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11.
Paracrine functions of the coronary vascular endothelium 总被引:5,自引:0,他引:5
Ingrid Fleming Johann Bauersachs Rudi Busse 《Molecular and cellular biochemistry》1996,157(1-2):137-145
12.
Marc Klein 《Invertebrate neuroscience : IN》1995,1(1):15-24
Up and down-regulation of calcium and potassium conductances are associated with several forms of short-term synaptic modulation.
Detailed investigation of synaptic plasticity in the marine gastropodAplysia, and in other mollusks, indicates that synaptic transmission can be influenced in a number of ways by modulatory neurotransmitters
acting through several second-messenger cascades. Modulation at the synapse itself occurs by means of the regulation of calcium
current as well as through effects on processes directly involved in transmitter mobilization and exocytosis. Modulation of
potassium current plays a major role in controlling neuronal excitability and may contribute to a lesser extent to the regulation
of transmitter release through actions on the resting potential and on action potential configuration. 相似文献
13.
The quantitative content of three transport systems for aromatic amino acids in cells of Halobacterium salinarium was measured: the common system (K
m is about 10-6
M) and two tyrosine-specific systems with high and low affinity (K
m is about 10-8 and 10-5
M, respectively). To determine the activity of each of three systems separately, a method was developed based on the selective phenylalanine effect on these activities. When phenylalanine exeeds [14C]tyrosine by four to sixforld, it inhibits competitively the activity of the common system, and its 50- to 100-fold molar excess is inhibitory in a non-competitive way for the specific high affinity system (HAT system). The specific low affinity system (LAT system) is practically insensitive to phenylalanine. The activities of tyrosine-specific transport systems are slightly dependent on the culture age, and the observed decrease in transport activity during growth is due mainly to the decreased content of the common system. The HAT system formation is regulated by the repression type, and the effectors are aromatic amino acids especially tyrosine itself. The physiological sense of the tyrosine transport system's multiplicity in H. salinarium is discussed. 相似文献
14.
Patrick Doherty Josie Furness Emma J. Williams Frank S. Walsh 《Journal of neurochemistry》1994,62(6):2124-2131
Abstract: Activation of tyrosine kinases is established as an important mechanism for controlling growth cone motility and neurite outgrowth. We have tested the effects of a range of tyrosine kinase inhibitors on neurite outgrowth from postnatal day 4 cerebellar granule cells cultured over confluent monolayers of 3T3 fibroblasts. The only agent that had any effect was herbimycin A, which stimulated neurite outgrowth. The response is shown to be attributable to a direct effect of this tyrosine kinase inhibitor on neurones. The neurite outgrowth response to herbimycin A was inhibited by two other tyrosine kinase inhibitors, which on their own did not affect neurite outgrowth. The data suggest that the response to herbimycin A reflects either a direct or indirect activation of one or more protein tyrosine kinases. Independent signalling events downstream from tyrosine kinase activation underlying the neurite outgrowth response to herbimycin A include increased activity of protein kinase C and calcium influx into neurones through both N-and L-type calcium channels. 相似文献
15.
Abstract: Tyrosine hydroxylase activity was measured under optimal and suboptimal assay conditions in hippocampal extracts from young (2 month), mature (12 month), and old (24 month) Fischer 344 male rats 72 h after the infusion of 200 µg of the neurotoxin 6-hydroxydopamine or vehicle into the lateral ventricle. The lesion resulted in a 45–55% decrease of tyrosine hydroxylase activity measured under optimal conditions (pH 6.1, 3.0 m M 6-methyl-5,6,7,8-tetrahydropterin) and an ∼35% decrease in the relative concentration of immunoreactive tyrosine hydroxylase. When measured under suboptimal conditions (pH 6.6, 0.7 m M 6-methyl-5,6,7,8-tetrahydropterin), tyrosine hydroxylase activity in 2- and 12-month-old lesioned animals was twice that measured in vehicle-treated animals. However, in the old lesioned animals, tyrosine hydroxylase activity measured under suboptimal conditions was not different from that measured in age-matched vehicle-treated animals. Isoforms of tyrosine hydroxylase were identified on immunoblots after two-dimensional gel electrophoresis using enhanced chemiluminescence. The relative proportion of lower pl isoforms of tyrosine hydroxylase in the 2-month-old lesioned animals was greater than that observed in vehicle-treated controls. In contrast, no difference was seen in the relative proportion of tyrosine hydroxylase isoforms in the 24-month-old lesioned versus control animals. These data indicate that the ability of locus ceruleus neurons to rapidly respond to and compensate for insult is attenuated in 24-month-old Fischer 344 rats due to a deficit in stimulus-evoked enzyme phosphorylation. 相似文献
16.
Maurizio Grimaldi Giacomo Pozzoli Pierluigi Navarra Paolo Preziosi Gennaro Schettini 《Journal of neurochemistry》1994,63(1):344-350
Abstract: In this study we analyzed the involvement of the cyclic AMP (cAMP)-protein kinase A system in the regulation of interleukin 6 production by cultured cortical astrocytes. Vasoactive intestinal peptide strongly increased, in a dose-dependent manner, interleukin 6 production. This effect was reduced when protein kinase A was blocked by KT-5720; it was not affected by calphostin C, a protein kinase C inhibitor. Forskolin caused a concentration-dependent increase in interleukin 6 release that was also inhibited by KT-5720. Because prostaglandins are believed to play a role in interleukin 6 production, we tried to determine whether the stimulatory effects of vasoactive intestinal peptide and forskolin on cytokine release might be mediated by stimulation of prostaglandin production in cortical astrocytes. Vasoactive intestinal peptide did not increase the production of either prostaglandin E2 or F2α. Conversely, forskolin concentration-dependently stimulated the production of both prostaglandins, an effect that was blocked by indomethacin. Indomethacin did not affect either vasoactive intestinal peptide- or forskolin-stimulated interleukin 6 production. To exclude the possibility that prostaglandins participate in interleukin 6 production induced by forskolin, we tested prostaglandins E2 and F2α. The former was completely ineffective in eliciting the cytokine production, whereas prostaglandin F2α slightly increased interleukin 6 production only at the highest concentrations. 8-Bromo-cAMP and dibutyryl-cAMP stimulated interleukin 6 production to a lesser extent than vasoactive intestinal peptide and forskolin. In conclusion, we provide evidence that vasoactive intestinal peptide increases interleukin 6 production by astrocytes through the stimulation of the cAMP-protein kinase A pathway, an effect that is reproduced by cAMP analogues. In addition, we point out that prostaglandins are not involved in vasoactive intestinal peptide- and forskolin-mediated induction of interleukin 6 production in cultured astrocytes. 相似文献
17.
Summary Although the regulatory activity of steroid hormones on amino acid metabolism has been described, no information is published on the effect of ovariectomy. We studied the influence of ovariectomy in Wistar rats determining the amino acids phenylalanine and tyrosine in liver, kidney, plasma and urine. 32 animals were used in the study, 12 animals were sham operated, 9 animals were ovariectomized and 11 rats were ovariectomized and supplemented with estradiol. No quantitative changes were detected comparing liver and kidney phenylalanine and tyrosine between the groups (sham operated rats liver phenylalanine 2,53nM/mg ± 1,07; liver tyrosine 1.95nM/mg ± 0.92; kidney phenylalanine 2.16nM/mg ± 0.53; kidney tyrosine 1.80nM/mg ± 0.39. Ovariectomized rats showed liver phenylalanine 3.07nM/mg ± 1.14; liver tyrosine 2.63nM/mg ± 1.01; kidney phenylalanine 2.30 nM/mg ± 0.74; kidney tyrosine 1.93nM/mg ± 0.63. Ovariectomized and estradiol supplemented rats presented with liver phenylalanine 2.84nM/mg ± 1.40; liver tyrosine 2.35nM/mg ± 1.28; kidney phenylalanine 1.91nM/mg ± 0.26, kidney tyrosine 1.67nM/mg ± 0.23.). When, however, the phenylalanine/tyrosine ratio in the liver was evaluated, ovariectomized rats showed a significant decrease of the quotient (p = 0.001). The phenylalanine/tyrosine ratio was restored by estradiol replacement. Our findings show that phenylalanine and tyrosine metabolism is under estradiol control. The effect on the metabolic changes could be mediated by enzyme systems as phenylalanine hydroxylase, tyrosine hydroxylase and tyrosine aminotransferase. Our results would be compatible with previous reports on the stimulatory effect of estradiol on these enzymes. The kidney phenylalanine/tyrosine ratio was unaffected by ovariectomy and/or estradiol replacement which can be easily explained by different pools, enzyme activities, filtration/reabsorption effects, etc.The urinary P/T ratio was decreased by ovariectomy and restored by estradiol replacement indicating endocrine control of renal reabsorption and secretion mechanisms. 相似文献
18.
Barnett YA Eger K Eriksson S Folkers G Hansen PE Hofbauer R Komitowsky D Milon A Munch-Petersen B;European Thymidine Kinase Study Group 《Biotechnology advances》1994,12(4):663-668
A precondition for the chemotherapeutic treatment of a variety of virally-induced human diseases and malignant conditions is a highly selective interaction of the drug molecule to be used with it's biological target. To ensure the development of novel, effective drugs, it is essential that the biological target is well characterised with regard to it's structure and activity. Such characterisation relies upon adequate amounts of pure target being available. One of the most important enzymatic importers for antimetabolites is the enzyme thymidine kinase. In this article an in vitro protein expression system is described which facilitates the production of milligram amounts of pure and biologically active thymidine kinase, from a number of important biological sources. Results have shown that the in vitro produced enzyme has the exact biochemical propeties of the in vivo enzyme. Thus the in vitro protein expression system is an ideal vechicle to facilitate an in depth investigation of the enzyme's biological properties. 相似文献
19.
Gerardo D. Castro Christian J. Stamato Jos A. Castro 《Free radical biology & medicine》1994,16(6):693-701
The interaction between free radicals derived from the catalytic decomposition of carbon tetrachloride and tyrosine (the N-acetyl tyrosine ethyl ester, ATEE) under anaerobic and aerobic conditions was studied. The structure of the reaction products formed was desciphered by the GLC/MS analysis of their trimethylsilyl derivatives. Under anaerobic conditions the formation of the following products was found: (1) an unsaturated derivative of the amino acid; (2) the trimethylsilyl derivative of N-acetyl chloro tyrosine ethyl ester; (3) a hydroxyl adduct of ATEE ; (4) an ATEE adduct having a chlorine and a CCl3 group in the molecule (it is suggested that CCl3 is attached to the benzyl carbon and the chlorine located in the benzene ring); (5) an ATEE adduct having only a CCl3 group tentatively assigned to be located on the benzyl carbon; and (6) and (7) were found to be two isomers of an ATEE having one CCl3 on the aromatic ring. Under aerobic conditions the following reaction products were identified: Two products which were similar to those numbered (1) and (2) and formed anaerobically; (8) and (11) two isomeric dichlorinated adducts of ATEE; (9) and (10) two isomeric dichlorinated monohydroxylated derivatives of ATEE. Concerning the potential relevance of these findings, we consider that if similar interactions to those here reported occurred during CCl4 poisoning, the activity of enzymes having tyrosine in their active center might result in impairment. Further, enzymes operating on tyrosine moieties in proteins might be perturbed in their action if tyrosine groups were attacked by the free radicals arising from catalytic decomposition of CCl4 evidenced here. 相似文献
20.
Giovanna Berruti 《Molecular reproduction and development》1994,38(4):386-392
The majority of cellular responses to changing environmental conditions is regulated by protein kinases. Spermatozoa have many special properties, including motility with demonstrated chemotaxis, the ability to undergo capacitation, and the acrosome reaction, which are in part controlled by extracellular signals and in which sperm kinases are considered to be involved. We have previously reported that there is a protein kinase activity, which phosphorylates the synthetic substrate poly-(Glu, Tyr) with a Km value of 2.3 μM, and is inhibited by the tyrosine kinase inhibitor tyrphostin, in the protein extract from boar spermatozoa (Berruti and Porzio, 1992: Biochim Biophys Acta 1118:149–154). Now we have demonstrated that the enzyme is cytosolic, is active as a monomer of Mr 42,000, is stimulated by Mg2+ > Mn2+ but not by Ca2+, is renaturable, and can phosphorylate native protein substrates such as microtubule-associated protein 2 (MAP2) and histone H2B both on the tyrosine and serine residues. N-terminal sequence analysis suggests that it is a novel protein. These new findings imply that the boar sperm 42 kD kinase may be a novel member of the emerging class of dual-specificity protein kinases, and they raise the intriguing question of its function in the protein kinase network mediating signal transduction in mammalian spermatozoa. © 1994 Wiley-Liss, Inc. 相似文献