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1.
This paper describes a [15N,1H]/[13C,1H]-TROSY experiment for the simultaneous acquisition of the heteronuclear chemical shift correlations of backbone amide 15N–1H groups, side chain 15N–1H2 groups and aromatic 13C–1H groups in otherwise highly deuterated proteins. The 15N–1H and 13C–1H correlations are extracted from two subspectra of the same data set, thus preventing possible spectral overlap of aromatic and amide protons in the 1H dimension. The side-chain 15N–1H2 groups, which are suppressed in conventional [15N,1H)-TROSY, are observed with high sensitivity in the 15N–1H subspectrum. [15N,1H]/[13C,1H]-TROSY was used as the heteronuclear correlation block in a 3D [1H,1H]-NOESY-[15N,1H]/[13C,1H]-TROSY experiment with the membrane protein OmpA reconstituted in detergent micelles of molecular weight 80000 Da, which enabled the detection of numerous NOEs between backbone amide protons and both aromatic protons and side chain 15N–1H2 groups. 相似文献
2.
The cyclo7,10[Cys7,Cys10,Nle12], cyclo7,10[Cys7,D -Ala9,Cys10,Nle12], and cyclo7,10[Cys7,L -Ala9,Cys10,Nle12] analogues of the α-factor mating pheromone (WHWLQLKPGQPMY) of the yeast Saccharomyces cerevisiae were studied in DMSO/water (80 : 20) and aqueous solution by nmr spectroscopy. In addition, the cyclo7,10[Cys7,D -Val9,Cys10,Nle12] α-factor was examined in DMSO/water. Nuclear Overhauser effect (NOE) and NH dδ/dT data indicate that the cyclo7,10[Cys7,D -Val9,Cys10,Nle12] α-factor adopts a type II β-turn in DMSO/water and that the cyclo7,10[Cys7,D -Ala9,Cys10,Nle12] - and cyclo7,10-[Cys7,L -Ala9,Cys10,Nle12] α-factor analogues adopt type II and type I/III β-turns, respectively, in both DMSO/water and aqueous solutions. In aqueous solution, residues 8 and 9 of the cyclo7,10[Cys7,Cys10,Nle12] α-factor appear to adopt at least two distinct conformations, one of these being identified as a type I/III β-turn. In contrast, the cyclo7,10[Cys7,Cys10,Nle12] α-factor appears to adopt predominately a type II β-turn in DMSO/water. Quantitative NOE measurements of the cyclo7,10[Cys7,Cys10,Nle12]-, cyclo7,10[Cys7,D -Val9,Cys10,Nle12]-, and cyclo7,10[Cys7,L -Ala9,Cys10,Nle12] α-factors in DMSO/water were used to derive three-dimensional structures of the cyclo7,10[Cys7,Pro8,X9Cys10] portion of these analogues. © 1994 John Wiley & Sons, Inc. 相似文献
3.
Yuan Zhuang Liu-sheng Peng Yong-liang Zhao Yun Shi Xu-hu Mao Gang Guo Weisan Chen Xiao-fei Liu Jin-yu Zhang Tao Liu Ping Luo Pei-wu Yu Quan-ming Zou 《Cancer immunology, immunotherapy : CII》2012,61(11):1965-1975
IL-22-producing CD4+ T cells (IL-22+CD4+ T cells) and Th22 cells (IL-22+IL-17?IFN-γ?CD4+ T cells) represent newly discovered T-cell subsets, but their nature, regulation, and clinical relevance in gastric cancer (GC) are presently unknown. In our study, the frequency of IL-22+CD4+ T cells in tumor tissues from 76 GC patients was significantly higher than that in tumor-draining lymph nodes, non-tumor, and peritumoral tissues. Most intratumoral IL-22+CD4+ T cells co-expressed IL-17 and IFN-γ and showed a memory phenotype. Locally enriched IL-22+CD4+ T cells positively correlated with increased CD14+ monocytes and IL-6 and IL-23 detection ex vivo, and in vitro IL-6 and IL-23 induced the polarization of IL-22+CD4+ T cells in a dose-dependent manner and the polarized IL-22+CD4+ T cells co-expressed of IL-17 and IFN-γ. Moreover, IL-22+CD4+ T-cell subsets (IL-22+IL-17+CD4+, IL-22+IL-17?CD4+, IL-22+IFN-γ+CD4+, IL-22+IFN-γ?CD4+, and IL-22+IL-17+IFN-γ+CD4+ T cells), and Th22 cells were also increased in tumors. Furthermore, higher intratumoral IL-22+CD4+ T-cell percentage and Th22-cell percentage were found in patients with tumor-node-metastasis stage advanced and predicted reduced overall survival. In conclusion, our data indicate that IL-22+CD4+ T cells and Th22 cells are likely important in establishing the tumor microenvironment for GC; increased intratumoral IL-22+CD4+ T cells and Th22 cells are associated with tumor progression and predict poorer patient survival, suggesting that tumor-infiltrating IL-22+CD4+ T cells and Th22 cells may be suitable therapeutic targets in patients with GC. 相似文献
4.
Bacillus thuringiensis produces several larvicidal crystalline inclusions during sporulation. An understanding of their mechanisms of action is
commercially important. In this study, two toxins, Cry1Ab and Cry1Ac, were compared that showed 98% amino acid identity in
domain I and II, but differed significantly in domain III. Using site-directed mutagenesis techniques, two conserved loop
2 Arg's (368RR369) of Cry1Ab and Cry1Ac toxins were replaced with Ala (368AR369, 368RA369, 368AA369), Glu (368EE369), Phe (368FF369), His (368HH369), and Lys (368KK369). The effect of these mutants on structural stability, larvicidal potency, receptor binding, and ionic permeability towards
two important cotton pests, pink bollworm (Pectinophora gossypiella) and bollworm (Helicoverpa zea) were analyzed. All seven mutants of Cry1Ab, excluding 368AR369, produced a stable protoxin, whereas for Cry1Ac all seven mutants yielded stable protoxin. Results showed that all the stable
mutants behaved similarly to the wild type on incubation with trypsin and gut extract of both insect larvae. The Cry1Ab mutants,
368AR369, 368AA369, 368FF369, and 368HH369, lost toxicity; 368EE369 had reduced toxicity; whereas the more conserved change 368KK369 retained the toxicity similar to the wild type towards P. gossypiella. Double mutants of Cry1Ac, 368AA369 and 368FF369, abolished the toxicity. Double mutant 368KK369 of Cry1Ac retained its toxicity against P. gossypiella, whereas single mutants 368AR369, 368RA369, and 368HH369 retained only reduced toxicity. All the mutants of Cry1Ab lost their toxicity against H. zea except 368KK369. In Cry1Ac single mutants, 368AR369 and 368RA369, reduction in the toxicity was observed. A double mutant of Cry1Ac, 368KK369, also retained reduced toxicity. All the other double mutants lost their toxicity. Voltage clamping experiments on H. zea midguts provided an additional evidence about the insecticidal property and inhibition of Isc across the transepithelial membrane of the insect midgut.
Received: 5 June 2000 / Accepted: 5 July 2000 相似文献
5.
《International journal of radiation applications and instrumentation. Part B, Nuclear medicine and biology》1987,14(2):143-151
Tumor uptake rates, concentrations in mitochondrial fraction (containing lysosome) of liver and tumors, avid accumulations in connective tissue (especially inflammatory tissue) and binding substances in these tissues for 46Sc3+ and 51Cr3+ were essentially similar to those for 67Ga3+, 111In3+, 169Yb3+, 167Tm3+, 95Zr4+ and 181Hf4+. However, the main binding substance of 46Sc3+ and 51Cr3+ in tumor and liver was the acid mucopolysaccharide (as described concerning 95Zr and 181Hf) whose molecular weight exceeded 40,000, although the main binding substance of 67Ga3+, 111In3+, 169Yb3+ and 167Tm3+ was the acid mucopolysaccharide with a molecular weight of about 10,000. 相似文献
6.
T Shibasaki L Deftos R Guillemin 《Biochemical and biophysical research communications》1979,90(4):1266-1273
Fifteen analogs of luliberin (2, LRH) were synthesized by the solid phase method and examined for their ability to block ovulation in the rat. Two analogs, [Ac-DAla1,DPhe2,DTrp3,6]-LRH and [Ac-DPhe1,DPhe2,DTrp3,6]-LRH, each blocked ovulation at a single injection dose of 250 μg administered at noon on the day of proestrus; three peptides, [Ac-DPro1,DPhe2,DTrp3,6]-LRH, [Ac-DThi1,DPhe2,DTrp3,6]-LRH and [Ac-DTrp1,DPhe2,DTrp3,6]-LRH, were effective at doses of 500 μg each; and four others, [Ac-DTrp1,DPhe2,DTrp3,DTrp(Nps)6]-LRH, [Chlorambucil-DPhe1, DPhe2, DTrp3,6]-LRH, [1,DThi2,DTrp3,6]-LRH and [(2-DLys6]-LRH, gave partial inhibition at doses tested. 相似文献
7.
8.
Red blood cells (RBCs) are probably the most common target through the damaging action of reactive oxygen species on the cells. The photohemolysis activity of m-chloroperbenzoic acid (CPBA) was concentration- and exposure time-dependent. Twenty minutes photo exposure time and 200?μm of CPBA concentration were optimum to study the effect of generated superoxide (O2-) and hydroxyl (?OH) radicals on RBCs. RBCs lysis photosensitized by CPBA was investigated in the presence of [(VL2O)(VL2H2O)]Cl6, [MnL2O]2Cl42H2O, [FeL2Cl2]Cl H2O, [CoL2Cl2]4H2O or [ZnL2Cl2]H2O respectively, where L is 2-methylaminopyridine, with SOD-mimetic activities with the aim of ascertaining their protective activity towards the photo induced cell damage. The decrease of photolytic activity caused by these complexes was concentration-dependent and the maximum percentage of protective activity was 75, 70, 68, 57 or 24% for [(VL2O)(VL2H2O)]Cl6, [MnL2O]2Cl4 2H2O, [FeL2Cl2]Cl H2O, [CoL2Cl2]4H2O or [ZnL2Cl2]H2O complex respectively, against the cell irradiated without addition of metal complexes. The comparison between the decrease of photolytic activity caused by these complexes and their SOD-mimetic activity of these metal complexes showed an appreciable correlation. 相似文献
9.
Na+-ATPase of high-K+ and low-K+ sheep red cells was examined with respect to the sidedness of Na+ and K+ effects, using inside-out membrane vesicles and very low ATP concentrations (?2 μM). With varying amounts of Na+ in the medium, i.e., at the cytoplasmic surface, Nacyt+, the activation curves show that high-K+ Na+-ATPase has a higher affinity for Nacyt+ compared to low-K+. The apparent affinity for Nacyt+ is also increased by increasing the ATP concentrations in high-K+ but not low-K+. With Nacyt+ present, Na+-ATPase is stimulated by intravesicular Na+, i.e., Na+ at the originally external surface, Naext+, to a greater extent in low-K+ than high-K+. Intravesicular K+ (Kext+) activates Na+-ATPase in high-K+ but not in low-K+ vesicles and extravesicular K+ (Kcyt+) inhibits low-K+ but not high-K+ Na+-ATPase. Thus, the genetic difference between high-K+ and low-K+ is expressed as differences in apparent affinities for both Na+ and K+ and these differences are evident at both cytoplasmic and external membrane surfaces. 相似文献
10.
Yoshio Ikeda Kazuwa Nakao Takaaki Yoshimasa Noboru Yanaihara Shosaku Numa Hiroo Imura 《Biochemical and biophysical research communications》1982,107(2):656-662
High performance liquid chromatography (HPLC) coupled with specific radioimmunoassays for methionine-enkephalin-Arg6-Gly7-Leu8 (Met-E-Arg6-Gly7-Leu8), methionine-enkephalin (Met-E), leucine-enkephalin (Leu-E) and methionine-enkephalin-Arg6-Phe7 (Met-E-Arg6-Phe7) has demonstrated that Met-E-Arg6-Gly7-Leu8 exists together with Met-E, Leu-E and Met-E-Arg6-Phe7 in the brain of guinea pig, rat and golden hamster. The content of Met-E-Arg6-Gly7-Leu8 was comparable to those of Leu-E and Met-E-Arg6-Phe7, whereas that of Met-E was the highest among the four opioid peptides. These results are compatible with the recent studies on the nucleotide sequence of cloned cDNA for preproenkephalin from bovine adrenal medulla, which reveal that this precursor molecule contains four copies of Met-E and one copy each of Leu-E, Met-E-Arg6-Phe7 and Met-E-Arg6-Gly7-Leu8. The co-existence of Met-E-Arg6-Gly7-Leu8 with Met-E, Leu-E and Met-E-Arg6-Phe7 suggests that their biosynthetic pathway in the brain is similar to that in the adrenal medulla. 相似文献
11.
Summary The distribution and characterization of the opioid octapeptide met5-enkephalin-arg6-gly7-leu8 (met5-enk-arg6-gly7-leu8) within the gastrointestinal tract of the rat has been determined by immunohistochemistry and radioimmunoassay by use of a newly developed antibody to met5-enk-arg6-gly7-leu8. With both techniques, met5-enk-arg6-gly7-leu8-immunoreactivity (met5-enk-arg6-gly7-leu8IR) was detected in all regions of the gastrointestinal (GI) tract except the esophagus. The highest concentration of immunoreactive met5-enk-arg6-gly7-leu8 was observed in the colon, while intermediate concentrations were found in the stomach, duodenum, jejunum, and ileum. Immunostained somata were observed chiefly in the myenteric plexus; immunostained processes were present primarily in the myenteric plexus and the circular muscle layer. This distribution pattern is similar to that previously observed with antiserum to met5-enkephalin-arg6-phe7 (met5-enk-arg6phe7). Chromatographic analysis of met5-enk-arg6-gly7leu8-immunoreactive peptides extracted from the GI tract revealed the presence of an immunoreactive peptide of high molecular weight which accounted for approximately three-quarters of met5-enk-arg6-gly7-leu8-IR in both stomach and colon. These findings suggest a role for peptides related to the octapeptide met5-enk-arg6-gly7-leu8 in the regulation of GI function. 相似文献
12.
A set of three experiments is described which correlate aromatic resonances of histidine and tryptophan residues with amide
resonances in 13C/15N-labelled proteins. Provided that backbone 1H and 15N positions of the sequentially following residues are known, this results in sequence-specific assignment of histidine 1Hδ2/13Cδ2 and 1Hε1/13Cε1 as well as tryptophan 1Hδ1/13Cδ1, 1Hζ2/13Cζ 2, 1Hη2/13Cη2, 1Hε3/13Cε3, 1Hζ3/13Cζ3 and 1Hε1/15Nε1 chemical shifts. In the reverse situation, these residues can be located in the 1H–15N correlation map to faciliate backbone assignments. It may be chosen between selective versions for either of the two amino
acid types or simultaneous detection of both with complete discrimination against phenylalanine or tyrosine residues in each
case. The linkages between δ-proton/carbon and the remaining aromatic as well as backbone resonances do not rely on through-space
interactions, which may be ambiguous, but exlusively employ one-bond scalar couplings for magnetization transfer instead.
Knowledge of these aromatic chemical shifts is the prerequisite for the analysis of NOESY spectra, the study of protein–ligand
interactions involving histidine and tryptophan residues and the monitoring of imidazole protonation states during pH titrations.
The new methods are demonstrated with five different proteins with molecular weights ranging from 11 to 28 kDa. 相似文献
13.
We have previously reported on the biochemical properties of a Na+,K+,2Cl?-cotransport in HeLa cells and here we deal with aspects of its physiological regulation. Na+,K+,2Cl?-cotransport in HeLa cells was studied by 86Rb+ influx and 86Rb+/22Na+ efflux measurements. The effects of rat atrial natriuretic peptide (ANP), isoproterenol, and amino acids on 86Rb+ flux, mediated by the bumet-anide-sensitive Na+, K+, 2Cl?-cotransport system and the ouabain-sensitive Na+/K+-pump, were investigated. ANP reduced bumetanide-sensitive 86Rb+ influx under isotonic as well as under hypertonic conditions. Similar decrease of bumetanide-sensitive 86Rb+ influx was observed in the presence of 8-bromo-cGMP, while neither isoproterenol as a β-receptor agonist nor 8-bromo-cAMP-could alter bumetanide-sensitive 86Rb+ influx. Furthermore, efflux of 86Rb+ and 22Na+ was greatly reduced in the presence of bumetanide and ANP. Together with our recent findings, showing functionally active, high affinity receptors for ANP on HeLa cells (Kort and Koch, Biochim. Biophys. Res. Commun. 168:148–154, 1990), this study indicates that ANP participates in the regulation of the Na+, K+, 2Cl?-cotransport system in HeLa cells. Further measurements revealed that amino acids as present in the growth medium (Joklik's minimal essential medium) and the amino acid derivative α-methyl-aminoisobutyric acid (metAlB, 1 and 5 mM, respectively) also reduced Na+, K+, 2Cl?-cotransport-mediated 86Rb+ uptake and diminished the stimulatory effect of hypertonicity on the cotransporter. In addition, the Na+/K+-pump was markedly stimulated in the presence of amino acids, while neither ANP and 8-Br-cGMP nor isoproterenol and 8-Br-cAMP had a significant effect on the activity of the Na+/K+-pump. 相似文献
14.
S. Fesenko E. Fesenko I. Titov E. Karpenko N. Sanzharova A. Gondin Fonseca J. Brown 《Radiation and environmental biophysics》2010,49(4):531-547
An extensive programme of experiments on transfer of radionuclides to aquatic species was conducted in the former USSR starting
from the early 1950s. Only a few of these studies were made available in the English language literature or taken into account
in international reviews of radionuclide behaviour in marine ecosystems. Therefore, an overview of original information on
radionuclide transfer to marine biota species available from Russian language literature sources is presented here. The concentration
ratio (CR) values for many radionuclides and for marine species such as: 239Pu, 106Ru and 95Zr (crustacean), 54Mn, 90Sr, 95Nb, 106Ru, 137Cs 239Pu, 241Am and natural U (molluscs), and 54Mn, 90Sr, 137Cs and 144Ce (fish) are in good agreement with those previously published, whilst for some of them, in particular, for 32P and 110Ag (crustaceans), 35S (molluscs), 32P, 35S, 95Nb, and 106Ru (macroalgae) and 60Co and 239,240Pu (fish) the data presented here suggest that changes in the default CR reference values presented in recent marine reviews
may be required. The data presented here are intended to supplement substantially the CR values being collated within the
handbook on Wildlife Transfer Coefficients, coordinated under the IAEA EMRAS II programme. 相似文献
15.
《Journal of biochemical and biophysical methods》1995,30(2-3):163-177
The dynamics of the opening-closing of the constituent base-pairs as well as of the exchange kinetics of the base-paired imino and amino protons with water in a DNA-RNA hybrid, [5′r(G1A2U3U4G5A6A7)3′]:5′p[d(T8C9A10A11T12C13)]3′-Pzn] duplex (I), are reported here in details for the first time. The exchange kinetics of amino and imino protons in the DNA-RNA hybrid (duplex I) have been compared with identical studies on the following B-DNA duplexes: d(C1G2T3A4C5G6)2 (II), d[p(5′T1G2T3T4T5G6 G7C8)3′]:d[p(5′C9C10A11A12A13C14A15)3′] (III), d(C5G6C7G8A9A10T11T12C13G14C15G16)2 (IV) and d(C1G2C3G4C5G6C7G8A9A10T11T12C13G14C15G16C17G18C19G20)2 (V). This comparative study shows that the life-times τo of various base-pairs in the DNA-RNA hybrid (I) varies in the range of ∼ 1 ms, and they are quite comparable to those of the shorter B-DNA duplexes (II) and (III), but very different from the τo of the larger duplexes (IV) and (V): the τo for the base pair of T11 and T12 residues in the 20-mer (duplex V) are 2.9 ± 2.3 ms and 23.2 ± 8.9 ms, respectively, while the corresponding τo in the 12-mer (duplex IV) are 2.8 ± 2.2 ms and 17.4 ± 5.4 ms. It has also been shown that the total energy of activation (Ea) assessed from the exchange rates of both imino and amino protons, representing energetic contributions from both base-pair and helix opening-closing as well as from the exchange process of the imino protons from the open state with the bound water, is close to the Ea of the short B-DNA duplex (Ea ≈ 28–47 kcal/mol). 相似文献
16.
Extensive conformational analysis of a series of β‐alkyl substituted cyclopeptides—cyclo(Pro1–Xaa2–Nle3–Ala4–Nle5–Pro6–Xaa7–Nle8–Ala9–Nle10) and cyclo[Pro1–Xaa2–Nle3–(Cys4– Nle5–Pro6–Xaa7–Nle8–Cys9)–Nle10] as well as their corresponding unsubstituted core structures cyclo(Pro1–Xaa2–Ala3–Ala4–Ala5–Pro6–Xaa7–Ala8–Ala9–Ala10) and cyclo(Pro1–Xaa2–Ala3–Cys4– Ala5–Pro6–Xaa7–Ala8–Cys9–Ala10) has been performed employing both the ECEPP/2 and the MAB force fields (Xaa = Gly, L ‐Ala, D ‐Ala, Aib, and D ‐Pro). Results show that (a) possible three‐dimensional structures of the cyclo(Pro1–Gly2–Lys3–Ala4–Lys5–Pro6–Gly7–Lys8–Ala9–Lys10) molecule are not limited to a single extended “rectangular” conformation with all Lys side chains oriented at the same side of the molecule; (b) conformational equilibrium in monocyclic analogues obtained by replacements of conformationally flexible Gly residues for L ‐Ala, D ‐Ala, Aib, or D ‐Pro is not significantly shifted towards the target “rectangular” conformational type; and (c) introduction of disulfide bridges between positions 4 and 9 is a very powerful way to stabilize the target conformations in the resulting bicyclic molecules. These findings form the basis for further design of rigidified regioselectively addressable functionalized templates with many application areas ranging from biostructural to diagnostic purposes. © 1999 John Wiley & Sons, Inc. Biopoly 50: 361–372, 1999 相似文献
17.
Celia E. Deane-Drummond 《Physiologia plantarum》1986,66(1):115-121
Net nitrate uptake, 36ClO?3/NO?3 influx and 36Cl? influx into Pisum sativum L. cv. Feltham First seedlings have been examined following growth in culture medium containing different combinations of chloride and nitrate. When young (6 days old) seedlings, that had been grown in the absence of N were used, nitrate accumulation stimulated net nitrate uptake and 36ClO?3/NO?3 influx (r2= 0.99) while chloride accumulation inhibited nitrate uptake and 36ClO?3/NO?3 influx (r2= 0.65). When nitrate was provided during growth there was no effect of chloride pretreatment on net nitrate uptake and there was little effect of total [NO?3+ Cl?]i on 36ClO?3/NO?3 influx (r2= 0.26). A direct effect of Cl? on 36ClO?3/NO?3 influx was only found when seedlings had been starved of N for more prolonged periods (14 days). When moderate chloride was supplied during growth, 36Cl? influx was insensitive to nitrate or chloride accumulated, but significantly correlated with loge [NO?3+ Cl?]i (r2= 0.75). When trace amounts of Cl? were supplied during growth 36Cl? influx was inhibited by (a) NO?3 in the external medium and (b) Cl? pretreatment, but was insensitive to NO?3 pretreatment. The sensitivity of 36Cl? influx to external nitrate was not found following Cl? pretreatment in the absence of nitrate. The possibility that there are two populations of chloride carriers which differ in their sensitivity to external nitrate is discussed. Tentative schematic models to account for the regulation of nitrate and chloride uptake are proposed in the context of current hypotheses for regulation of ion transport and control systems theory. 相似文献
18.
The interaction of K+ with mammalian ribosomes was studied by equilibrium dialysis and compared with that of other univalent cations. The heavy K+ analogue, Tl+, binds more firmly than K+ to ribosomes and, unlike K+, has a practically useful isotope. With 204Tl+ as a marker of K+-selective binding the ribosome-cation interaction could be followed down to levels below 0.1 average Tl+-occupied site per ribosome. The Tl+/ribosome ratio varied with the free Tl+ concentration in a multiple way. At high Tl+ saturation Tl+ was easily displaced by Mg2+. With decreasing Tl+ saturation the competitive activity of Mg++ was strikingly reduced, indicating that Tl+ and Mg++ compete with different efficiency for different classes of sites.The experiments on univalent cations were performed at 1.5 mM Mg2+ under two complementary conditions: (1) Ribosomes were pretreated with 5 × 10?2, 5 × 10?3, and 5 × 10?4 M LiNO3, NaNO3, KNO3, and CsNO3, and then equilibrated with different concentrations of 204TlNO3 in the same buffers. (2) Ribosomes were pretreated with 10?2, 10?4, and 10?6 M 204TlNO3, and then equilibrated with different concentrations of LiNO3, NaNO3, KNO3, and CsNO3 (displacement experiments). At high Tl+ saturation Na+ and Li+ were about as active as K+ and Cs+ in competing with 204Tl+. With decreasing Tl+ saturation a differentiation occurred in favor of K+ and Cs+, with some preference for K+. It is concluded that ribosomes contain a limited number of sites with pronounced ion specificity. Of physiological cations K+ is most firmly bound to these sites. 相似文献
19.
Summary Twelve 24 h bioassay experiments were conducted in 1980 and 1981 to evaluate seasonal influences of NO
3
-
, NH
4
+
, PO
4
3-
, N+P, vitamins, trace metals, a synthetic chelate and common salts on 14C and 15N primary production in Toolik Lake, Alaska. Addition of N+P, NO
3
-
or NH
4
+
significantly increased 14C primary production over all other treatments on most dates. Only on three occasions did any other treatment have any statistically significant effect on 14C primary production. 15NO
3
-
and 15NH
4
+
primary production were each significantly enhanced by PO
4
3-
enrichement relative to all other nutrient applications on seven dates. Significantly depressed 15NO
3
-
primary production consistently resulted from NH
4
+
addition but enrichment with NO
3
-
gave significantly depressed 15NH
4
+
primary production in just three experiments. Other treatments significantly influenced 15N primary production on two occasions only. The general stimulatory influence of N+P, NO
3
-
and NH
4
+
on 14C primary production as well as the similar effect of PO
4
3-
on 15N primary production had no seasonal pattern. The total data show that nitrogen and phosphorus are the most important chemical regulators of primary production in Toolik Lake. 相似文献
20.
The mechanism of the protective effect of Ca2+ on cellular K+ content was studied by examination of the effect of Ca2+ on efflux of the K+ analog, 86Rb+, from preloaded cells with the use of compounds which interfere with monovalent cation movements. Ca2+ decreased 86Rb+ efflux to the same extent in the presence and absence of ouabain, suggesting that Ca2+ did not alter the activity of the (Na+ + K+)-adenosine triphosphatase pump. Ca2+ exerted a similar protective effect in the presence of furosemide, an inhibitor of K+-K+ exchange, indicative that Ca2+ was not inhibiting this pathway. Since Ca2+ did not influence these pathways, it is concluded that Ca2+ exerts its primary effect by slowing passive diffusion. In support of this, Ca2+ also slowed 22Na+ efflux. In addition, ethanol-induced leakage of 86Rb+ was reversed by extracellular Ca2+, suggestive of a Ca2+-membrane phospholipid interaction. 相似文献