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1.
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
2.
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
3.
Insulin stimulation of nucleoside triphosphatase activity in isolated nuclear envelopes 总被引：8，自引：0，他引：8
The activity of nucleoside triphosphatase, an enzyme that regulates nuclear messenger RNA transport, was measured in highly purified nuclear envelopes isolated from rat liver. Addition of picomolar concentrations of insulin to freshly prepared nuclear envelopes directly increased the enzyme activity. The major effect of insulin on this enzyme was to increase the maximum velocity of its activity; no significant effects were seen on the affinity constant. These studies raise the possibility, therefore, that the nuclear envelope is a site where insulin regulates nuclear functions. 相似文献
4.
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
5.
Two representative anabolicsteroids caused an increase in the uptake of alpha-aminoisobutyric acid-1-C(14) in the levator ani muscle of rats. The distribution ratio between that muscle and the plasma was increased fourfold by the administration of a synthetic anabolic steroid and twofold by administration of testosterone propionate. The determination of this increase may serve as an indicator for the myotrophic effect of anabolic steroids. 相似文献
6.
After incubation at 37 degrees C the subsequent uptake of alpha-aminoisobutyric acid, cycloleucine, glycine, and L-proline by newborn (as compared to adult) rat kidney cortex slices is enhanced. The effect is abolished by the presence of cycloheximide, actinomycin D, and high concentrations of the above-mentioned amino acids in the medium during the 37 degrees C incubation prior to measurement of uptake. The data suggest that there is an adaptive control mechanism which is expressed on incubation at 37 degrees C and which can regulate amino acid transport in newborn rat kidney cortex. 相似文献
7.
Human diabetes associated with a deletion of the tyrosine kinase domain of the insulin receptor 总被引：11，自引：0，他引：11
M Taira M Taira N Hashimoto F Shimada Y Suzuki A Kanatsuka F Nakamura Y Ebina M Tatibana H Makino 《Science (New York, N.Y.)》1989,245(4913):63-66
The insulin receptor has an intrinsic tyrosine kinase activity that is essential for signal transduction. A mutant insulin receptor gene lacking almost the entire kinase domain has been identified in an individual with type A insulin resistance and acanthosis nigricans. Insulin binding to the erythrocytes or cultured fibroblasts from this individual was normal. However receptor autophosphorylation and tyrosine kinase activity toward an exogenous substrate were reduced in partially purified insulin receptors from the proband's lymphocytes that had been transformed by Epstein-Barr virus. The insulin resistance associated with this mutated gene was inherited by the proband from her mother as an apparently autosomal dominant trait. Thus a deletion in one allele of the insulin receptor gene may be at least partly responsible for some instances of insulin-resistant diabetes. 相似文献
8.
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
9.
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
10.
Blood-brain neutral amino acid transport activity is increased after portacaval anastomosis 总被引：21，自引：0，他引：21
In rats after portacaval anastomosis (an animal model of chronic liver disease), transport of tryptophan and other members of the large neutral amino acid group from blood to brain was markedly enhanced. Increased transport activity was apparently restricted to the neutral amino acid transport system, since brain uptake of glucose, inulin, and tyramine was unaffected while blood-brain arginine transport was significantly reduced. These results strikingly confirm the hypothesis that carrier-mediated blood-brain transport is the limiting factor determining the availability of the neutral amino acids to the brain. The encephalopathy associated with cirrhosis may be the result of abnormal neurotransmitter metabolism and neurotransmission secondary to increased neutral amino acid transport activity and an increased brain content of members of the neutral amino acid group. 相似文献
11.
BRONK JR 《Science (New York, N.Y.)》1963,141(3583):816-818
Triiodothyronine administered to thyroidectomized rats preferentially increased the total capacity of the electron transport phosphorylation system when isolated mitochondria from the liver were tested with different substrates, but it caused little increase in the activity of the slowest dehydrogenases and no uncoupling. The increased activity appeared to be partly due to direct activation of some component of the electron transport system, although triiodothyronine injection also stimulated the incorporation of amino acids by isolated mitochondria. 相似文献
12.
Homogenates of HeLa cells contain neuraminidase activity. This enzyme is particle-bound, and it has a pH optimum of 4.2. Hydrocortisone-regulated cells contain two to three times as much neuraminidase as the corresponding controls. The hydrocortisone treatment also causes an increase in the cell content of beta-glucuronidase and acid deoxyribonuclease. 相似文献
13.
Ontogeny of soluble and mitochondrial tyrosine aminotransferases 总被引：1，自引：0，他引：1
R D Koler P J Vanbellinghen J H Fellman R T Jones R E Behrman 《Science (New York, N.Y.)》1969,163(873):1348-1350
The development of the soluble and mitochondrial forms of tyrosine aminotransferase was observed in fetal and neonatal rhesus monkey tissues. The mitochondrial activity is detectable in early fetal life; the soluble form reaches significant activity just before the birth of the animal. 相似文献
14.
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
15.
Retinyl acetate: effect on cellular content of RNA in epidermis in cell culture in chemically defined medium 总被引：1，自引：0，他引：1
Cell cultures of epidermis from newborn mice were established in chemically defined medium. Additions of retinyl acetate to these cultures caused a significant increase in cellular RNA content. Addition of insulin and hydrocortisone to the cultures potentiated the effect of retinyl acetate on cellular RNA content. 相似文献
16.
胰岛素是调节糖代谢的重要激素。本试验测定了向空腹绵羊瘤胃灌注混合挥发性脂肪酸和改变灌注混合挥发性脂肪酸的乙：丙酸比例之后,颈动脉血浆胰岛素水平的动态变化。结果表明,向空腹绵羊瘤胃灌注高乙：丙酸比例(75：15)的混合挥发性脂肪酸,胰岛紊水平在开始灌注后3．5h内逐渐上升,但未出现胰岛素分泌高峰。将瘤胃灌注混合挥发性脂肪酸的乙：丙酸比例改换为65：25后,血浆胰岛素水平迅速上升。在27～52min之间维持了较高水平,之后迅速下降,出现胰岛素分泌高峰。进一步提高瘤胃灌注混合挥发性脂肪酸的丙酸比例。使乙：丙酸比例达45：45,未出现胰岛素水平的动态变化。本研究结果说明,瘤胃乙：丙酸比例为75：15时。体内糖代谢调节状态与瘤胃乙：丙酸比例为65：25和45：45时不同。胰岛素对体内糖代谢的调节主要依赖于胰岛素水平在短时间的变化,而不是胰岛素水平的高低。 相似文献
17.
Tryptophan pyrrolase induced in human liver by hydrocortisone: effect on excretion of kynurenine 总被引：2，自引：0，他引：2
Administration of hydrocortisone causes two- to fourfold increase in the level of activity of tryptophan pyrrolase in human liver, as measured in needle-biopsy specimens. Correlation of the higher levels of the enzyme with the amounts of urinary kynurenine suggests that the tryptophan pyrrolase level, which is regulated by adrenocortical hormones, may be the important variable in the increased excretion of tryptophan metabolites that accompanies various diseases. 相似文献
18.
酒精阳性乳牛血清皮质醇含量变化及其与代谢关系的探讨 总被引：1，自引：0，他引：1
本文通过酒精阳性乳牛与阴性乳牛血清中皮质醇，蛋白质及其代谢产物尿素氮，血糖和游离脂酸（ＦＦＡ）的测定，发现在阳性牛血中皮质醇含量的消涨规律的同时，出现阳性牛血糖升高，蛋白质降低，尿素氮升高，ＦＦＡ升高。结果表明，酒精阳性乳牛体内糖，脂质和蛋白质代谢发生了变化。这个变化与皮质醇等激素消涨有直接关系，为研究酒精阳性乳的发生机理提供了可靠的依据。 相似文献
19.
Hormone-dependent differentiation of mammary gland: sequence of action of hormones in relation to cell cycle 总被引：6，自引：0，他引：6
Differentiation of mouse mammary gland in vitro requires insulin, hydrocortisone, and prolactin. The epithelial cells must first divide in order to synthesize casein in response to these hormones. Insulin is required for the initiation of DNA synthesis and is also necessary during G(1) phase (after mitosis). Prolactin can elicit the overt differentiative responses after mitosis. Activity of hydrocortisone precedes that of prolactin, that is, after mitosis it is not capable of eliciting the differentiative response. 相似文献
20.
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