共查询到20条相似文献，搜索用时 31 毫秒
1.
L S Freedman S Samuels I Fish S A Schwartz B Lange M Katz L Morgano 《Science (New York, N.Y.)》1980,207(4433):902-904
Rates of tyrosine and lysine transport and incorporation into protein were measured in control and undernourished weanling rats. Undernutrition was induced by feeding lactating dams a low protein diet (12 percent casein) from birth to day 21. At weaning, body and brain weights of undernourished rats were 50 percent and 88 percent, respectively, of control values. Lysine and tyrosine transport rates into skeletal muscle were reduced by over 75 percent, more than twice the reduction seen in brain. Rates of amino acid incorporation into muscle protein were reduced by approximately 50 percent; the change in rate of incorporation into brain protein was not statistically significant. These data indicate that, in spite of marked retardation of amino acid transport into brain, the brain seems fully capable of maintaining normal rates of protein synthesis. 相似文献
2.
By administering C(14)-la-beled tyrosine or H(3)-labeled 3,4-dihy-droxyphenylalanine to guinea pigs it has been possible to achieve sufficient labeling of the norepinephrine and dopamine in the brain to permit measurement of their turnover rates. The half-life of brain dopamine was about 2.5 hours. The half-life of norepinephrine was about 4 hours, suggesting a rate of synthesis of at least 0.03 to 0.04, microg/g per hr or 2.4 microg/day for the whole guinea pig brain. 相似文献
3.
L-Dopa methyl ester: prolongation of survival of neuroblastoma-bearing mice after treatment 总被引：1，自引：0，他引：1
M M Wick 《Science (New York, N.Y.)》1978,199(4330):775-776
L-Dopa has has been shown to demonstrate enhanced toxicity toward melanoma cells in vitro. Since melanocytes arise from the neural crest embryologically, the effect of L-dopa methyl ester, a soluble analog, on the murine C1300 neuroblastoma was studied. There was significant antitumor activity against the neuroblastoma, which was enhanced by combination with a dopa decarboxylase inhibitor, Ro4-4602. In vitro studies suggested inhibition of DNA synthesis as the principal site of action. A mechanism involving sulfhydryl compound scavenging is postulated. 相似文献
4.
Dihydroxyphenylalanine in rat food containing wheat and oats 总被引：4，自引：0，他引：4
Dopa has been identified in rat food by three different fluorimetric assays and paper chromatography. Incubation of the rat food with proteolytic enzymes dramatically increased the measurable free dopa. Analysis of samples of six individual protein-containing constituents of rat food revealed that both wheat and oats contain dopa. 相似文献
5.
The fouling marine mussel Mytilus edulis attaches itself to various substrates by spinning byssal threads, the adhesive discs of which are rich in the amino acid 3,4-dihydroxyphenylalanine (dopa). An acid-soluble protein was extracted and purified from the phenol gland located in the byssus-secreting foot of the animal. This protein is highly basic and contains large amounts of lysine, dopa, and 3- and 4-hydroxyproline. The composition of this protein and its sticky tendencies in vitro strongly suggest that it contributes to byssal adhesion. 相似文献
6.
Estradiol is concentrated in tyrosine hydroxylase-containing neurons of the hypothalamus 总被引：9，自引：0，他引：9
M Sar 《Science (New York, N.Y.)》1984,223(4639):938-940
Localization of [3H]estradiol in tyrosine hydroxylase-containing neurons of rat brain was shown by a combined technique of autoradiography and immunohistochemistry. [3H]Estradiol was concentrated in the nuclei of tyrosine hydroxylase-containing neurons in the nucleus arcuatus, nucleus periventricularis hypothalami, and the zona incerta. These results suggest that estradiol acts directly on dopamine-producing neurons of the tuberoinfundibular system and incertohypothalamic system. 相似文献
7.
Eumelanins and pheomelanins: characterization by electron spin resonance spectroscopy 总被引：3，自引：0，他引：3
Synthetic dopa melanin and cysteinyldopa melanin have different electron spin resonance spectra. Data are reported for mixtures of these melanins and for dopa-cysteinyldopa copolymers, which are spectroscopically similar. A simple parameterization of the spectra allows estimation of the relative amounts of (i) dopa melanin and cysteinyldopa melanin in mixtures and of (ii) dopa and cysteinyldopa incorporated into copolymers. Several natural eumelanins and pheomelanins have been characterized and shown to be copolymers. 相似文献
8.
It was recently reported that cycloheximide, an inhibitor of protein synthesis, induces tyrosine transaminase in the liver of adrenalectomized rats. We have been unable to confirm this effect in the anesthetized animal and our data show that cycloheximide inhibits the induction caused by hydrocortisone in adrenalectomized rats or by stress in intact rats. 相似文献
9.
The purine analog azaguanine does not inhibit the initial induction of hepatic tyrosine transaminase by hydrocortisone. However, the continued induced synthesis of tyrosine transaminase, elicited by repeated doses of hydro-cortisone, is inhibited approximately 64 percent in the presence of the analog after 7 to 8 hours and appears to be almost completely inhibited by 9 to 10 hours; this suggests that the induction cycle involves the activation and renewal of a pool of preexisting messenger RNA. 相似文献
10.
When plasma tryptophan is elevated by the injection of tryptophan or insulin, or by the consumption of carbohydrates, brain tryptophan and serotonin also rise; however, when even larger elevations of plasma tryptophan are produced by the ingestion of protein-containing diets, brain tryptophan and serotonin do not change. The main determinant of brain tryptophan and serotonin concentrations does not appear to be plasma tryptophan alone, but the ratio of this amino acid to other plasma neutral amino acids (that is, tyrosine, phenylalanine, leucine, isoleucine, and valine) that compete with it for uptake into the brain. 相似文献
11.
Preference for ethyl alcohol was significantly reduced or totally abolished in rats given orally p-chlorophenylalanine, a tryptophan hydroxylase inhibitor that selectively depletes brain serotonin. Some aversion to alcohol was observed while p-chlorophenylalanine was administered, but the rats' rejection of alcohol was even more marked after the drug was discontinued. Oral administration of alpha-methyl-p-tyrosine, a tyrosine hydroxylase inhibitor that depletes brain catecholamines, slightly reduced selection of alcohol, but preference returned to normal as soon as alpha-methyl-p-tyrosine was terminated. 相似文献
12.
Turnover of rat liver tyrosine transaminase: stabilization after inhibition of protein synthesis 总被引：39，自引：0，他引：39
F T Kenney 《Science (New York, N.Y.)》1967,156(774):525-528
Turnover of the rat liver tyrosine transaminase in vivo was measured by a label and chase procedure under conditions where the amount of enzyme undergoes no change. Half-life of the (14)C-labeled enzyme in this basal condition was found to be 1.5 +/- 0.3 hours. Inhibitors of protein synthesis (cycloheximide or puromycin) do not appreciably influence the basal enzyme level over a 5-hour period, although these drugs will block hormonal induction of this enzyme. In pulse-labeling experiments, cycloheximide blocked transaminase synthesis almost completely. The conclusion that enzyme degradation, as well as synthesis, must be blocked when protein synthesis is stopped was confirmed in experiments showing that labeled enzyme is stable in the liver of rats treated with cycloheximide The participation of a continuously synthesized polypeptide in the degradative phase of transaminase turnover is suggested. 相似文献
13.
Tyrosine aminotransferase: enzyme induction independent of adenosine 3', 5'-monophosphate 总被引：12，自引：0，他引：12
The importance of adenyl cyclase and adenosine 3',5'-monophosphate in the induction of tyrosine aminotransferase by adrenocorticosteroids has been tested in HTC cells derived from a rat hepatoma and grown in tissue culture. Adrenocorticosteroids cause a 10-to 15-fold increase in the rate of synthesis of tyrosine aminotransferase in these cells. Under various experimental conditions, with or without glucocorticoids, neither adenyl cyclase nor cyclic adenosine mono-phosphate could be detected in HTC cells. In addition, neither the cyclic nucleotide nor N(6), O(2')-dibutyryl cyclic adenosine monophosphate caused increased activity of the transaminase in HTC cells. We conclude that induction of tyrosine aminotransferase by glucocorticoids is not mediated by the adenyl cyclase-cyclic adenosine monophosphate system. 相似文献
14.
Electroshock effects on brain protein synthesis: relation to brain seizures and retrograde amnesia 总被引：5，自引：0，他引：5
The effects of electroshock on brain seizure activity and brain protein synthesis were studied in male mice. A significant but short-lasting inhibition of brain protein synthesis and an increase in the amount of free leucine were produced by electroshock at intensities above the brain seizure threshold. Electroshock at intensities below the brain seizure threshold did not affect brain protein synthesis. 相似文献
15.
The drug, 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP), depletes striatal dopamine levels in primates and certain rodents, including mice, and produces parkinsonian-like symptoms in humans and nonhuman primates. To investigate the consequences of grafting adrenal medullary tissue into the brain of a rodent model of Parkinson's disease, a piece of adult mouse adrenal medulla was grafted unilaterally into mouse striatum 1 week after MPTP treatment. This MPTP treatment resulted in the virtual disappearance of tyrosine hydroxylase-immunoreactive fibers and severely depleted striatal dopamine levels. At 2, 4, and 6 weeks after grafting, dense tyrosine hydroxylase-immunoreactive fibers were observed in the grafted striatum, while only sparse fibers were seen in the contralateral striatum. In all cases, tyrosine hydroxylase-immunoreactive fibers appeared to be from the host rather than from the grafts, which survived poorly. These observations suggest that, in mice, adrenal medullary grafts exert a neurotrophic action in the host brain to enhance recovery of dopaminergic neurons. This effect may be relevant to the symptomatic recovery in Parkinson's disease patients who have received adrenal medullary grafts. 相似文献
16.
通过动物药理试验，发现儿茶素能明显减少兔外伤皮损内Ｄｏｐａ阳性的黑色细胞数，从而减少局部的色素沉着．试验结果表明，儿茶素治疗色素沉着主要是通过调节机体自由基系统，保护ＳＯＤ活性，抑制酪氨酸酶的活性，从而抑制ＬＰＯ的形成，减少含酪氨酸酶的黑素细胞，从而达到减轻色素沉着的效果． 相似文献
17.
为探索花青素生物合成的调控机制,以模式植物拟南芥野生型Col–0和酪氨酸降解途径缺陷突变体sscd1为试验材料,分析5种浓度(0、0.1、0.5、1.0、2.0mmol/L)外源苯丙氨酸处理后花青素的积累和花青素生物合成相关基因的表达,探讨酪氨酸降解途径受阻是否影响苯丙氨酸诱导花青素的积累。结果发现:外源添加不同浓度苯丙氨酸能提高拟南芥幼苗花青素的含量,而且花青素的含量随着苯丙氨酸浓度的增加而增多;苯丙氨酸处理后,sscd1突变体幼苗中花青素的积累增多,同时花青素生物合成基因,如PAL、CHI、CHS、DFR、LDOX、UF3GT的表达水平在sscd1突变体中都显著上调,表明SSCD1基因突变会阻断酸酪氨酸降解,增加苯丙氨酸诱导花青素的合成。 相似文献
18.
Tolerance to morphine-induced increases in [14C]catecholamine synthesis in mouse brain 总被引：1，自引：0，他引：1
C B Smith J E Villarreal J H Bednarczyk M I Sheldon 《Science (New York, N.Y.)》1970,170(962):1106-1108
Morphine sulfate increased the incorporation of carbon-14-labeled tyrosine into labeled catecholamines in the mouse brain. Tolerance was manifested by a shift to the right in the dose-response curve for morphine after mice were treated repeatedly with morphine. Naloxone, a specific morphine antagonist, also shifted the dose-response curve for morphine to the right. 相似文献
19.
Effect of phospholipase C-gamma overexpression on PDGF-induced second messengers and mitogenesis 总被引：24，自引：0，他引：24
B Margolis A Zilberstein C Franks S Felder S Kremer A Ullrich S G Rhee K Skorecki J Schlessinger 《Science (New York, N.Y.)》1990,248(4955):607-610
Platelet-derived growth factor (PDGF) stimulates phospholipase C (PLC) activity and the phosphorylation of the gamma isozyme of PLC (PLC-gamma) in vitro and in living cells. The role of PLC-gamma in the phosphoinositide signaling pathway was addressed by examining the effect of overexpression of PLC-gamma on cellular responses to PDGF. Overexpression of PLC-gamma correlated with PDGF-induced tyrosine phosphorylation of PLC-gamma and with PDGF-induced breakdown of phosphatidylinositol 4,5-bisphosphate (PIP2). However, neither bradykinin- nor lysophosphatidic acid-induced phosphoinositide metabolism was enhanced in the transfected cells, suggesting that the G protein-coupled phosphoinositide responses to these ligands are mediated by other PLC isozymes. The enhanced PDGF-induced generation of inositol trisphosphate (IP3) did not enhance intracellular calcium signaling or influence PDGF-induced DNA synthesis. Thus, enzymes other than PLC-gamma may limit PDGF-induced calcium signaling and DNA synthesis. Alternatively, PDGF-induced calcium signaling and DNA synthesis may use biochemical pathways other than phosphoinositide metabolism for signal transduction. 相似文献
20.
Brains of rats undernourished from midgestation and killed at weaning contained 25 percent less norepinephrine than brains of adequately fed littermates. Perinatal undernutrition also suppressed the accumulation of brain dopamine. Paradoxically, the activity of tyrosine hydroxylase, the enzyme thought to be rate-limiting in catecholamine biosynthesis, was significantly increased in brains from undernourished animals. 相似文献