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1.
The dietary induction of serine dehydrase, produced by the oral intubation of hydrolyzed casein to protein-depleted rats, is markedly inhibited by doses of gamma-radiation of 400 roentgens or higher provided the irradiation is given within an hour after the initial dose of casein. If the irradiation is delayed until 7 hours after the initial dose of casein, induction is not inhibited. In contrast, the cortisone induction of tyrosine alpha-ketoglutarate transaminase is not inhibited by doses of gamma-radiation up to 3200 roentgens; in some instances hormonal induction of this enzyme appears to be enhanced by irradiation. 相似文献
2.
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
3.
Glucagon selectively potentiates an effect of hydrocortisone: when injected into adrenalectoinized rats it increases fourfold the induction by hydrocortisone of tyrosine transaminase, but not of tryptophan pyrrolase. Glucagon alone doubles the basal level of tyrosine transaminase and decreases that of tryptophan pyrrolase. The effects of glucagon on both enzymes resemble those of starvation. 相似文献
4.
Maturation of a stress-activated mechanism inhibiting induction of tyrosine transaminase 总被引：2，自引：0，他引：2
Rats of various ages were subjected to the stress of 30 minutes on a noisy reciprocating shaker 4 hours before their liver tyrosine transaminase and tryptophan pyrrolase activities were measured. Adrenalectomized infants and adults and hypophysectomized adults were also stressed. Intact, stressed infants exhibited an increase in tyrosine transaminase activity, while intact, stressed adults showed no change. In the stressed adrenalectomized adult, tyrosine transaminase activity markedly decreased, while adrenalectomized infants showed no change. Hypophysectomy largely, but not completely, abolished inhibition in the adults. Tryptophan pyrrolase activity, when present, was increased by stress in all age groups, but the increase was abolished by adrenalectomy and hypophysectomy. The results suggest stress-activation of a pituitary mechanism that inhibits or represses activation of tyrosine transaminase and that may not function during early postnatal life. 相似文献
5.
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
6.
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
7.
A cell line derived from normal, adult rat liver has been established; the cells are similar to hepatocytes, as shown by electron microscopy. The addition of dexamethasone to the culture medium induced a three- to sixfold increase in the specific activity of tyrosine alpha-ketoglutarate transaminase; this increase was inhibited by the simultaneous addition of cycloheximide or actinomycin D. The latter, when added to cells given prior treatment with dexamethasone, further enhanced the transaminase activity. Contact-inhibited cells showed a lower response to dexamethasone than exponentially growing cells. 相似文献
8.
Various lectins were found to induce tyrosine aminotransferase in H-35 rat hepatoma cells grown in monolayer culture. Wheat germ agglutinin gave a maximal induction of tyrosine aminotransferase 6 hours after its addition. The induction time course was similar to that elicited by insulin. Fourteen micrograms of wheat germ agglutinin per milliliter gave half-maximal enzyme induction and 50 micrograms per milliliter gave the maximal response. The induction of tyrosine aminotransferase by wheat germ agglutinin was additive with the induction by either dexamethasone or dibutyryl adenosine 3',5'-monophosphate, but was not additive with the tyrosine amino transferase induction by insulin. Wheat germ agglutinin also mimicked insulin in the inhibition of cellular protein degradation in the absence of serum. The insulin-like effects of lectins should be considered in lectin-mediated manipulations such as agglutination. 相似文献
9.
Tyrosine-alpha-ketoglutarate transaminase: induction by epinephrine and adenosine-3',5'-cyclic phosphate 总被引：9，自引：0，他引：9
W D Wicks 《Science (New York, N.Y.)》1968,160(831):997-998
Epinephrine and the N6-O2'-dibutyryl analog of adenosine-3', 5'-cyclic phosphate both are effective inducers of tyrosine-alpha-ketoglutarate transaminase in explants of fetal rat liver maintained in organ culture. Combinations of these inducers with each other and with hydrocortisone, another inducer, yielded results which suggest that cyclic adenylic acid is an intermediate in the induction by epinephrine and that the mechanism by which it induces is different from that by which hydrocortisone operates. 相似文献
10.
The dual control by substrate and hormone of the level of a third adaptive enzyme in animals is described. Injections of hydrocortisone or the substrate tryptophan increased the level of the liver tryptophan-alpha-ketoglutarate transaminase of intact rats within 5 hours. In adrenalectomized rats this enzyme level was increased by hydrocortisone alone, but substrate induction could be demonstrated only if these animals were treated at the same time with hydrocortisone. 相似文献
11.
Tyrosine alpha ketoglutarate transaminase, which is rapidly induced by various agents, shows circadian rhythmicity in the intact rat. This rhythmicity is only slightly altered after adrenalectomy, indicating that adrenal hormones do not play a major role in the metabolic control of the activity of tyrosine alpha ketoglutarate transaminase. On the other hand, phenylalaninepyruvate transaminase, which is not inducible over the same time period, does not show circadian variation. The results suggest that the sensitivity of an enzyme's regulating system to inducing agents may be related to the inherent circadian rhythm of the enzyme. 相似文献
12.
烬灰吸水链霉菌突变体的诱导研究 总被引：1，自引：0，他引：1
烬灰吸水链霉菌对稻瘟病菌、西瓜枯萎病菌等真菌病害均具有不同程度的抑制作用。用物理诱变、化学诱变、复合诱变3种方式对菌株孢子进行处理,最高变异率分别为25·2%,22·2%,24·1%。实验结果表明,物理诱变和复合诱变对菌株孢子有较好的诱变作用,而化学诱变效果不明显。诱变处理时间分别为30s和2min,可诱变产生较多的变异菌株。分别以2%诱变剂诱变处理1·5h以及60s诱变处理筛选的变异菌株对稻瘟病和西瓜枯萎病都有很好的抑制作用。 相似文献
13.
Reformation of functional liver polyribosomes from ribosome monomers in the absence of RNA synthesis 总被引：2，自引：0，他引：2
The administration to rats of the ethyl analog of methionine, ethionine, results in the rapid decrease in the hepatic concentration of adenosine triphosphate followed by an extensive disaggregation of polysomes to ribosome monomers and a concomitant inhibition of protein synthesis. These effects are readily reversed by the injection of methionine or precursors of adenine nucleotides such as adenine. The reformation of liver polyribosomes in such animals following the administration of adenine plus methionine was found to occur under conditions in which new RNA synthesis was markedly inhibited. Free messenger RNA without attached ribosomes must be capable of remaining functionally active in the liver cytoplasm for many hours. 相似文献
14.
15.
Administration of adenosine 3',5'-monophosphate with theophylline produced testosterone-like induction of hexokinase, phosphofructokinase, pyruvate kinase, and glucose-6-phosphate dehydrogenase in the seminal vesicles of both orchidectomized and immature rats. The N(6)-O(2)'-dibutyryl analog of this cyclic nucleotide produced greater increases in vesicular enzyme activities than those induced by the parent compound. The observed enhancement of the key glycolytic enzymes and of hexose monophosphate shunt dehydrogenase was significantly inhibited by actinomycin D and cycloheximide. The evidence indicates that cyclic adenosine monophosphate may be involved as an intermediary in the action of androgenic hormones on male accessory sex organs. 相似文献
16.
PDGF-induced activation of phospholipase C is not required for induction of DNA synthesis 总被引：14，自引：0，他引：14
T D Hill N M Dean L J Mordan A F Lau M Y Kanemitsu A L Boynton 《Science (New York, N.Y.)》1990,248(4963):1660-1663
Platelet-derived growth factor (PDGF) induction of DNA synthesis is believed to involve activation of phospholipase C (PLC) and subsequent accumulation of inositol 1,4,5-triphosphate [I(1,4,5)P3], increase in intracellular Ca2+, activation of protein kinase C (PKC), and receptor down regulation. Generation of these events is triggered by the tyrosine protein kinase (TPK) activity of the PDGF receptor. The TPK inhibitor genistein blocked PDGF induction of these events, including DNA synthesis, with the exception of receptor down regulation. PDGF-induced phosphotyrosine phosphorylations, including receptor autophosphorylation, were inhibited by genistein. Removal of genistein and PDGF resulted in DNA synthesis without the occurrence of PLC activation. These findings indicate that these early events, with the exception of receptor down regulation, are not necessary for PDGF-induced DNA synthesis. 相似文献
17.
The action of an enzyme essential for tryptophan biosynthesis is inhibited by tryptophan and also by an analog of tryptophan. Similarly, histidine and one of its analogs inhibit the action of an enzyme essential for histidine biosynthesis. A mutant resistant to the histidine analog produces an apparently altered enzyme which is insensitive to both the analog and histidine. 相似文献
18.
[目的]探讨2-十三烷酮、槲皮素和单宁酸3种植物次生物质与杨扇舟蛾谷胱甘肽S-转移酶(GSTs)的关系。[方法]用0.01、0.10和1.00 mg/ml浓度的2-十三烷酮、槲皮素和单宁酸处理的杨树叶子分别饲养杨扇舟蛾幼虫,测定喂饲后72 h内杨扇舟蛾虫体GSTs的活性。[结果]低浓度的2-十三烷酮和槲皮素对杨扇舟蛾体内GSTs活性有抑制作用,且随着浓度升高,杨扇舟蛾体内GSTs活性又略有回升,具有一定的诱导作用;而单宁酸的浓度越大,杨扇舟蛾体内GSTs活性越低,不存在诱导作用。[结论]为杨扇舟蛾的有效防治提供了参考。 相似文献
19.
High-resolution nuclear magnetic resonance spectra of selectively deuterated staphylococcal nuclease 总被引：4，自引：0，他引：4
An analog of staphylococcal nuclease has been prepared in which all amino acids, except the six following, are fully deuterated: tryptophan; methionine; tyrosine, in ring positions 2 and 6; histidine, in ring position 2; aspartic acid and asparagine, beta-methylene; and glutamic acid and glutamine, gamma-methylene. The analog has a much simpler high-resolution nuclear magnetic resonance spectrum than the fully protonated enzyme. The effects of calcium ion and of the inhibitor 3', 5'-thymidine diphosphate on the spectrum of the analog were readily detected. 相似文献
20.
Topical application of juvenile hormone analog induces soldier development in the ant Pheidole bicarinata. Soldier induction takes place if the juvenile hormone analog is present during a period of sensitivity that occurs during the last larval instar. Control of worker dimorphism seems to be accomplished through control of timing of metamorphosis. The smallest size at which metamorphosis can be initiated is shifted upwardfrom 1.2 to 1.7 millimeters by exposure to the juvenile hormone analog during the sensitive period. 相似文献