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111.
Ivy Liu 《Biometrical journal. Biometrische Zeitschrift》2003,45(6):730-750
For an r × ctable with ordinal responses, odds ratios are commonly used to describe the relationship between the row and column variables. This article shows two types of ordinal odds ratios where local‐global odds ratios are used to compare several groups on a c‐category ordinal response and a global odds ratio is used to measure the global association between a pair of ordinal responses. When there is a stratification factor, we consider Mantel‐Haenszel (MH) type estimators of these odds ratios to summarize the association from several strata. Like the ordinary MH estimator of the common odds ratio for several 2 × 2 contingency tables, the estimators are used when the association is not expected to vary drastically among the strata. Also, the estimators are consistent under the ordinary asymptotic framework in which the number of strata is fixed and also under sparse asymptotics in which the number of strata grows with the sample size. Compared to the maximum likelihood estimators, simulations find that the MH type estimators perform better especially when each stratum has few observations. This article provides variances and covariances formulae for the local‐global odds ratios estimators and applies the bootstrap method to obtain a standard error for the global odds ratio estimator. At the end, we discuss possible ways of testing the homogeneity assumption. 相似文献
112.
Pavel Veprek Jan Jezek Jirí Velek Hatem Tallima Mona Montash Rashika El Ridi 《Journal of peptide science》2004,10(6):350-362
Four monoepitopic MAPs (MAP A, B, C and E) and one bis-diepitopic MAP B-E derived fromthe primary sequence of Schistosoma mansoni glyceraldehyde 3-phosphate dehydrogenase, previously tested in BALB/c mice, were examined for their immunogenicity and protective capacity in C57BL/6 mice. Despite multimerization into MAPs, MAP Aand MAP C were poorly immunogenic. In contrast toBALB/c mice, MAP E was non-immunogenic in C57BL/6 mice. Peptide B in the form of MAP B orbis-diepitopic MAPB-E elicited immune responses in C57BL/6 mice that were associated with a significant decrease in worm burden. The MAPs were prepared by the stepwise solid-phase peptide synthesis using Boc/Bzl chemistry, successfully purified on the RP-HPLC column and characterized by RP-HPLC, HPCE and MALDI-TOF MS techniques. A general strategy for MAPs purification is discussed here and the purification of MAP Band MAP E is documented in detail. 相似文献
113.
When agricultural land is no longer used for cultivation and allowed to revert to natural vegetation or replanted to perennial vegetation, soil organic carbon can accumulate. This accumulation process essentially reverses some of the effects responsible for soil organic carbon losses from when the land was converted from perennial vegetation. We discuss the essential elements of what is known about soil organic matter dynamics that may result in enhanced soil carbon sequestration with changes in land‐use and soil management. We review literature that reports changes in soil organic carbon after changes in land‐use that favour carbon accumulation. This data summary provides a guide to approximate rates of SOC sequestration that are possible with management, and indicates the relative importance of some factors that influence the rates of organic carbon sequestration in soil. There is a large variation in the length of time for and the rate at which carbon may accumulate in soil, related to the productivity of the recovering vegetation, physical and biological conditions in the soil, and the past history of soil organic carbon inputs and physical disturbance. Maximum rates of C accumulation during the early aggrading stage of perennial vegetation growth, while substantial, are usually much less than 100 g C m?2 y?1. Average rates of accumulation are similar for forest or grassland establishment: 33.8 g C m?2 y?1 and 33.2 g C m?2 y?1, respectively. These observed rates of soil organic C accumulation, when combined with the small amount of land area involved, are insufficient to account for a significant fraction of the missing C in the global carbon cycle as accumulating in the soils of formerly agricultural land. 相似文献
114.
The metabolic consequences of two defects in pyruvate metabolism of the hyphal fungus Aspergillus nidulans have been investigated by natural abundance 13C-NMR spectroscopy. A pyruvate dehydrogenase complex (pdh) mutant, grown on acetate, accumulates alanine upon starvation which is derived from mannitol reserves. The
-alanine level increases further upon incubation with the non-permissive substrate
-glucose.
-Glutamate is absent from these spectra as it is required both for the transamination of pyruvate and as a reaction on an impaired energy metabolism in such a pdh-deficient strain. A pyruvate carboxylase (pyc) mutant, grown upon acetate, only starts to accumulate alanine after a long incubation period with
-glucose, due to the long-lasting presence of phosphoenolpyruvate carboxykinase and malic enzyme, which are both induced by growth on acetate. When this strain is grown on
-fructose and
-glutamate, alanine also accumulates within 3 h upon transfer to
-glucose. 相似文献
115.
A. De Marco A. M. Petros R. A. Laursen M. Llinás 《European biophysics journal : EBJ》1987,14(6):359-368
The interaction of the isolated human plasminogen kringle 4 with the four -amino acid ligands -aminocaproic acid (ACA), N-acetyl-l-lysine (AcLys), trans-aminomethyl(cyclohexane)carboxylic acid (AMCHA) and p-benzylaminesulfonic acid (BASA) has been further characterized by 1H-NMR spectroscopy at 300 and 600 MHz. Pronounced high-field shifts, reaching 3 ppm, are observed for AMCHA resonances upon binding to kringle 4, which underscores the relevance of ligand lipophilic interactions with aromatic side chains at the binding site. Ligand titration curves for the nine His and Trp singlets found in the kringle 4 aromatic spectrum reveal a striking uniformity in the kringle response to the various ligands. The average binding curves exhibit a clear Langmuir absorption isotherm saturation profile and the data were analyzed under the assumption of one (high affinity) binding site per kringle. Equilibrium association constants (K
a
) and first order dissociation rate constants (k
off) were derived from linearized expressions of the Langmuir isotherm and of the spectral line-shapes, respectively. The results for the four ligands, at 295 K, pH* 7.2, indicate that: (a) AMCHA exhibits the strongest binding (K
a
=159 mM
-1) and ACA the weakest (K
a
=21 mM
–1) with AcLys and BASA falling in between; (b) ACA dissociates readily (k
off = 5.3 × 103 s–1) and AMCHA associates the fastest (k
off = 2.0 × 108
M
–1 s–1) while the kinetics for BASA exchange is relatively slow (k
off = 0.8 × 103 s–1, k
on = 0.6 × 108
M
–1s–1); (c) the ligand-binding kinetics is close to diffussion-controlled.Abbreviations ACA
-aminocaproic acid
- AcLys
N-acetyl-l-lysine
- AMCHA
t-aminomethyl(cyclohexane)carboxylic acid
- BASA
p-benzylaminesulfonic acid
- K4
kringle 4
- NOE
nuclear Overhauser effect
- ppm
parts-per-million
- pH*
glass electrode pH reading uncorrected for deuterium isotope effects
-
K
a
ligand-kringle 4 equilibrium association constant
-
k
off
ligand-kringle 4 dissociation rate constant
-
k
on
ligand-kringle 4 association rate constant 相似文献
116.
B. C. Loughman 《Plant and Soil》1987,99(1):63-74
Summary Little is known about the biochemical basis of the genotypic differences in the capacity for ion absorption and transport
shown by many crop species. If these differences reflect the abundance of a specific membrane component or the activity of
an enzyme we need to have some indication of thein vivo operation of these systems in whole plants. Thein vivo assessment of glycolytic enzymes is illustrated by the effects of mannose on the transport of phosphate in maize varieties.
The application of high resolution31P-NMR to the study of intermediary metabolismin vivo is also helpful in following transport capacity.
The five-fold rise in respiratory rate that occurs when freshly cut potato slices are maintained in aerated water for 24 hours
is accompained by the turning on of a wide range of biochemical systems. Major increases in the capacity for absorption of
phosphate from low concentrations (0.1 μM–10 μM) and in the phosphorylative ability of the tissue are seen, indicating the synthesis of a carrier involved in phosphate transport.
These capacities differ markedly between individual tissues of the tuber,i. e. pith, parenchyma, cortex and buds and large differences have been observed between comparable tissue from different varieties.
Varieties grown under similar conditions have been compared and shown to exhibit different kinetics with respect to the development
of the low concentration absorption site and in their sensitivity to the effects of uncouplers such as 2,4-dinitrophenol. 相似文献
117.
A reagent (I, N4-(9-fluorenylmethyloxycarbonyl-4-amino-1-oxyl-4-succinimidyloxycarbonyl-2,2,6,6-tetramethylpiperidine)) that acylates calmodulin specifically at lysines 75 and 148 was recently described (Jackson and Puett, 1984). Chromatographic procedures are described that permit purification to apparent homogeneity of a 1 : 1 and a 2 : 1 adduct characterized by modification at just Lys 75 or at Lys 75 and Lys 148, respectively. These adducts are suitable for detailed characterization in an effort to provide information on calmodulin structure-function relationships. The adducts were incapable of, or exhibited low potency (e.g., 0.1% that of calmodulin) in, stimulating the activity of an activatable bovine brain cyclic nucleotide phosphodiesterase (3,5-cyclic AMP 5-nucleotidehydrolase, EC 3.1.4.17) preparation. Electron paramagnetic resonance (EPR) spectroscopy of the adducts yielded rotational correlation times of approximately 3–6 nsec, in agreement with the expected value for a hydrated protein of this molecular weight (5–7 nsec). Thus, the nitroxide reporter group appears to monitor closely the motion of the protein, and there is no evidence of a major conformational change in the derivative relative to calmodulin. Interestingly, removal of the fluorenylmethyloxycarbonyl portion from the 1 : 1 adduct to give a deprotected 1 : 1 adduct resulted in apparent greater mobility of the probe, since the rotational correlation coefficient was found to be 1 nsec. Circular dichroic spectra were obtained over the wavelength interval 200–250 nm on the two adducts and on the deprotected 1 : 1 adduct. These derivatives, like calmodulin, exhibited a Ca2+-mediated increase in helicity, and the spectra of the adducts in the presence of a chelating agent and in the presence of saturating Ca2+ were similar to those obtained for calmodulin. Thus, the adducts have secondary structures similar to the native protein. Proton nuclear magnetic resonance spectra were determined in the aromatic region (6–8 ppm) for the deprotected 1 : 1 adduct before and after reduction of the nitroxide with ascorbate. The nitroxide had little effect on the chemical shifts of the two tyrosines and the single histidine relative to calmodulin, although the histidine C4 resonance was markedly altered by the addition of ascorbate. In order to explore in greater detail the tertiary structure of the 1 : 1 adduct, a reagent similar to I, but not paramagnetic, was synthesized. This compound II, -N-(9-fluorenylmethyloxycarbonyl)alanine N-hydroxysuccinimide ester, like I, forms a 1 : 1 adduct at Lys 75 and a 2 : 1 adduct at Lys 75 and Lys 148. Proton NMR spectra of adducts with II were not complicated by the relaxation effects arising from adducts with I; thus more definitive assignments could be made to the upfield resonances, including the fluorene protons. Again, it was possible to conclude that adduct formation had no major effect on the tertiary structure of the protein as monitored by chemical shifts associated with various residues. We conclude that modification of just Lys 75, a residue in the long connecting helix of calmodulin, does not lead to major changes in protein conformation but does interfere with the ability of calmodulin to stimulate an activatable form of bovine brain cyclic nucleotide phosphodiesterase. 相似文献
118.
J. Sianoudis A. C. Küsel A. Mayer L. H. Grimme D. Leibfritz 《Archives of microbiology》1987,147(1):25-29
P-31 NMR investigations were performed with the green alga Chlorella fusca under anaerobic conditions in the dark and in the light.In spectra of cells in the dark the signal of intracellular, nonvacuolar Pi indicates a pH in its chemical environment of 7.0–7.2. Upon illumination this signal looses intensity and shifts to lower field, corresponding to a pH of 7.7. Further downfield no other signal that could be attributed to a Pi-pool in more alkaline environment was detected. By the use of 2-deoxyglucose-6-phosphate as an indicator of cytoplasmic pH, this Pi-signal was assigned to the cytoplasm. The pH increase in the cytoplasm upon transfer of cells from the dark to the light is the same as that previously observed upon transfer of cells from anaerobic to aerobic conditions.In cells performing only cyclic photophosphorylation the cytoplasmic pH is lower than in photosynthesizing cells but still 0.2 pH units higher than in the cells in the dark. The reasons for the missing of a signal of stromal Pi and for the difference in cytoplasmic pH in photosynthesizing cells and those capable only of cyclic photophosphorylation are discussed.Non-standard abbreviations 2dG
2-Deoxyglucose
- dG-6-P
2-deoxyglucose-6-phosphate
- DCMU
3,4-dichlorophenyl-dimethylurea
- MOPSO
3-(N-morpholino)-2-hydroxypropane sulfonic acid
- P-31 NMR
P-31 nuclear magnetic resonance 相似文献
119.
Norma J. Greenfield Mussadeq Hussain John Lenard 《Biochimica et Biophysica Acta (BBA)/General Subjects》1987,926(3)
The vacuoles of logarithmic and stationary stage cells were compared by 31P-NMR with regard to pH, orthophosphate (Pi) content and average size of polyphosphate. The vacuoles of stationary cells had lower pH higher Pi content, and polyphosphates of longer average chain lenght, although total polyphosphate content was about the same as in logarithmic cells. The lower vacuolar pH in stationary cells was the major cause of a larger cytoplasmic-vacuolar pH gradient. Addition of NH4Cl, (NH4)2SO4, methylamine or amantadine at pH 8 to cells in either stage caused an icnrease in both cytoplasmic and vacuolar pH, with little or no change in the cytoplasmic-vacuolar pH gradient. However, the administration of ammonium salts to the cells at pH 8.0 resulted in rapid hydrolysis of the intravacuolar polyphosphate to tripolyphosphate and Pi, with attendant redistribution of Pi between the vacuolar and cytoplasmic compartments. 相似文献
120.
The internal pH of peroxisomes in the yeasts Hansenula polymorpha, Candida utilis and Trichosporon cutaneum X4 was estimated by 31P nuclear magnetic resonance (NMR) spectroscopy. 31P NMR spectra of suspensions of intact cells of these yeasts, grown under conditions of extensive peroxisomal proliferation, displayed two prominent Pi-peaks at different chemical shift positions. In control cells grown on glucose, which contain very few peroxisomes, only a single peak was observed. This latter peak, which was detected under all growth conditions, was assigned to cytosolic Pi at pH 7.1. The additional peak present in spectra of peroxisome-containing cells, reflected Pi at a considerably lower pH of approximately 5.8–6.0. Experiments with the protonophore carbonyl cyanide m-chlorophenylhydrazon (CCCP) and the ionophores valinomycin and nigericin revealed that separation of the two Pi-peaks was caused by a pH-gradient across a membrane separating the two pools. Experiments with chloroquine confirmed the acidic nature of one of these pools. In a number of transfer experiments with the yeast H. polymorpha it was shown that the relative intensity of the Pi-signal at the low pH-position was correlated to the peroxisomal volume fraction. These results strongly suggest that this peak has to be assigned to Pi in peroxisomes, which therefore are acidic in nature. The presence of peroxisome-associated Pi was confirmed cytochemically.Abbreviations CCCP
Carbonyl cyanide m-chlorophenylhydrazon
- DCCD
N,N-dicyclohexylcarbodiimide 相似文献