Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of lowering the liver pyridoxal phosphate (PLP) concentration by vitamin B-6 deficiency on the stability of several rat liver enzymes were examined. Three PLP-dependent enzymes (serine dehydratase, ornithine-delta-aminotransferase, and tyrosine aminotransferase) and two non-PLP-dependent enzymes (glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxykinase) were induced in vitamin B-6 deficient and control rats by feeding them high-protein diets or by injecting them with glucagon or dexamethasone. The decline of each activity was followed after withdrawal of the inducer. Serine dehydratase activity declined more rapidly in vitamin B-6 deficient than in control liver; however, ornithine aminotransferase and tyrosine aminotransferase activities were equally stable in deficient and control liver. Ornithine aminotransferase was predominantly in holoenzyme form in both control and deficient rats, whereas tyrosine aminotransferase was predominantly in apoenzyme form in both groups. The proportion of serine dehydratase in apoenzyme was less stable than the holoenzyme. Activity changes of glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxykinase in control and vitamin B-6 deficient rats were similar. The results suggest that differences in the stability of PLP-dependent enzymes in vitamin B-6 deficient rats depend upon differences in the proportions of these enzymes existing as holo- and apoenzyme.
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PMID:Stability of some pyridoxal phosphate-dependent enzymes in vitamin B-6 deficient rats. 0 99

Induction of delta-aminolevulinic acid synthetase by allylisopropylacetamide in organ-cultured chick embryo liver was not appreciably influenced by any of cycli AMP, dibutyryl cyclic AMP, theophylline, glucose, insulin, glucagon, epinephrine, isoproterenol, and hydrocortisone, whereas the activity of tyrosine aminotransferase significantly increased in response to cyclic AMP and some of those hormones. Accumulation of delta-aminolevulinic acid synthetase in the cultured liver cytosol fraction was not appreciably increased by the addition of dibutyryl cyclic AMP or insulin to the incubation medium. Apparently the behaviors of the induction of delta-aminolevulinic acid synthetase in chick embryo liver in ovo and in vitro differ from those in the livers of adult chicken and rat. High concentrations of chloramphenicol suppressed significantly the allylisopropylacetamide-induced increase of delta-aminolevulinic acid synthetase as well as incorporation of 14C-leucine into proteins. The activity of tyrosine aminotransferase, however, was rather increased when relatively low concentrations of chloramphenicol were added to the medium.
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PMID:Comparative studies of the effects of cyclic AMP, various hormones and chloramphenicol on the induction of delta-aminolevulinic acid synthetase and tyrosine aminotransferase in the organ-cultured chick embryo liver. 1 73

A transient rise in cyclic guanosine 3' : 5' monophosphate (c-GMP) in the liver was observed in rats in vivo 10--20 min after partial hepatectomy. A similar increase in c-GMP in the liver was also found in rats in vivo 15 min after infusion of TGH solution (a mixture of triiodothyronine, glucagon, and heparin). In both cases, inductions of ornithine decarboxylase [EC 4.1.1.17] and tyrosine aminotransferase [EC 2.6.1.5] were found 4 hr after the beginning of the experiments. Later, 22 hr after the surgical intervention or hormone infusion, thymidine kinase [EC 2.7.1.21] was activated and liver slices were able to incorporate [3H]thymidine into DNA. These biochemical phenomena were observed commonly in regenerating liver as well as in the liver of rats infused with TGH solution. c-GMP, but not c-AMP, could induce ornithine decarboxylase and tyrosine aminotransferase in isolated, perfused liver.
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PMID:Involvement of cyclic GMP in the initial stage of hepatocytes proliferation. 1 43

The effectiveness of dietary and hormonal treatments in inducing several pyridoxal phosphate-(PLP)-dependent enzymes has been examined in vitamin B-6 deficient rats. Holo- and apoenzymes of serine dehydratase and ornithine aminotransferase were inducible in both control and deficient rats by feeding them 80% casein diets or by injecting them with glucagon. Holo- and apotyrosine aminotransferase were induced in both control and deficient rats by injecting them with glucagon or with dexamethasone phosphate. Phosphoenolpyruvate carboxykinase, a non-PLP-dependent enzyme, was inducible in both control and deficient rats by glucagon treatment if the rats were fed, but not if they had been starved. The degree of induction of certain enzymes depended upon whether rats were fed ad libitum, starved overnight, or fed a protein-free diet prior to the induction period. Phosphoenolpyruvate carboxykinase activities were about the same in both control and deficient rats. In vitamin B-6 deficient rats, both uninduced and induced activities of serine dehydratase, ornithine aminotransferase, and tyrosine aminotransferase assayed in the prsence of PLP, but not in its absence, either equaled or exceeded control values under most experimental conditions. Synthesis of excess of apoenzyme of PLP-dependent enzymes generally accounted for the high total enzyme activity in deficient rats. Differences between values for control and deficient rats could not be accounted for by differences in liver cyclic AMP concentrations nor were they apparently related to reduced food intake of the deficient rats. High apoenzyme concentration during depletion of coenzyme would tend to prevent depletion of active enzyme.
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PMID:Induction of pyridoxal phosphate-dependent enzymes in vitamin B-6 deficient rats. 1 69

In alloxan diabetic rats a stimulatory effect of stress on the activity of liver phosphoenolpyruvate carboxykinase seems to be very likely. In intact animals the inhibitory effect of glucose feeding (15% glucose instead of laboratory diet and water) on the activity of liver tyrosine aminotransferase (TAT) and tryptophan pyrrolase was reconfirmed. Moreover, a reversal of this effect by immobilization for 2.5 h was observed. After a mean intake of 5.3 g glucose/100 g body weight during 16 h this reversal was only partial and after 3.4 glucose/100 g during the same time the glucose effect was abolished. Stimulation of both enzymes by corticosterone and of TAT by stress-induced release of glucagon may play a role in this reversal.
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PMID:Inhibitory effect of immobilization stress on depression of liver tyrosine aminotransferase and tryptophan pyrrolase by glucose feeding in rats. 1 21

1. A factor, which amplifies the inductions of several liver enzymes by glucocorticoid, was partially purified from Proteus mirabilis from rat intestine. The factor (amplifier) was completely inactivated by alpha-glucosidase, but not by other glycoside hydrolases, proteases, nucleases or phosphatases tested; it was also hydrolysed by HCl with liberation of reducing sugars. Thus the oligosaccharide in this factor seems to be essential for the amplification. 2. In adrenalectomized rats the amplifier increased the inductions of several liver enzymes, such as tyrosine aminotransferase and leucine aminotransferase, by glucocorticoid. But it did not amplify the induction of tyrosine aminotransferase by glucagon or insulin or the activities of enzymes that are not induced by glucocorticoid. The amplifier by itself did not have any glucocorticoid-like action in adrenalectomized rat. These results show that the amplifier specifically increases the inductions of liver enzymes by glucocorticoid. 3. Since similar amplification was also observed in isolated perfused liver and cultured hepatoma cells in vitro, the amplifier seems to act directly on the target organ or cells.
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PMID:A new factor from enteric bacteria of rats amplifying induction of liver enzyme by glucocorticoid. 1. Purification, properties and biological action. 2 Oct 83

Tyrosine aminotransferase mRNA was quantitated by translation in a cell-free system derived from wheat germ followed by specific immunoprecipitation of the newly synthesized enzyme subunit. Hepatic poly(A)-containg RNA prepared from rats treated for 4 h with N6, O2'-dibutyryl cyclic AMP and theophylline was approximately 5.6 times more active in directing the synthesis of the tyrosine aminotransferase subunit relative to untreated controls. The overall template activity of the RNA prepared from control and cyclic AMP-treated animals was virtually identical, demonstrating that the cyclic nucleotide effect was specific for the tyrosine aminotransferase mRNA. At all times, after a single injection of dibutyryl cyclic AMP and theophylline, the increase in hepatic enzyme activity was accompanied by corresponding induction in the level of functional tyrosine aminotransferase mRNA. Other inducers of tyrosine aminotransferase, such as glucagon and hydrocortisone, also increased the level of tyrosine aminotransferase mRNA in proportion to their effect on enzyme activity. The RNA polymerase II inhibitor, alpha-amanitin, completely blocked the dibutyryl cyclic AMP-mediated increase in tyrosine aminotransferase mRNA activity. These studies demonstrate that, in intact animals, the induction of tyrosine aminotransferase activity by dibutyryl cyclic AMP can be completely accounted for by a corresponding increase in the level of functional mRNA coding for the enzyme.
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PMID:Increase in hepatic tyrosine aminotransferase mRNA during enzyme induction by N6,O2'-dibutyryl cyclic AMP. 2 49

Adult rat parenchymal hepatocytes can be maintained in primary culture on floating collagen membranes of prolonged periods of time. In this system the enzyme tyrosine aminotransferase is induced by glucagon, (10(-6) to 10(-8) M) hydrocortisone (10(-5) to 10(-8) M), and cyclic adenosine 3':5'-monophosphate (cAMP) (10(-4) to 10(-5) M). Epinephrine (10(-4) M) induces the enzyme only in the presence of hydrocortisone. Addition of actinomycin D inhibited the induction of tyrosine aminotransferase by hydrocortisone and cAMP. Maintenance of the cultured hepatocytes in the presence of glucose (3g/liter) results in partial suppression of the inducing effects of glucagon and cAMP. Cyclic quanosine 3':5'-monophosphate does not mimic the effects of glucose. These results demonstrate that the phenomenon of glucose repression of enzyme induction, demonstrated in vivo in mammalian liver, is independent of changes in levels of serum hormones, which occur in vivo as a result of glucose administration. This study also demonstrates that glucose repression is not mediated by changes in intracellular levels of cAMP and cyclic quanosine 3':5'-monophosphate.
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PMID:Hormonal regulation and the effects of glucose on tyrosine aminotransferase activity in adult rat hepatocytes cultured on floating collagen membranes. 2 9

Factors contributing to modifications in the capability for enzyme adaptation as an expression of aging are reviewed. Specific examples of altered enzyme adaptations during aging include the responses of hepatic glucokinase activity to glucose and hepatic tyrosine aminotransferase activity to starvation in Sprague-Dawley rats. These impaired enzyme adaptations apparently are not the consequence of alterations in hepatic function during aging. Instead, they reflect disturbances in extrahepatic hormonal regulatory mechanisms. Specific examples include modifications in the control of circulating levels of insulin glucagon, corticosteroids, and thyroid hormones. Age-dependent changes in the regulation of circulating levels of insulin probably originate within the impaired ability of pancreatic islets of Langerhans to secrete the hormone in response to glucose. The rationale for exploiting this experimental approach as a means to understand biological aging is discussed.
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PMID:Loss of adaptive mechanisms during aging. 3 73

The regulation of tyrosine aminotransferase activity by glucocorticoids and cyclic AMP was investigated in isolated liver parenchymal cell suspensions. The induction and maintenance of elevated levels of tyrosine aminotransferase activity in liver cells were completely dependent upon the presence of both the synthetic glucocorticoid, dexamethasone, and glucagon of dibutyryl cyclic AMP. No induction was observed when any of these compounds were tested alone. Immunotitration experiments revealed that the 6- to 7-fold increase in tyrosine aminotransferase activity following the addition of dexamethasone and glucagon was accompanied by a parallel increase in the amount of immunologically reactive enzyme protein. Pulse-labeling experiments established that this increase in enzyme protein could be fully accounted for by a corresponding increase in rate of synthesis of tyrosine aminotransferase. Neither hormone had any effect on the rate of degradation of the enzyme. The increase in tyrosine aminotransferase synthesis evoked by the presence of both hormones was blocked by the addition of actinomycin D or cycloheximide to the medium, demonstrating that RNA and protein synthesis were required for the induction of enzyme activity. By varying the time and order of addition of the inducers and inhibitions, evidence was obtained that the hormones act sequentially. The steroid hormone acts first, presumably to increase the level of functional tyrosine aminotransferase mRNA or its precursor. The processing of this precursor to a translatable form or the specific translation of tyrosine aminotransferase mRNA is apparently dependent upon a specific cyclic AMP-controlled process. In vivo experiments demonstrated that both glucocorticoids and cyclic AMP increase the level of functional tyrosine aminotransferase mRNA in the liver. The actions of the steroid hormone and cyclic nucleotide were blocked by alpha amanitin, establishing the requirement for ongoing gene transcription. The protein synthesis inhibitors, cycloheximide, emetine, and puromycin, were as effective as cyclic AMP in increasing tyrosine aminotransferase mRNA activity. The action of these inhibitors is probably related to their ability to elevate hepatic intracellular cyclic AMP levels, thus mimicking cyclic AMP administration. Extension of these in vivo studies to isolated liver cells will provide a valuable system for investigating the regulation of gene expression by glucocorticoids and cyclic AMP.
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PMID:Multihormonal control of tyrosine aminotransferase in isolated liver cells. 4 Jan 15


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