The Y-base of yeast tRNAPhe was replaced by the fluorophores 1-aminoanthracene or proflavine to yield derivatives which are active in all of the reactions of peptide elongation on reticulocyte ribosomes. The relatively long lifetime, higher quantum yield, and environmental sensitivity of 1-aminoanthracene make it a particulary useful adjunct to the Y-base in studying conformational changes in the anticodon region. The absorption and emission spectra of 1-aminoanthracene in tRNA in solutions in which it is active in peptide synthesis indicate that the probe is in a hydrophobic environment, apparently provided by stacking with the adjacent bases in the anticodon loop. The proflavine derivative, tRNA, was employed in iodide quenching, D2O enhancement, and fluorescence depolarization experiments. The results indicate that the fluorophore in partially but not completely protected from the solvent. Anisotropy studies indicate that in solutions approximating those which support peptide synthesis on ribosomes, the probes have significant but restricted flexibility within the anticodon loop. Considered with nmr data and Y-base fluorescence from crystals of tRNA, the results indicate that the solution and crystal structures of tRNAPhe are very similar. In turn, fluorescene from modified tRNAPhe bound to ribosomes is similar to that observed in solution. It is of special significance for future experiments involving nonradiative energy transfer that these probles adjacent to the anticodon retain independent flexibility when bound to ribosomes with poly(U). The tRNAPhe itself appears to be held rigidly on the ribosomes. It is concluded that within the limits dictated by the position and sensitivity of the probes used in this study, the mechanism of tRNAPhe binding to ribosomes and the movement of tRNA and mRNA during the translocation steps of peptide synthesis can be interpreted in terms of the well-defined crystal structure of tRNAPhe. 相似文献
In this paper we consider the following nested random effect model where the αi's, the βij's and the eijk are independent random variables. By assuming that these variables follow a mixture of two normal densities, we study the effects of departure from normality on the classical JT-tests for variance components. It is shown that the departure from normality has little effects on the type 1 error and the power function; this indicates that the classical F-tests are quite robust with respect to departure from normality. 相似文献
Intensity fluctuations of laser light scattered from filamentous viruses Pf1 [length L (Å) × diameter d (Å) = 20,000 × 90], M13 (9000 × 90), potato virus X (5150 × 130), and tobacco mosaic virus (3000 × 180) in sucrose density gradients were measured with a photon correlation spectrometer over a range of scattering angles from 15° to 120°. The experimental data can be approximated by two exponential decays, “slow” and “fast.” The slow decay rate constant t corresponds to the translational diffusion D of the virus, i.e., t = K2D, where K is the magnitude of the scattering vector. The amplitude of the slow component, i.e., translational diffusion, remains greater than that of the fast component, even at high KL. The fast decay rate constant t is also proportional to K2 for viruses such as Pf1, M13, and even potato virus X. In the companion paper, we shall attribute the amplitude enhancement of the translational diffusion to the coupling of its anisotropy to the rotational diffusion modes. In order to explain the excessive decay rates in the fast component, we need to consider the bending mode of rodlike viruses, especially in the longer viruses such as M13 and Pf1, in addition to the usually expected rotational diffusion modes. 相似文献
The dissaccharide D-galactosyl-3-deoxy-D-manno-2-octulosonic acid (Gal-KDO) from lipopolysaccharides (LPS) of the inner core region of the rough mutant EH100 of E. coli 0100 was isolated after mild acid hydrolysis of LPS by means of dialysis, ion-exchange chromatography, gelfiltration and high-voltage paper electrophresis. By chemical analysis galactose and KDO were identified in a molar ratio of approximately 1 : 1. 13C-NMR and 1H-NMR studies, methylation analysis and GLC of the acetylated R.( – )-2-butyl-galactoside identified the structure . 相似文献
Consider the mixed model where xijk's are known constants, βk are unknown parameters and ai, eij are random variables independently and normally distributed with zero means and variances σdi and σ2 respectively, where it is assumed that the di's are known (di >0). This paper presents procedures for estimating the variance components σ, σ2, for testing the hypothesis σ = 0, and for making transformations to random variables with uncorrelated errors and constant variances in order to estimate as well as to test hypothesis concerning the βk's in the model. 相似文献
The dependency of the velocity of biological processes from the temperature is described by the “Law of absolute velocity of biological processes”, which has only the individual parameters energy of activation ΔE, and the universal constant C. The law holds for all biological processes and is expressed by the equation: where C is: . 相似文献
The allowed conformations of the μ-receptor-selective cyclic opioid peptide analog were determined using a grid search through the entire conformational space. Energy minimization of the 13-membered ring structure lacking the exocyclic Tyr1 residue and the Phe3 side chain using the molecular mechanics program Maximin resulted in only four low-energy conformations. These four ring structures served as templates for a further energy minimization study with the Tyr1 residue and Phe3 side chain added to the molecule. The results indicated that the Tyr1 and Phe3 side chains enjoy considerable orientational freedom, but nevertheless, only a limited number of low-energy side-chain configurations were found. The obtained low-energy conformers are discussed in relation to various proposed models of the bioactive conformation of enkephalins and morphiceptin. 相似文献
Abstract: We surveyed drumming ruffed grouse (Bonasa umbellus) to estimate the probability of detecting an individual, and we used Bayesian model selection to assess the influence of factors that may affect detection probabilities of drumming grouse. We found the average probability of detecting a drumming ruffed grouse during a daily survey was 0.33. The probability of detecting a grouse was most strongly influenced by the temperature change during a survey (temp change = 0.23, 95% probability interval [PI] = 0.13 ≤ ≤ 0.33) and its interaction with temperature at the start of the survey (interaction = 0.01, 95% PI = 1.42 × 10−3 ≤ ≤ 0.03). Although the best model also included a main effect of temperature at the start of surveys, this variable did not strongly correlate with detection probabilities (starttemp = −0.03, 95% PI = −0.06 ≤ ≤ 9.80 × 10−5). Model assessment using data collected at other sites indicated that this best model performed adequately (i.e., positive correlation between observed and predicted values) but did not explain much of the variation in detection rates. Our results are useful for understanding the historical drumming index used to assess ruffed grouse populations and for designing auditory surveys for this important game bird. 相似文献
The Rayleigh ratios RH have been measured for the depolarized scattering dilute solutions of N-ethylacetamide (EA), N-methylpropionamide (MP), and N-acetyl-pyrrolidine (AP) in P-dioxane, and dilute aqueous solutions of N-methylacetamide (MA), N,N-dimethylacetamide (DMA), EA, and MP. Squares of the optical anisot-ropies γ of the amides are obtained through extrapolation of these mesurements to infinite dilution. Values of γ2 found for EA and MP in dioxane are in good agreement with calculations based principally on the previously evaluated polarizability tensor of the amide group in conjunction with C? C and C? H bond polarizabilities. The calculations also involve averaging over all conformations, each being weighted according to the estimated conformational energy. The mean-squared optical anisotropies (γ2) of the oligoglycines and oligoalanines are calculated by similarly averaging over all skeletal conformations. The anistropic polarizability tensor \documentclass{article}\pagestyle{empty}\begin{document}$ \hat \alpha $\end{document} for the prolyl structural unit is derived for γ2 for AP. The much larger optical anisotropies exhibited by the amides when dissolved in water as compared with those observed in dixane are discussed. 相似文献
The kinetics and dose-dependence of activation of human neutrophils exposed to sequential additions of the chemotactic peptide n-formyl-methionyl-leucyl-phenylalanine (fMLP) have been investigated by multiwell microplate assays. Treatment of neutrophils with medium–high doses (from 10?8 to 5 × 10?7 M) of fMLP caused activation of superoxide anion (O) production, but prevented further activation by a subsequent addition of an optimal dose (from 10?7 M to 5 × 10?7 M) of fMLP. These findings represent an example of cell desensitization, or adaptation. However, neutrophils treated with low, sub-stimulatory doses (from 10?10 to 5 × 10?9 M) of the peptide and then treated with optimal doses of fMLP exhibited an O production that was two to three-fold higher than that induced by the same optimal doses on untreated cells. A similar phenomenon of homologous priming of the oxidative metabolism of neutrophil has not previously been described or characterized. Priming was maximal after about 30 min of incubation with fMLP, which differed from desensitization, which required only a few minutes. Homologous priming was not confined to O production, but was also observed with the release of the granule enzyme, lysozyme. Low doses of fMLP were also capable of triggering an increase of intracellular free Ca2+ and of fMLP membrane receptors, which are possible mechanisms responsible for priming. 相似文献
Oxygen uptake () and critical oxygen tension (Pcrit) were measured in resting perch Perca fluviatilis that were either fasting or digesting. Digestion caused to double (from 61 to 117 mg O2 kg?1h?1) and was associated with a rise in Pcrit (from 3·4 to 4·9 kPa), showing that the animal's digestive state must be considered when assessing the effect of hypoxia in natural conditions, and when defining optimal oxygen conditions in aquaculture. 相似文献
Solution conformations of the cyclic pentapeptide plant-hormone malformin A, whose conformational freedom is constrained by an intramolecular disulfide bridge, are derived and presented here. The nmr and CD data of Ptak are used to place restrictions on the search for possible malformin A solution conformers of low energy. Only two distinct conformers were found to be consistent with Ptak's data. Both structures are characterized by an internally buried (solvent-shielded) D -Cys2 amide proton, a seven-membered (1–3)hydrogen bond between (N–H) and (O?C), and a disulfide bridge conformation with a P chirality as manifested in the nmr study by the temperature independence of the amide proton chemical shifts for the D -Cys2 and D -Leu4 residues and the negative sign of the long wavelength maximum in the CD spectrum, respectively. Inspection of space-filling molecular models of both structures indicates severe steric barriers to their rapid interconversion. Thus, it appears that only one of the two conformers may be present in solution. The difference in their calculated dipole moments (4.6 and 6.9D) suggests an experimental method for distinguishing between the two proposed solution structures. 相似文献
A continuous stirred tank fermentor (CSTF) used for cultivation of the fungus Morchella crassipes in ammonia base waste sulfite liquor (NH3-WSL) was considered as a multivariable linear system around its operating point. Pulse testing on the inputs (inlet jacket temperature, inlet pH, inlet substrate concentration) and their responses at the outputs (biomass, outlet temperature, outlet jacket temperature, outlet pH, outlet substrate concentration) were used for numerical determination of the transfer function matrix: 相似文献
An attempt is made to give a thermodynamic interpretation of the complete temperature profile curve of ethanol formation. Taking into consideration an enhancing competition between thermal activation and thermal deactivation of ethanol formation at increasing temperatures and supposing that the ethanol production is affected by a reversible and an irreversible term of thermal deactivation of a modified ARRHENIUS equation being current for the total biokinetic sphere may be derived: . The quantities ΔH and ΔHD2T are identical with the temperature functions of the change of entropy caused by reversible and irreversible deactivation of ethanol formation, respectively. Accordingly for the yeast strain Saccharomyces cerevisiae Sc 5 the calculated entropy coefficients of reversible and irreversible thermal deactivation of ethanol formation amount to C = (0.245± 0.013) kJ/mol · deg.2 and C = (1.657 ± 0.046) kJ/mol · deg.2. 相似文献
The variation in the helix-coil transition temperature, TmN, with oligomer length, N, for the system ((I)) has been examined. The results for N = 4-13, measured in 0.2M Na+, have been analyzed in terms of the expression of Blake (1972): ((II)) where cm is the free oligomer concentration at TmN, and Vrf is the thermodynamic free volume available to a helical base-triplet residue. The correlation coefficient for the fit to expression (II) of data obtained over a 50° temperature range is 0.997 when ΔHr = ?12.6 kcal/mole of base-triplets (independent of oligomer length (N ? 4) or temperature), the value previously obtained from both calorimetry of (A)∞·2(U)∞ and (A)4 concentration dependence of Tm. It is found that Vrf = 8.0 × 10?4 1/mole (± 30%) or 1.33 Å3 per helical base-triplet, and is constant with temperature. A maximum value for Vrf of 21.0 × 10?4 1/M (± 1.3%), equivalent to 3.54 Å3 per helical basetriplet is obtained by the same treatment of the helix-coil transition data for the three-stranded helix formed by adenosine (N = 1) and 2(U)∞ obtained by Davies and Davidson (1971). 相似文献
The model used in this paper is Y = Xβ, where with unknown x0. Estimators of x0 are derived by putting βmx0 =βm+1 regarding βm+1 as a new unknown parameter. Formally we use the model Y = X1β+ + e where β′+ = (β0, …βm+1 and Then βm+1/ βm is a point estimator of x0. Assuming normality for e and taking the random variable z=βmx0?βm+1 we get a t-distributed variable and finally a confidence estimator of x0. The formulas are applied in dose response relations in antibiotic assays refering to a standard. Now we can take into account not only the dependence on the dose/concentration but also on the position on the test agar plate where the test solution is filled in. As a consequence the confidence interval of the unknown dose/concentration x0 becomes shorter and by it the statements more precise. 相似文献