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1.
The salt-soluble proteins of groundnut meal were fractionated by precipitation with (NH 4) 2SO 4 by increasing the (NH 4) 2SO 4 saturation in steps of 10%. The sharp separation into arachin and conarachin claimed by earlier workers was not achieved, as protein was precipitated at each stage from 20 to 100% saturation with (NH 4) 2SO 4. The fractions so obtained were examined by disc electrophoresis on polyacrylamide gel and the amino acid compositions were determined by ion-exchange chromatography. Differences in both electrophoretic pattern and amino acid composition were found. The protein precipitated by CaCl 2 solution was similar in yield, nitrogen content, electrophoretic pattern, and amino acid composition to the fraction precipitating at 10–20% (NH 4) 2SO 4 saturation. The main differences in amino acid composition of the various fractions precipitated by (NH 4) 2SO 4 were found in the amino acids cystine, methionine, and lysine, which increased with increase in (NH 4) 2SO 4 saturation. The electrophoretic pattern and amino acid composition of “conarachin” varied according to the method of preparation. 相似文献
2.
Certain inorganic salts like KNO 3, KCl, K 2SO 4, Ca(NO 3) 2 and NH 4NO 3 extend longevity of cut carnation flowers. The effect of KNO 3 was studied in some detail. There is an osmotic adjustment in response to KNO 3 treatment. The osmotic concentration change occurred in the external as well as in the internal compartments. The osmotic concentration change in the external compartment is well correlated with extension of longevity. The effect of KNO 3 on the sensitivity to ethylene, and its significance in delaying senescence is discussed. 相似文献
3.
Using the pressure volume analysis (PV analysis) on the shoots of Norway spruce ( Picea abies [L.] Karst.) and the here presented capillary microcryoscopy of the needle press sap of the same shoots, it was possible to determine the amount of apoplastic water in the needles (W an) as well as in the defoliated shoots (W as). Additionally, the bulk osmotic pressure at full water saturation in the symplast of the needles and defoliated shoots (π on and π os) was determined. The dependence of the bulk-averaged turgor pressure (P t) on the water content and the relationship between the bulk modulus of elasticity of the needles (? n) and the bulk-averaged needle turgor pressure (P tn) was shown with help of the PV analysis on the whole shoots and defoliated shoots. The study was conducted at the end of the vegetation period in 1987 and during winter 1988. The proportion of W an in the total needle water content (W tn) was 14% in September 1987 and 12.5% in March 1988. The respective percentage of W as in W ts were 27% and 25%. The amount of apoplastic water depended on the ratio of the dry weight of defoliated shoots to the dry weight of the whole shoots. A standard mean value for the amount of W an in the total water content of the shoots (W t) was therefore not possible. The bulk osmotic pressure at full water saturation in the needle symplasts was –1.9 MPa in September 1987 and –2.2 MPa in winter 1988. The respective values of the bulk osmotic pressures in the symplast of the defoliated shoots (π os) were –1.5 MPa and –1.7 MPa. Thus π on was 0.1 MPa lower and π os 0.3–0.4 MPa higher than the average osmotic pressure during full water saturation in the symplast of the whole shoots (π o). The relation between bulk-averaged turgor pressure and water content showed that during water loss P tn dropped more rapidly than the turgor pressure of defoliated shoots (P ts). Consequently the needles were less elastic than the defoliated shoots. The turgor values of whole shoots followed an intemediate course between P tn and P ts. The flat course of P ts seems to be the main reason for the often observed “plateau” of ψ-isotherms of whole shoots near full turgor. 相似文献
4.
The respiration of potato tubers ( Solanum tuberosum var. Russet Burbank) which have been kept at room temperature for 10 days is stimulated upon subsequent treatment with C 2H 4 (10 microliters per liter) and O 2. The respiratory rise reaches a peak in 24 to 30 hours and thereafter declines. Coincident with the rise in tuber respiration is an increase in the respiratory rates of fresh slices and isolated mitochondria. Slices and mitochondria from C 2H 4- and O 2-treated tubers also display substantial resistance to CN, and the resistant respiration is inhibited by hydroxamates. The longer the tubers are stored after harvest, the less effective is C2H4 in causing CN resistance in slices and mitochondria from treated tubers. Addition of 10% CO2 to the C2H4-O2 mixture, however, causes extensive CN resistance to develop, even in slices and mitochondria from old tubers. The results show that C2H4, O2, and CO2 act synergistically to induce alternative path development in potatoes. 相似文献
5.
A model is proposed for the relationship between net photosynthetic rate (N) and light Intensity at a given concentration of CO 2 in the air ([CO 2] a). The model provides a prediction of the sum of the diffusion resistances (Σr), the capacity (K) of the leaf to fix CO 2, the concentration of CO 2 at the point of photosynthesis ([CO 2] g), and the respiration rate (R). The model fits the available data well and provides a frame work by which future research may be guided. The calculated values of [CO 2] g decreased from [CO 2] g at the compensation point to a nearly constant value at high tight intensities. [CO 2] g high light infensitit-s range from 32 to 144 μ/l (volume) depending on the species. When these values of [CO 2] g, are used in the diffusion equation, the resulting levels of the mesophyll resistance (r m) are lower than those calculated by using the assumptions that [CO 2] g equals zero. The plants which had (he higher photosynthetic rates at a given light intensity and [CO 2] a had grealer values of [CO 2] g than those with lower photo-synthetic rates. The calculated rates of respiration of wheat leaves were twice as high as those measured in the dark. This suggests that the light respiration rate may be twice as great as the dark respiration rate at the same temperature. The calculated values of K demonstrate variability within and between species. The maximum N was independent of K. A relationship between K and the maximum quantum efficiency, at constant levels of [CO 2] g, was demonstrated in several species. The Σr was inversely related to the maximum rate of photosynthesis for the species investigated. The values of r m calculated for cotton were inversely related to [CO 2] a suggesting that the transfer of [CO 2] in the cell may involve a concentration dependent chemical reaction in addition to or rather than a physical diffusion process. 相似文献
6.
Binaural hearing involves using information relating to the differences between the signals that arrive at the two ears, and it can make it easier to detect and recognize signals in a noisy environment. This phenomenon of binaural hearing is quantified in laboratory studies as the binaural masking-level difference (BMLD). Mandarin is one of the most commonly used languages, but there are no publication values of BMLD or BILD based on Mandarin tones. Therefore, this study investigated the BMLD and BILD of Mandarin tones. The BMLDs of Mandarin tone detection were measured based on the detection threshold differences for the four tones of the voiced vowels /i/ (i.e., /i1/, /i2/, /i3/, and /i4/) and /u/ (i.e., /u1/, /u2/, /u3/, and /u4/) in the presence of speech-spectrum noise when presented interaurally in phase (S 0N 0) and interaurally in antiphase (S πN 0). The BILDs of Mandarin tone recognition in speech-spectrum noise were determined as the differences in the target-to-masker ratio (TMR) required for 50% correct tone recognitions between the S 0N 0 and S πN 0 conditions. The detection thresholds for the four tones of /i/ and /u/ differed significantly ( p<0.001) between the S 0N 0 and S πN 0 conditions. The average detection thresholds of Mandarin tones were all lower in the S πN 0 condition than in the S 0N 0 condition, and the BMLDs ranged from 7.3 to 11.5 dB. The TMR for 50% correct Mandarin tone recognitions differed significantly ( p<0.001) between the S 0N 0 and S πN 0 conditions, at –13.4 and –18.0 dB, respectively, with a mean BILD of 4.6 dB. The study showed that the thresholds of Mandarin tone detection and recognition in the presence of speech-spectrum noise are improved when phase inversion is applied to the target speech. The average BILDs of Mandarin tones are smaller than the average BMLDs of Mandarin tones. 相似文献
7.
PMR investigations on the diastereomeric phosphate methyl protons of the dinucleoside ethyl phosphotriesters Tp(C 2H 5)T, dA, and dIp(C 2H 5)dI have been used to study the conformational changes of these dimersin solution. In D 2O (273°K), the diastereomeric phosphate-methly groups of Tp(C 2H 5)T appear as a triplet. The methyl resonances of dIp(C 2H 5)dI and dAp(C 2H 5)dA appear as two sets of triplets and their chemical shift differences (δ 1 ? δ 2), decrease with increasing temperature, finally becoming zero at 292°K and 333°K, respectively. The same phenomenon is observed for dAp(C 2H 5)dA in CD 3OD; in this detacking solvent, the difference (δ 1 ? δ 2) diminishes to zero at a lower temperature (261°K). At room temperature in D 2O, the chemical shift of the phosphate methyl of Tp(C 2H 5)T appears at lower field than those of dIp(C 2H 5)dI or dAp(C 2H 5)dA. The differences between the chemical shifts of these groups (δ I ? δ T or δ A ? δ T) increase with increasing temperature, and reach maximal values at 301°K and 333°K, respectively. The results suggest that at low temperature the largest fraction of the dimer population exists in a stacked state, with the phosphate-ethyl groups outside the stack. Increasing temperature causes an oscillation of the bases and a shift in the dimer population away from the stacked state. Finally at high temperature, the planar bases rorate with respect to one another and in the case of dIp(C 2H 5)dI and dAp(C 2H 5)dA, the ethyl groups experience shielding by the anisotropic ring current of the five-membered ring of the bases. Thus, the current pmr studies and those reported earlier from our laboratory support an “oscillation-rotation model” for the unstacking process of the dimers. The relationship of this model and the “two-state model” is discussed. 相似文献
8.
Endothelial dysfunction is associated with increase in oxidative stress and low NO bioavailability. The endothelial NO synthase (eNOS) uncoupling is considered an important factor in endothelial cell oxidative stress. Under increased oxidative stress, the eNOS cofactor tetrahydrobiopterin (BH 4) is oxidized to dihydrobiopterin, which competes with BH 4 for binding to eNOS, resulting in eNOS uncoupling and reduction in NO production. The importance of the ratio of BH 4 to oxidized biopterins versus absolute levels of total biopterin in determining the extent of eNOS uncoupling remains to be determined. We have developed a computational model to simulate the kinetics of the biochemical pathways of eNOS for both NO and O 2•− production to understand the roles of BH 4 availability and total biopterin (TBP) concentration in eNOS uncoupling. The downstream reactions of NO, O 2•−, ONOO −, O 2, CO 2, and BH 4 were also modeled. The model predicted that a lower [BH 4]/[TBP] ratio decreased NO production but increased O 2•− production from eNOS. The NO and O 2•− production rates were independent above 1.5 μM [TBP]. The results indicate that eNOS uncoupling is a result of a decrease in [BH 4]/[TBP] ratio, and a supplementation of BH 4 might be effective only when the [BH 4]/[TBP] ratio increases. The results from this study will help us understand the mechanism of endothelial dysfunction. 相似文献
9.
The effect of H 2O 2 on the primary structure of OxyHb was studied. Upon treatment of Oxy Hb with H 2O 2 ([Heme]/[H 2O 2] =I), tryptophan and methionine residues of the /-chain were modified. Treatment of ApoHb with H 2O 2 resulted in the modification of histidine and methionine residues in both globin chains. Tryptophan residues were unaffected. Modification of methionine residues in both the β-chain of OxyHb and ApoHb probably results from the direct oxidation of mcthionine by H 2O 2. The modification of histidine residues in ApoHb may be mediated by a metal-catalyzed oxidation system comprised of H 2O 2 and histidine-bound iron. The H 2O 2-mediated modification of tryptophan in the OxyHb β-chain. however, requires the heme moiety. 相似文献
10.
The kinetics of the addition reactions of tetracyanoethylene (TCNE) to trans-[Rh(RNC) 2(PR′ 3) 2]ClO 4, where R = p-CH 3OC 6H 4, p-ClC 6H 4, and C 6H 11 and R′ = C 6H 5 and C 6H 5O, in acetonitrile, acetone, and tetrahydrofuran (THF) have been investigated employing stopped-flow techniques. The reaction is first order with respect to both complex and TCNE. The reaction rate increases with increasing solvent polarity in the order of THF < acetone < acetonitrile. The activation parameters for the reactions of [RH(p-CH 3OC 6H 4NC) 2(PPh 3) 2]ClO 4 in the three solvents were: ΔH *, 7.6, 3.5, 2.2 kcal mol −1; ΔS *, −15.2, −27.7, −28. e.u. The nature of the transition state and ligand effects on the rate of reaction are discussed. 相似文献
11.
Submergence in water greatly stimulates internodal elongation in excised stem sections of deep-water rice ( Oryza sativa L. cv. Habiganj Aman II) and inhibits growth of leaf blades and leaf sheaths. The highest rates of internodal growth have been observed in continuous light. Very little growth occurs in submerged sections kept in darkness or incubated under N 2 in the light. The effect of submergence on the growth of deep-water rice is, at least in part, mediated by C 2H 4, which accumulates in the air spaces of submerged sections. This accumulation results from increased C 2H 4 synthesis in the internodes of submerged sections and reduced diffusion of C 2H 4 from the tissue into the water. Increased C 2H 4 levels accelerate internodal elongation and inhibit the growth of leaves. Compounds capable of changing the rate of C 2H 4 synthesis, namely aminoethoxyvinylglycine, an inhibitor of C 2H 4 synthesis, and 1-aminocyclopropane-1-carboxylic acid, the immediate, precursor of C 2H 4, have opposite effects on growth of internodes and leaves. The enhancement of internodal elongation by C 2H 4 is particularly pronounced in an atmosphere of high CO 2 and low O 2. The increase in C 2H 4 synthesis in internodes of submerged sections is primarily triggered by reduced atmospheric concentrations of O 2. The rate of C 2H 4 evolution by internodes isolated from stem sections and incubated in an atmosphere of low O 2 is up to four times greater than that of isolated internodes incubated in air. In contrast, C 2H 4 evolution from the leaves is reduced under hypoxic conditions. The effect of submergence on growth of stem sections of deep-water rice can be mimicked by exposing non-submerged sections to a gas mixture which is similar to the gaseous atmosphere in the internodal lacunae of submerged sections, namely 3% O 2, 6% CO 2, 91% N 2 (by vol.) and 1 l l -1 C 2H 4. Our results indicate that growth responses obtained with isolated rice stem sections are similar to those of intact deep-water rice plants.Abbreviations ACC
1-aminocyclopropane-1-carboxylic acid
- AVG
aminoethoxyvinylglycine 相似文献
12.
This study evaluated the ability of the microorganisms Rhizopus oryzae (CCT7560) and Trichoderma reesei (QM9414), producers of generally recognized as safe (GRAS) enzymes, to reduce the level of aflatoxins B 1, B 2, G 1, G 2, and M 1. The variables considered to the screening were the initial number of spores in the inoculum and the culture time. The culture was conducted in contaminated 4 % potato dextrose agar (PDA) medium, and the residual mycotoxins were determined every 24 h by HPLC-FL. The fungus R. oryzae has reduced aflatoxins B 1, B 2, and G 1 in the 96 h and aflatoxins M 1 and G 2 in the range of 120 h of culture by approximately 100 %. The fungus T. reesei has reduced aflatoxins B 1, B 2, and M 1 in the 96 h and aflatoxin G 1 in the range of 120 h of culture by approximately 100 %. The highest reduction occurred in the middle of R. oryzae culture. 相似文献
13.
The relationship between plasma levels of 15-keto-13, 14-dihydro-prostaglandin E 2 (15K-H 2-PGE 2) and serum calcium levels was studied in nontumor-bearing rabbits and in rabbits bearing the VX 2 carcinoma intramuscularly and intra-abdominally. The plasma levels of 15K-H 2-PGE 2 in the two groups of tumor-bearing animals did not vary significantly but was several fold greater than in nontumor-bearing rabbits. Rabbits bearing the VX 2 carcinoma intramuscularly developed hypercalcemia between the second and third week after implantation of neoplastic tissue and remained hypercalcemic until they expired. The serum calcium levels in rabbits bearing the VX 2 carcinoma intra-abdominally did not vary significantly from those of nontumor-bearing rabbits. The differences in the serum calcium levels in rabbits bearing the VX 2 carcinoma at intramuscular and intra-abdominal implant sites may be related to different extents of metabolism by the lung and by the liver of prostaglandin E 2 or other cyclooxygense products of polyenoic fatty acids produced by the tumor. 相似文献
14.
Nucleoside base modifications can alter the structures and dynamics of RNA molecules and are important in tRNAs for maintaining translational fidelity and efficiency. The unmodified anticodon stem–loop from Escherichia coli tRNA Phe forms a trinucleotide loop in solution, but Mg 2+ and dimethylallyl modification of A 37 N6 destabilize the loop-proximal base pairs and increase the mobility of the loop nucleotides. The anticodon arm has three additional modifications, ψ 32, ψ 39, and A 37 C2-thiomethyl. We have used NMR spectroscopy to investigate the structural and dynamical effects of ψ 32 on the anticodon stem-loop from E.coli tRNA Phe. The ψ 32 modification does not significantly alter the structure of the anticodon stem–loop relative to the unmodified parent molecule. The stem of the RNA molecule includes base pairs ψ 32-A 38 and U 33–A 37 and the base of ψ 32 stacks between U 33 and A 31. The glycosidic bond of ψ 32 is in the anti configuration and is paired with A 38 in a Watson–Crick geometry, unlike residue 32 in most crystal structures of tRNA. The ψ 32 modification increases the melting temperature of the stem by ~3.5°C, although the ψ 32 and U 33 imino resonances are exchange broadened. The results suggest that ψ 32 functions to preserve the stem integrity in the presence of additional loop modifications or after reorganization of the loop into a translationally functional conformation. 相似文献
15.
The supercritical concentration of CO 2 (SCCO 2) and a high concentration (3.0%) of molecules of hydrogen peroxide (H 2O 2) are currently being used as antiseptic and antibacterial agents. The fact that low concentrations of CO 2 have an activation effect on functional activity of microbes allows us to predict that CO 2 could elevate the toxic effect of H 2O 2 on cells. To check this hypothesis the dependency of the toxic effect of H 2O 2 on wild type of Escherichia coli
K- 12 on soluble concentration of CO 2 in culture media was studied. The obtained data show that culture media enriched with CO 2 leads to the increase of toxic effect of H 2O 2 on microbes at both cases when pH is constant and when it changes. So CO 2 in non-supercritical concentration could elevate the toxic effect of H 2O 2 on microbes by the activation of the metabolic processes in microbes. During the experiments we used classical microbiological
methods (indirect viable cell counts or counting colony forming units (CFUs)), as well as the method of measuring hydrogen
peroxide content in aqueous solution by means of enhanced chemiluminescence method in a peroxidase-luminol- p-iodophenol system. This discovery is concerning to use CO 2/H 2O 2 combination system, which could have implication in the inhibition of growth of microbes in water and the microbiological
monitoring of water could provide valuable information for managing the health of exhibition of aqua ecosystems. 相似文献
17.
The kinetics of charge recombination in Photosystem I P 700-F A/F B complexes and P 700-F X cores lacking the terminal iron?sulfur clusters were studied over a temperatures range of 310 K to 4.2 K. Analysis of the charge recombination kinetics in this temperature range allowed the assignment of backward electron transfer from the different electron acceptors to P 700+. The kinetic and thermodynamic parameters of these recombination reactions were determined. The kinetics of all electron transfer reactions were activation-less below 170 K, the glass transition temperature of the water-glycerol solution. Above this temperature, recombination from [F A/F B] ? in P 700-F A/F B complexes was found to proceed along two pathways with different activation energies (E a). The charge recombination via A 1A has an E a of ~290 meV and is dominant at temperatures above ~280 K, whereas the direct recombination from F X? has an E a of 22 meV and is prevalent in the 200 K to 270 K temperature range. Charge recombination from the F X cluster becomes highly heterogeneous at temperatures below 200 K. The conformational mobility of Photosystem I was studied by molecular dynamics simulations. The F X cluster was found to ‘swing’ by ~30° along the axis between the two sulfur atoms proximal to F A/F B. The partial rotation of F X is accompanied by significant changes of electric potential within the iron?sulfur cluster, which may induce preferential electron localization at different atoms of the F X cluster. These effects may account for the partial arrest of forward electron transfer and for the heterogeneity of charge recombination observed at the glass transition temperature. 相似文献
18.
The remarkable properties of pristine B3O3 nanosheet as a nanocarrier for adsorption and desorption of TEPA anticancer drug for designing potential drug delivery platform were investigated using periodic DFT calculations. We studied the adsorption energy of all stable complexes formed between the drug molecule and B3O3 in gas and aqueous phases along with electronic structure analysis of complexes. Different adsorption configurations were studied for drug/B3O3 complexes, including the interaction of the C atom of the triangular ring, O atom in the TEPA drug with the B atom in B3O3, and indirect drug interaction the middle of the R1 ring cavity of the B3O3 nanosheet. The take-up of TEPA prompts a substantial change of 68.13% in the band gap (Eg) of the B3O3 nanosheet in the most stable complex. The present study results affirmed the application of B3O3 nanosheet as a potential vehicle for TEPA drugs in the treatment of cancerous tissues. 相似文献
19.
A critical point in the V 1 sector and entire V 1V O complex is the interaction of stalk subunits G (Vma10p) and E (Vma4p). Previous work, using precipitation assays, has shown that both subunits form a complex. In this work, we have analysed the N-terminal segment of subunit G (G 1–59) of the V 1V O ATPase from Saccharomyces cerevisiae by using nuclear magnetic resonance (NMR) spectroscopy. Analyses of 1H- 15N heteronuclear single quantum coherence (HSQC) spectra of G 1–59 in the absence and presence of the N-terminal peptides E 1–18 and E 18–38 as well as the produced and purified C-terminal segment (E 39–233) shows specific interactions only with the peptide fragment E 18–38. The binding of this peptide occurs via the residues M 1, V 2, S 3, and K 5 as well for V 22, S 23, K 24, A 25 and R 26 of G 1–59. The specific E 18–38/G 1–59 binding has been confirmed by fluorescence correlation spectroscopy data. The E 18–38 peptide has been studied by CD spectroscopy and NMR. The 3D structure of this peptide adopts a stable helix-hinge-helix formation in solution. A model structure of the E 18–38/G 1–59 complex reveals the orientation of E 18–38 relative to G 1–59 via salt-bridges of the polar residues and van der Waals forces at the very N-terminus of both segments. 相似文献
20.
The genus Flaveria shows evidence of evolution in the mechanism of photosynthesis as its 21 species include C 3, C 3-C 4, C 4-like, and C 4 plants. In this study, several physiological and biochemical parameters of photosynthesis and photorespiration were measured in 18 Flaveria species representing all the photosynthetic types. The 10 species classified as C 3-C 4 intermediates showed an inverse continuum in level of photorespiration and development of the C 4 syndrome. This ranges from F. sonorensis with relatively high apparent photorespiration and lacking C 4 photosynthesis to F. Among the intermediates, the photosynthetic CO2 compensation points at 30°C and 1150 micromoles quanta per square meter per second varied from 9 to 29 microbars. The values for the three C 4-like species varied from 3 to 6 microbars, similar to those measured for the C 4 species. The activities of the photorespiratory enzymes glycolate oxidase, hydroxypyruvate reductase, and serine hydroxymethyltransferase decreased progressively from C 3 to C 3-C 4 to C 4-like and C 4 species. On the other hand, most intermediates had higher levels of phosph enolpyruvate carboxylase and NADP-malic enzyme than C 3 species, but generally lower activities compared to C 4-like and C 4 species. The levels of these C 4 enzymes are correlated with the degree of C 4 photosynthesis, based on the initial products of photosynthesis. Another indication of development of the C 4 syndrome in C 3-C 4 Flaveria species was their intermediate chlorophyll a/b ratios. The chlorophyll a/b ratios of the various Flaveria species are highly correlated with the degree of C 4 photosynthesis suggesting that the photochemical machinery is progressively altered during evolution in order to meet the specific energy requirements for operating the C 4 pathway. In the progression from C 3 to C 4 species in Flaveria, the CO 2 compensation point decreased more rapidly than did the decrease in O 2 inhibition of photosynthesis or the increase in the degree of C 4 photosynthesis. These results suggest that the reduction in photorespiration during evolution occurred initially by refixation of photorespired CO 2 and prior to substantive reduction in O 2 inhibition and development of the C 4 syndrome. However, further reduction in O 2 inhibition in some intermediates and C 4-like species is considered primarily due to the development of the C 4 syndrome. Thus, the evolution of C 3-C 4 intermediate photosynthesis likely occurred in response to environmental conditions which limit the intercellular CO 2 concentration first via refixation of photorespired CO 2, followed by development of the C 4 syndrome. 相似文献
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