenlightenusonwall climbingrobotsformthefeetdesign .Therobotsaregreatlyindemandinvacuumcircumstance ,insurvivorsearchinginflown downbuildingandinpipelineinspectingandrepairing .Themechanismsmayalsoshowushowtodesignhighadap tivemanipulators.Thebionicfeetd… 相似文献
10.
Bioassays with Bacillus thuringiensis var. galleriae Berliner -endotoxin and plant phenolics on Heliothis armigera Hübner enhanced the activity of B.t. var. galleriae endotoxin. The presence of plant phenolics with B.t var. galleria endotoxin not only reduced feeding potential and weight gain by the larvae, but also enhanced the LC50 value of the toxin. Our study demonstrates the effect of phytochemicals from resistant crop plants on the biocidal activity of B. thuringiensis strains in laboratory conditions. 相似文献
11.
Synthetic 3-aminoharman and 3-aminonorharman (amino-β-carbolines) caused slight but definite induction of sister-chromatid exchanges (SCEs) in human lymphoblastoid cells NL3 and Chinese hamster cells CHO-K1. These amino-β-carbolines are ranked between 2-amino-α-carboline and 2-amino-6-methyl-9a-aza-δ-carboline (Glu-P-2) and much lower than 3-amino-γ-carbolines (Trp-P-1 and 2) in inductive activity. 1-Amino-β-carboline, harman and norharman had very weak, if any, SCE-inducer activity.Norharman had a synergistic effect with aromatic amines such as Trp-P-2 and aniline on SCE induction, while 3-aminoharman suppressed SCE induction by more potent inducers such as Trp-P-2 and benzo[ a]pyrene. 相似文献
13.
The effect of aluminum ions on the binding properties of α-chymotrypsin has been studied. The results show that aluminum
does not affect the catalytic rate constant k
cat, but it acts as an enzyme activator favoring the binding of the substrate to the catalytic site (i.e. decreasing K
m). Furthermore, aluminum binding to α-chymotrypsin displays about a threefold decrease in its affinity for the macromolecular
inhibitor bovine pancreatic trypsin inhibitor (BPTI). Altogether, the different effect of aluminum on the binding of synthetic
substrates (e.g. N-α-benzoyl- l-tyrosine ethyl ester, BTEE) and macromolecular inhibitors (e.g. BPTI) to α-chymotrypsin suggests the occurrence of an aluminum-linked
conformational change in the enzyme molecule which brings about a marked structural change at the primary and secondary recognition
sites for substrates and inhibitors. The modulative effect exerted by aluminum on the enzyme hydrolytic activity has been
investigated also as a function of pH. The ion-linked effect appears to be dependent on the pH in a complex fashion, which
suggests that aluminum binding is controlled by the protonation of at least two classes of residues on the enzyme molecule.
Received: 5 December 1996 / Accepted: 11 March 1997 相似文献
14.
We have demonstrated that prolactin inhibits gonadotropin-induced ovulation in PMSG-primed mice.The number of ova in oviducts considerably decreased in the group of hCG plus prolactin (PRL)(19.7 + 4.9) as compared with that of hCG alone (31.7 + 6.7). PRL inhibition of hCG-inducedovulation in mice may be through decreasing the ovarian plasminogen activator (PA) activity on onehand, and inhibiting the preovulatory increase in estrogen (E) secretion on the other. 相似文献
15.
Small β-hairpin peptides have been widely used as models for the folding of β-sheets. But how applicable is the folding of such models to β-structure in larger proteins with conventional hydrophobic cores? Here we present multiple unfolding simulations of three such proteins that contain the WW domain double hairpin β-sheet motif: cold shock protein A (CspA), cold shock protein B (CspB) and glucose permease IIA domain. We compare the behavior of the free motif in solution and in the context of proteins of different size and architecture. Both Csp proteins lost contacts between the double-hairpin motif and the protein core as the first step of unfolding and proceeded to unfold with loss of the third β-strand, similar to the isolated WW domain. The glucose permease IIA domain is a larger protein and the contacts between the motif and the core were not lost as quickly. Instead the unfolding pathway of glucose permease IIA followed a different pathway with β1 pulling away from the sheet first. Interestingly, when the double hairpin motif was excised from the glucose permease IIA domain and simulated in isolation in water it unfolded by the same pathway as the WW domain, indicating that it is tertiary interactions with the protein that alter the motif’s unfolding not a sequence dependent effect on its intrinsic unfolding behavior. With respect to the unfolding of the hairpins, there was no consistent order to the loss of hydrogen bonds between the β-strands in the hairpins in any of the systems. Our results show that while the folding behavior of the isolated WW domain is generally consistent with the double hairpin motif’s behavior in the cold shock proteins, it is not the case for the glucose permease IIA domain. So, one must be cautious in extrapolating findings from model systems to larger more complicated proteins where tertiary interactions can overwhelm intrinsic behavior. 相似文献
18.
As determined by analytical ultracentrifugation, purified α-actinin does not form stable complexes with G-actin, myosin, tropomyosin, or the tropomyosintroponin complex. However, α-actinin forms a stable complex with F-actin polymerized either in 100 mM KC1 or in 2mM MgCl 2 without KCl. Viscosity studies confirm that α-actinin interacts as strongly with Mg 2+-polymerized actin as it does with KCl-polymerized actin. 相似文献
20.
By spectrofluorophotometric investigation on various kinds of Saké it was found that they have at least two kinds of fluorescent colors, the one is blue, the other yellowish green. The former is always more dominant than the latter, but is unstable although the intensities of both color decrease remarkably by treatment of active charcoal. Ferulic acid and harman as the blue fluorescent components are isolated, the former from Saké in young, the latter from Saké kept for a long time under direct sun light. 相似文献
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