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排序方式: 共有316条查询结果,搜索用时 31 毫秒
1.
In vitro stimulation of intact rat posterior pituitary by either veratridine or K+ depolarization results in the concomitant release of neurophysins and in a decrease (70-80%) in their carboxyl methylation as measured either with L-[methyl-3H]methionine in the intact lobes after stimulation or in their homogenates with [methyl-3H]S-adenosyl-L-methionine and purified protein carboxyl methyltransferase. A similar reduction in neurophysin methylation (60%) was observed when the arrival of newly synthesized neurophysins at the posterior pituitary was blocked by colchicine. Experimental data indicate that the reduction in neurophysin content of the lobes after 12 h of colchicine treatment (less than 7%) or after in vitro stimulation (about 10%) cannot account for the marked reduction in neurophysin methylation. The results suggest that the granule pool characterized by rapid turnover of neurophysins probably represents the major source of methyl acceptor proteins in the lobe. In spite of the marked reduction in neurophysin methyl accepting capacity observed after stimulation, there was no parallel increase in methyl accepting capacity of the released neurophysins. We propose that a neurophysin subfraction that might be associated with the membrane of releasable granules participates in the methylation reaction in situ. 相似文献
2.
External ATP enhanced stomatal opening of Commelina communis L. differently from EDTA. ATP was more effective in opening stomata than EDTA, when both were applied in amounts yielding equivalent free Ca2+ concentration. The stimulation by ATP depended upon its de-phosphorylation and was not due to the P1 released. Hence an energetical contribution of external ATP appears possible. Increase in CO2 concentration increased the stimulation of stomatal opening by ATP and diminished the internal ATP level, ATP/(ADP+AMP) ratio and respiration rate. 相似文献
3.
Sarafotoxin receptors mediate phosphoinositide hydrolysis in various rat brain regions 总被引:4,自引:0,他引:4
Sarafotoxin-b, a potent snake vasoconstrictor peptide homologous to the mammalian endothelial vasoconstrictor endothelin, induces phosphoinositide (PI) hydrolysis in various brain regions of the rat. Sarafotoxin-b induced PI hydrolysis is largely independent of extracellular Ca2+ and is detected in all brain regions where toxin-binding sites are found. These results point to the existence of a hitherto undetected neuroreceptor associated with the PI cycle. 相似文献
4.
Immunological and structural characterization of sarafotoxin/endothelin family of peptides 总被引:1,自引:0,他引:1
G Fleminger D Bousso-Mittler A Bdolah Y Kloog M Sokolovsky 《Biochemical and biophysical research communications》1989,162(3):1317-1323
A highly specific and sensitive radioimmunoassay (RIA) was developed for the potent vasoconstrictor peptides, sarafotoxin-b and human endothelin. The antigenic determinants of the antibodies employed in studies with these assays were found to be localized within the amino acid sequence at positions 4-7. This was confirmed by CNBr cleavage of the methionyl residue at position 6 in the sarafotoxin and at position 7 in the endothelin. The chemically characterized modified peptides showed very low cross reactivity in the RIAs. On the other hand, the binding properties as well as the ability to induce phosphoinositide hydrolysis were very similar in the modified and native peptides, indicating that despite cleavage of the peptide bond the biologically active conformation responsible for either binding or phosphoinositide hydrolysis is retained, probably because of the disulfide bonds. Thus, structural alteration might be a valuable means of curtailing some of the various activities induced by the sarafotoxin/endothelin family of peptides. 相似文献
5.
Functional endothelin/sarafotoxin receptors in the rat uterus 总被引:6,自引:0,他引:6
D Bousso-Mittler Y Kloog Z Wollberg A Bdolah E Kochva M Sokolovsky 《Biochemical and biophysical research communications》1989,162(3):952-957
Functional receptors for the peptides of the endothelin (ET) and sarafotoxin (SRTX) families were detected in the rat uterus. These receptors specifically bind 125I-SRTX-b (Bmax = 220 fmol/mg protein), as well as ET-1, ET-3 and SRTX-c (IC50's 10, 5, 300 and 780 nM, respectively). Activation of the uterine ET/SRTX receptors induced dose-dependent phosphoinositide (PI) hydrolysis and three typical contractile responses: 1) increase in the muscle tonic tension; 2) increase in frequency of the spontaneous rhythmic contractions; 3) decrease of relaxation in each spontaneous rhythmic cycle. All three effects appeared at doses as low as 0.5-1 nM. Dose responses yield ED50 values of 5.5, 30 and 680 nM for ET-1, SRTX-b and ET-3, respectively. SRTX-c was the least effective peptide in achieving decrease in relaxation. In view of these results, and since the uterine responses to the peptides were almost immediate and reversible, we suggest that the functional ET/SRTX receptor of the rat uterus that is coupled to PI hydrolysis may be of physiological significance. 相似文献
6.
Solubilization of Rat Brain Phencyclidine Receptors in an Active Binding Form That Is Sensitive to N-Methyl-d-Aspartate Receptor Ligands 总被引:5,自引:3,他引:2
Phencyclidine (PCP) receptors were successfully solubilized from rat forebrain membranes with 1% sodium cholate. Approximately 58% of the initial protein and 20-30% of the high-affinity PCP binding sites were solubilized. The high affinity toward PCP-like drugs, the stereo-selectivity of the sites, and the sensitivity to N-methyl-D-aspartate (NMDA) receptor ligands were preserved. Binding of the potent PCP receptor ligand N-[3H][1-(2-thienyl)cyclohexyl] piperidine ([3H]TCP) to the soluble receptors was saturable (KD = 35 nM), and PCP-like drugs inhibited [3H]TCP binding in a rank order of potency close to that observed for the membrane-bound receptors; the most potent inhibitors were TCP (Ki = 31 nM) and the anticonvulsant MK-801 (Ki = 50 nM). The NMDA receptor antagonist 2-amino-5-phosphonovaleric acid inhibited binding of [3H]TCP to the soluble receptors; glutamate or NMDA diminished this inhibition in a dose-dependent manner. Taken together, the results indicate that the soluble PCP receptor preparation contains the glutamate recognition sites and may represent a single receptor complex for PCP and NMDA, as suggested by electrophysiological data. The successful solubilization of the PCP receptors in an active binding form should now facilitate their purification. 相似文献
7.
Hideyuki Takahashi Mitsuharu Inaki Koichi Fujimoto Shigeru Katsuta Izumi Anno Mamoru Nütsu Yuji Itai 《European journal of applied physiology and occupational physiology》1995,71(5):396-404
We examined the effect of differences in exercise intensity on the time constant (t
c) of phosphocreatine (PCr) resynthesis after exercise and the relationships betweent
c and maximal oxygen uptake (VO2max) in endurance-trained runners (n = 5) and untrained controls (n = 7) (average VO2max = 66.2 and 52.0 ml · min–1 · kg–1, respectively). To measure the metabolism of the quadriceps muscle using phosphorus nuclear magnetic resonance spectroscopy, we developed a device which allowed knee extension exercise inside a magnet. All the subjects performed four types of exercise: light, moderate, severe and exhausting. The end-exercise PCr: [PCr + inorganic phosphate (Pi)] ratio decreased significantly with the increase in the exercise intensity (P < 0.01). Although there was little difference in the end-exercise pH, adenosine diphosphate concentration ([ADP]) and the lowest intracellular pH during recovery between light and moderate exercise, significant changes were found at the two higher intensities (P < 0.01). These changes for runners were smaller than those for the controls (P < 0.05). The
c remained constant after light and moderate exercise and then lengthened in proportion to the increase in intensity (P < 0.05). The runners had a lowert
c at the same PCr and pH than the controls, particularly at the higher intensity (P < 0.05). There was a significant correlation betweent
c and [ADP] in light exercise and betweent
c and both end-exercise PCr and pH in severe and exhausting exercise (P < 0.05). The threshold of changes in pH andt
c was a PCr: (PCr + Pi) ratio of 0.5. There was a significant negative correlation between the VO2max andt
c after all levels of exercise (P<0.05).However, in the controls a significant correlation was found in only light and moderate exercise (P < 0.05). These findings suggest the validity of the use oft
c at an end-exercise PCr:(PCr + Pi) ratio of more than 0.5 as a stable index of muscle oxidative capacity and the correlation between local and general aerobic capacity. Moreover, endurance-trained runners are characterized by the faster PCr resynthesis at the same PCr and intracellular pH. 相似文献
8.
Fatty acid incorporation increases the affinity of muscarinic cholinergic receptors for agonists 总被引:1,自引:0,他引:1
Incorporation of unsaturated fatty acids into membrane fragments from rat brain cortex and medulla pons selectively increased the affinity of the muscarinic agonist, carbamylcholine. The affinity and number of binding sites for the labeled antagonist, N-[3H]methyl-4-piperidyl benzilate was unchanged. The effect on agonist binding was most prominent in the cortex, in which carbamylcholine IC50 values were decreased up to 5-fold. Selectivity of the effect was observed with fatty acids of chain length 18-20 carbons, unsaturation in position 11-12, and a cis conformation of the double bond being most effective. The effects of fatty acids on agonist binding were due primarily to alterations in the affinity constants for the binding reaction, with minor increases in the proportion of high-affinity sites. Transition metals selectively increased the percentage of high-affinity sites in the cortex, but in cis-vaccenic-acid-treated membranes more than additive effects of the metal were observed; both were reversed by GTP. GTP also reversed binding parameters in cis-vaccenic-acid-treated medulla membranes to control level. We conclude that the primary effect of the active fatty acids is to alter the thermodynamic properties of muscarinic agonist binding without markedly inducing interconversion. 相似文献
9.
A three-dimensional model of DNA/RNA triple helix that contains a poly(L-deoxyadenosine) (L-dA) chain is proposed based on computer-assisted model building and energy calculations. The model building was performed by a new method that systematically searches possible conformations of nucleotide units in the helical chains. Two possible orientations of sugar-phosphate chains, in which two homopyrimidine strands are parallel or antiparallel with each other, were considered in the systematic search. Several possible base-pairing models, in which there are one Watson-Crick base pair and one other base pair, were also considered. Many possible models selected by the systematic search were further refined through molecular mechanics calculation incorporating a helical boundary condition. The preferred model, which was selected on the basis of potential energy, was the one with Watson-Crick and Hoogsteen base pairs and with its two polypyrimidine chains in the antiparallel orientation. The model can explain the experimental observation that poly(L-dA) forms a stable triple helix with poly(uridylic acid) (U) but not with poly(deoxythymidylic acid) (dT). 相似文献
10.
Motoyuki Nakamura Yorihiko Koeda Fumitaka Tanaka Toshiyuki Onoda Kazuyoshi Itai Masaki Ohsawa Kozo Tanno Kiyomi Sakata Shinich Omama Yasuhiro Ishibashi Shinji Makita Mutsuko Ohta Kuniaki Ogasawara Takashi Komatsu Akira Okayama 《PloS one》2013,8(12)