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1.
Consider the model Y ijk=μ + a i + b ij + e ijk (i=1, 2,…, t; j=1,2,…, B i; k=1,2…,n ij), where μ is a constant and a 1,b ij and eijk are distributed independently and normally with zero means and variances σ 2ad ij and σ 2, respectively, where it is assumed that the di's and dij's are known. In this paper procedures for estimating the variance components (σ 2, σ 2a and σ 2b) and for testing the hypothesis σ 2b = 0 and σ 2a = 0 are presented. In the last section the mixed model y ijk, where x ijkkm are known constants and β m's are unknown fixed effects ( m = 1, 2,…, p), is transformed to a fixed effect model with equal variances so that least squares theory can be used to draw inferences about the β m's. 相似文献
2.
To obtain general rules of peptide design using α,β-dehydro-residues, a sequence with two consecutive ΔPhe-residues, Boc-L -Val-ΔPhe–ΔPhe- L -Ala-OCH 3, was synthesized by azlactone method in solution phase. The peptide was crystallized from its solution in an acetone/water mixture (70:30) in space group P6 1 with a= b=14.912(3) Å, c= 25.548(5) Å, V=4912.0(6) Å 3. The structure was determined by direct methods and refined by a full matrix least-squares procedure to an R value of 0.079 for 2891 observed [ I?3σ( I)] reflections. The backbone torsion angles ? 1=?54(1)°, ψ 1= 129(1)°, ω 1=?177(1)°, ? 2 =57(1)°, ψ 2=15(1)°, ω 2 =?170(1)°, ? 3=80(1)°, ψ 3 =7(2)°, ω 3=?177(1)°, ? 4 =?108(1)° and ψ T4=?34 (1)° suggest that the peptide adopts a folded conformation with two overlapping β-turns of types II and III′. These turns are stabilized by two intramolecular hydrogen bonds between the CO of the Boc group and the NH of ΔPhe 3 and the CO of Val 1 and the NH of Ala 4. The torsion angles of ΔPhe 2 and ΔPhe 3 side chains are similar and indicate that the two ΔPhe residues are essentially planar. The folded molecules form head-to- tail intermolecular hydrogen bonds giving rise to continuous helical columns which run parallel to the c-axis. This structure established the formation of two β-turns of types II and III′ respectively for sequences containing two consecutive ΔPhe residues at ( i+2) and ( i+3) positions with a branched β-carbon residue at one end of the tetrapeptide. 相似文献
4.
The 3 way nested ANOVA model yijk = μ + ai + Bij + γk + (αγ)ik + epsilonijk With α (treatment or group effects) and γ (time) both being fixed effects and B (the individual effects) random and nested within α, is introduced and explored. The problems associated with the usual approach are explained. The alternative model Is developed and a method of evaluation via the method of linear contrasts is recomended. The test statistic has the distribution of a convolution of F-distributions. Further, a method of investigating the assumptions of the model is offered and a further generalization using path spaces (of dim. K) is developed. Here again the appropriate test statistic has the distribution of a convolution of F-distributions. This combined with the method of linear contrasts offers an elegant solution to the BEHRENS-FISHER problem. yijk = fik + Bij + epsilonijk 相似文献
5.
Consider the mixed model where xijk's are known constants, β k are unknown parameters and ai, eij are random variables independently and normally distributed with zero means and variances σ di and σ 2 respectively, where it is assumed that the di's are known ( di >0). This paper presents procedures for estimating the variance components σ, σ 2, 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 β k's in the model. 相似文献
6.
We suggest a new technique for estimating the relative drawdown of CO2 concentration (c) in the intercellular air space (IAS) across hypostomatous leaves (expressed as the ratio cd/cb, where the indexes d and b denote the adaxial and abaxial edges, respectively, of IAS), based on the carbon isotope composition (δ13C) of leaf cuticular membranes (CMs), cuticular waxes (WXs) or epicuticular waxes (EWXs) isolated from opposite leaf sides. The relative drawdown in the intracellular liquid phase (i.e., the ratio cc/cbd, where cc and cbd stand for mean CO2 concentrations in chloroplasts and in the IAS), the fraction of intercellular resistance in the total mesophyll resistance (rIAS/rm), leaf thickness, and leaf mass per area (LMA) were also assessed. We show in a conceptual model that the upper (adaxial) side of a hypostomatous leaf should be enriched in 13C compared to the lower (abaxial) side. CM, WX, and/or EWX isolated from 40 hypostomatous C3 species were 13C depleted relative to bulk leaf tissue by 2.01–2.85‰. The difference in δ13C between the abaxial and adaxial leaf sides (δ13CAB ? 13CAD, Δb–d), ranged from ??2.22 to +?0.71‰ (??0.09 ± 0.54‰, mean ± SD) in CM and from ??7.95 to 0.89‰ (??1.17 ± 1.40‰) in WX. In contrast, two tested amphistomatous species showed no significant Δb–d difference in WX. Δb–d correlated negatively with LMA and leaf thickness of hypostomatous leaves, which indicates that the mesophyll air space imposes a non-negligible resistance to CO2 diffusion. δ13C of EWX and 30-C aldehyde in WX reveal a stronger CO2 drawdown than bulk WX or CM. Mean values of cd/cb and cc/cbd were 0.90 ± 0.12 and 0.66 ± 0.11, respectively, across 14 investigated species in which wax was isolated and analyzed. The diffusion resistance of IAS contributed 20 ± 14% to total mesophyll resistance and reflects species-specific and environmentally-induced differences in leaf functional anatomy. 相似文献
7.
The Δ 5-3-ketosteroid isomerase from Pseudomonas putida biotype B has been crystallized. The crystals belong to the space group P2 12 12 1 with unit cell dimensions of a = 36.48 Å, b = 74.30 Å, c = 96.02 Å, and contain one homodimer per asymmetric unit. Native diffraction data to 2.19 Å resolution have been obtained from one crystal at room temperature indicating that the crystals are quite suitable for structure determination by multiple isomorphous replacement. 相似文献
8.
Bacterial chemotaxis receptor modifying enzymes from Salmonella typhimurium have been crystallized using microseeding techniques. The crystals of the S-adenosyl-L -methionine-dependent methyl transferase, CheR, belong to the monoclinic space group P2 1 with cell constants a = 55.1 Å, b = 48.1 Å, c = 63.1 Å, β = 112.3°. The crystals of the catalytic domain of the methylesterase, CheB, belong to the trigonal space group P3 221 or P3 121 with unit cell dimensions of a = b = 63.4 Å, c = 86.8 Å. Both crystals contain one molecule per asymmetric unit and have calculated Matthews' volumes of 2.4 Å 3/Da. © 1995 Wiley-Liss, Inc. 相似文献
9.
A series of new monophosphates of 1-[2-(phosphonomethoxy)alkyl]thymines, such as PMPTp , 3-MeO-PMPTp, HPMPTp, and FPMPTp, were synthesized and tested for their ability to inhibit human thymidine phosphorylase. Kinetic measurements of enzyme activity were performed using thymidine and inorganic phosphate as the substrates. The data show that some monophosphates provide a considerable increase of the multisubstrate inhibitory effect. The highest inhibitory potency was found with ( R)-FPMPTp 4c ( K i dT = 4.09 ± 0.47 μM, K i(P i) = 2.13 ± 0.29 μM) and ( R) 3-MeO-PMPTp 4d ( K i dT = 5.78 ± 0.71 μM, K i(P i) = 2.71 ± 0.37 μM). 相似文献
10.
Trypanosoma brucei ornithine decarboxylase, expressed and purified from E. coli, has been crystallized by the vapor diffusion method using PEG 3350 as a precipitant. The crystals belong to the monoclinic space group P2 1 and have cell constants of a = 66.3 Å, b = 151.8 Å, c = 83.7 Å, and β = 101.2°. While larger crystals are twinned, smaller crystals (0.4 × 0.3 × 0.05 mm 3) are single. 相似文献
11.
Diaziridines are very interesting representatives of organic compounds containing stereogenic nitrogen atoms. In particular, 1,2-dialkyldiaziridines show extraordinarily high stereointegrity. The lone electron pairs of the nitrogen atoms are in trans configuration, avoiding a four-electron repulsive interaction. Furthermore, the trans configuration of the substituents at the nitrogen atoms is energetically favored because of reduced steric interactions. Therefore only two stereoisomers (enantiomers) are observed. At elevated temperatures the enantiomers are interconverting because of the limited stereointegrity of the chirotopic nitrogen atoms. The enantiomerization rate constants and the activation parameters of interconversion are of great interest. Here, we investigated the stereodynamics of a set of small 1,2-dialkyldiaziridines bearing short substituents (Me, Et, iPr, tBu), using enantioselective dynamic gas chromatography (DGC). Separation of enantiomers of all compounds, including the highly volatile 1,2-dimethyldiaziridine, was achieved using heptakis(2,3-di- O-ethyl-6- O-tert-butyldimethylsilyl)-β-cyclodextrin in 50% PS086 (w/w) as chiral stationary phase in fused silica capillaries with a length of up to 50 m. Measurements at variable temperatures were performed and reaction rate constants were determined using the unified equation of chromatography implemented in the software DCXplorer. The activation barriers at room temperature for 1-( tert-butyl)-2-ethyldiaziridine, Δ G╪298K = 123.8 kJ mol –1 (Δ H╪ = 115.5 ± 2.9 kJ mol –1, Δ S╪ = –28 ± 1 J mol –1 K –1), and 1-ethyl-2-isopropyldiaziridine, Δ G╪298K = 124.2 kJ mol –1 (Δ H╪ = 113.1 ± 2.4 kJ mol –1, Δ S╪ = –37 ± 2 J mol –1 K –1), were determined, representing some of the highest values observed for nitrogen inversion in diaziridines. Chirality 00:000–000, 2013. © 2013 Wiley Periodicals, Inc. 相似文献
12.
The spread of bean rust from three types of inoculum sources (area, line, and point) was studied under field conditions in two seasons. Disease intensity ( y) over time was quantified as incidence of diseased plants, incidence of diseased leaves, and disease severity at distances ( d) of 0.3, 0.7, 1.5, 2.7, 4.3, 6.5, and 8.7 m from the inoculum sources. Seven curvilinear models were compared and the models that best explained the gradients of bean rust were y = ad?b exp( cd), y = a exp(– bdc) and y = a exp(– bd); where a was proportion of disease near the source, d was distance in metres, b was the slope, and c was a shape parameter. For general analysis to compare the slopes of the gradients, the gradient curves were linearized by ln( y) versus d and the parameters ln( a) (intercept) and b (slope) were estimated. The three measures of disease intensity and the three types of inoculum sources had estimated gradient parameters that were statistically different. The incidence of diseased plants rapidly approached y = 1.0 and the gradient slopes were near zero. Also with the ln( y) linearization, the gradients of the incidence of diseased leaves had slopes flatter than the gradients of disease severity. The gradient slopes from area sources of inoculum were flatter than from line sources, which in turn were flatter than from point sources. Late in the epidemics, the b-values became similar for all combinations of inoculum sources × assessment types. The interpretation of flattening of the gradients was confounded because aberrations in transformations occurred with most models. That is, when the intensity of disease (incidence or severity) approached the maximum, the increases in the intercepts were restricted and this restriction was responsible for most of the flattening. No flattening of gradients occurred over time when the gompit gradient model [–ln(–ln( y/ ymax)) = –ln(–ln( a))? b ln( d)] was used for these same disease values. The fitting of models to the gradients served little purpose except to classify the curves in a general way. A new statistic, the area under the disease gradient curve (AUDGC), is proposed to compare epidemics. 相似文献
13.
Values for the thermodynamic quantities, Δ H° = 11.8 ± 2.0 Kcal/mole and Δ S° = 43.6 ± 6.0 e.u., of the 3-13 helix–coil equilibrium of isolated S-peptide (19 residue N-terminal fragment of ribonuclease A) in aqueous solution (3 m M, 1 M NaCl, pD 5.4) have been determined from a joint analysis of the Thr 3γ, Ala 6β, Phe 8 meta, and Phe 8 para 1H chemical shift vs temperature curves (?7 to 80°C) in several aqueous–trifluorethanol mixtures. Chemical shifts in the coil and in the helix have been determined for up to 16 protons belonging to the 3-13 fragment. Thermodynamic parameters have also been determined for C-peptide (13 residue fragment) and a number of S-peptide derivatives. From the variation of the values of the thermodynamic parameters at p D 2.5, 5.4, and 8.0, a quantitation of the two helix-stabilizing side-chain interactions can be made: (1) Δ(Δ H°) ? 5 Kcal/mole and Δ(Δ S°) ? 18 e.u. for the salt bridge Glu 2 ? … Arg 10 + and (2) Δ(Δ H°) ? 3 Kcal/mole and Δ(Δ S°) = 9 e.u. for the one in which the His 12 + imidazolium group is involved, presumably a partial stacking with the Phe 8 side chain. 相似文献
14.
α, β-Dehydroamino acids are expected to provide conformational constraint to the peptide backbone. A pentapeptide containing two dehydrophenylalanines (Δ ZPhe) separated by one L -amino acid has been synthesized and its solid state conformation determined. The pentapeptide, Boc-Gly-Δ ZPhe-Leu-Δ ZPhe-Ala-NHCH 3, crystallizes from aqueous methanol in the orthorhombic space group P2 12 12 1. There are four formula units, C 35H 46N 6O 7, in a unit cell of dimensions a = 10.155(3), b = 15.175(1), and c = 23.447(2) Å, at room temperature. The structure was solved by direct methods program, SIR88, and refined to a final R = 0.038 based on 3049 reflections with I > 2σ( I). All the peptide links are trans and the backbone conformation of the pentapeptide can be described as a 3 10-helix, with mean ?, ψ values of ?65.1° and ?22.8° (the value is averaged over the first four residues). There are four intramolecular 4 → 1 type hydrogen bonds characteristic of 3 10-type helices. In the crystal, the helices are held together by intermolecular N? H…?O?C head-to-tail and lateral hydrogen bonding between symmetry related molecules. This mode of packing is similar to the packing motifs observed so often in other oligopeptides that adopt a 3 10-helical structure. © 1993 John Wiley & Sons, Inc. 相似文献
15.
The crystal structures of Bu tCO-L -Pro-L -Pro-NHMe, H 2O ( 1: monoclinic; P2 1; a = 6.662, b = 11.067, c = 12.205 Å; β = 96.28°) and Bu tCO-L -Pro-D -Pro-NHMe ( 2: monoclinic; P2 1; a = 10.770, b = 15.039, c = 11.325 Å; β = 110.00°) have been solved by x-ray diffraction. Structure 1 accommodates an open disposition with intermolecular interactions involving the water molecule, while 2 is βII-folded by an intramolecular i + 3 → i hydrogen bond. In both derivatives, small thermal parameters are indicative of fairly fixed conformations for the proline rings. Comparison between conformations of either isolated or adjacent L -Pro residues in the crystal structures of unstrained oligopeptides shows that the conformational properties of L -Pro-L -Pro sequences are probably a simple combination of those found for isolated L -Pro residues. 相似文献
16.
The dehydro-residue containing peptides N-Ac-dehydro-Phe-L -Leu-OCH 3 ( I ) and N-Ac-dehydro-Phe-NorVal-OCH 3 ( II ) were synthesized by the usual workup procedures. The peptides crystallize from their solutions in methanol in space group P6 5: ( I ) a = b = 12.528(2) Å, c = 21.653(5) Å; ( II ) a = b = 12.532(2) Å, c = 21.695(4) Å. The structures were determined by direct methods. Both peptides adopt similar conformations with ?,ψ of dehydro-Phe as follows: ( I ) ?57.0(5)° and ?37.0(5)°; ( II ) ?56.0(5),° and ?37.5(5)°. The observed data on dehydro-Phe when placed at the ( i + 1) position show that the ?,ψ values of dehydro-Phe are either ?60°, 140° or ?60°, ?30°. The conformation of ?60°, 140° can be accommodated only with a flexible residue at the ( i + 2) position while the ?,ψ values of ?60°, ?30° are obtained with a bulky residue at the ( i + 2) position as in the present structures. The molecules are packed in a helical way along the c axis. These are held by two strong intermolecular hydrogen bonds involving both NH as donors and acetyl group and dehydro-Phe oxygen atoms as acceptors. © 1994 John Wiley & Sons, Inc. 相似文献
17.
Single crystals were grown from affinity-purified stinging nettle lectin and from its complex with the specific trisaccharide NN′ N″ -triacetylchitotriose by vapor diffusion at room temperature. The lectin crystallizes in space group P2 12 12 1 with unit cell dimensions a = 54.3 (1) Å, b = 62.2 (1) Å, and c = 92.4 (2) Å, and diffracts to 3.0 Å resolution. The asymmetric unit contains three lectin monomers. The crystals of the lectin-trisaccharide complex have space group P2 12 12 1 with cell constants a = 37.69 (4) Å, b = 48.97 (6) Å, and c = 57.32 (4) Å. These crystals diffract to at least 2.0 Å resolution and the asymmetric unit contains one lectin monomer. A three-dimensional X-ray structure determination is on its way. © 1993 Wiley-Liss, Inc. 相似文献
18.
Consider the two linear regression models of Y ij on X ij, namely Y ij = β io + β il X ij + ε ij, j = 1,2,…, ni, i = 1,2, where ε ij are assumed to be normally distributed with zero mean and common unknown variance σ 2. The estimated value of a mean of Y 1 for a given value of X 1 is made to depend on a preliminary test of significance of the hypothesis β 11 = β 21. The bias and the mean square error of the estimator for the conditional mean of Y 1 are given. The relative efficiency of the estimator to the usual estimator is computed and is used to determine a proper choice of the significance level of the preliminary test. 相似文献
19.
X-ray diffraction studies have been carried out on a single crystal of the photosynthetic inhibitors N-(3,4-dichlorophenyl)-N′-dimethylurea (DCMU) and its newly synthesized spin-labeled analog N-(3,4-dichlorophenyl)-N′-(3,3,5,5-tetramethylpiperidine-4-oxyl)-urea (DTPU). The synthesis of DTPU as well as its crystallographic data are reported. The crystal system of both compounds is monoclinic with a space group P2 1/ c. The cell constants of DCMU are a = 7.759(1), b = 14.737(3), c = 9.233(2) Å, β = 100.99(6)°; of DTPU they are a = 6.976(1), b = 11.998(2), c = 23.585(3) Å, β = 91.38(5)°. Comparison of conformational parameters of DCMU and DTPU reveal differences in the dihedral angle between the aromatic ring and the ureido plane. The measured volumes of DCMU and DTPU are 259.1 and 493.3 Å 3, respectively. These figures suggest the size of the binding site of the inhibitors in the photosynthetic membrane. 相似文献
20.
Some theoretical studies have predicted that the conformational freedom of the α-aminoisobutyric acid (H-Aib-OH) residue is restricted to the α-helical region of the Ramachandran map. In order to obtain conformational experimental data, two model peptide derivatives, MeCO-Aib-NHMe 1 and Bu tCO-LPro-Aib-NHMe 2 , have been investigated. The Aib dipeptide 1 crystallizes in the monoclinic system ( a = 12.71 Å, b = 10.19 Å, c = 7.29 Å, β = 110.02°, Cc space group) and its crystal structure was elucidated by x-ray diffraction analysis. The azimuthal angles depicting the molecular conformation (? = ?55.5°, ψ = ?39.3°) fall in the α-helical region of the Ramachandran map and molecules are hydrogen-bonded in a three-dimensional network. In CCl 4 solution, ir spectroscopy provides evidence for the occurrence of the so-called 5 and C 7 conformers stabilized by the intramolecular i → i and i + 2 → i hydrogen bonds, respectively. The tripeptide 2 was studied in various solvents [CCl 4, CD 2Cl 2, CDCl 3, (CD 3) 2SO, and D 2O] by ir and pmr spectroscopies. It was shown to accommodate predominantly the βII folded state stabilized by the i + 3 → i hydrogen bond. All these experimental findings indicate that the Aib residue displays the same conformational behavior as the other natural chiral amino acid residues. 相似文献
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