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)

Phenylalanine hydroxylase activities in extracts of livers from rats pretreated with glucagon are higher than in controls. This time-dependent activation is seen when the hydroxylase is assayed in the presence of tetrahydrobiopterin, but not in the presence of 2-amino-4-hydroxy-6,7-dimethyltetrahydropterin. A maximum 4-fold stimulation of hydroxylase activity was correlated with a conversion of the multiple forms of the enzyme to a single form. This form is characterized by an increased extent of phosphorylation compared to the unactivated enzyme. Incorporation of radioactive inorganic phosphate into phenylalanine hydroxylase following administration of glucagon was determined after specific immunoprecipitation of the enzyme from partially purified preparations. Sodium dodecyl sulfate disc gel electrophoresis showed that stimulation of enzyme activity is accompanied by incorporation of 32Pi into the protein to the extent of 0.7 mol/mol of hydroxylase subunit. These results demonstrate the phosphorylation of hepatic phenylalanine hydroxylase in vivo and strongly support the idea that the activity of this enzyme can be hormonally regulated through a phosphorylation mechanism.
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PMID:Glucagon stimulation of rat hepatic phenylalanine hydroxylase through phosphorylation in vivo. 69 Jan 16

Induction of diabetes in rats is associated with a significant elevation in the phenylalanine hydroxylating capacity of the liver. This phenomenon reflects an increase in the abundance of both phenylalanine hydroxylase protein and phenylalanine hydroxylase-specific mRNA. These changes can be abolished by insulin-dependent control of diabetes. We show here that the control of diabetes by oral administration of sodium orthovanadate will also nullify the diabetes-related alterations in phenylalanine hydroxylase expression. In addition, diabetes-induced changes in the extent of phosphorylation of phenylalanine hydroxylase are reversed by either insulin or vanadate treatment in vivo. These treatments also abolished the diabetes-related, approx. 30-fold, decrease in glucagon sensitivity of phenylalanine hydroxylation in isolated liver cells.
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PMID:The effect of vanadate upon the expression of phenylalanine hydroxylase in streptozotocin-diabetic rat liver. 138 16

Rats were given intraperitoneal injections of 2 mCi of carrier-free 32Pi and substances known to activate liver phenylalanine hydroxylase. After 30 min, these animals were anesthetized and their livers removed for analysis of enzyme activity, 32Pi incorporation into immunoprecipitated phenylalanine hydroxylase and [gamma-32P]ATP specific activity. Following glucagon treatment, rat liver phenylalanine hydroxylase activity was stimulated more than 6-fold when assayed in the presence of the natural cofactor, tetrahydrobiopterin (BH4). Glucagon injection also resulted in an incorporation of 0.41 mol of 32Pi/mol of hydroxylase subunit (approximately 50,000 Da). In vivo stimulation of phenylalanine hydroxylase activity and 32Pi incorporation by glucagon had been previously observed in this laboratory (Donlon, J., and Kaufman, S. (1978) J. Biol. Chem. 253, 6657-6659). However, we show for the first time in the present study that in vivo treatment with phenylalanine alone results in a 4-fold increase in the BH4-dependent activity of phenylalanine hydroxylase concomitant with a significant incorporation of phosphate into phenylalanine hydroxylase (0.51 mol of 32Pi/mol of hydroxylase subunit). It is further demonstrated in vivo that the combined treatment with phenylalanine and glucagon results in a greater than 10-fold stimulation of BH4-dependent activity and the greatest level of 32Pi incorporation (0.75 mol of 32Pi/mol of hydroxylase subunit). Phenylalanine did not produce an elevation in plasma glucagon in these animals. A model is, thereby, proposed with respect to the ligand binding effects of phenylalanine on the state of phosphorylation and activation of phenylalanine hydroxylase. The significance of these regulatory roles are considered in light of the probable physiological environment of the enzyme.
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PMID:Phenylalanine-induced phosphorylation and activation of rat hepatic phenylalanine hydroxylase in vivo. 173 Jun 77

A monoclonal antibody (PH 7), which recognizes the phosphorylated form of phenylalanine hydroxylase from human liver, has been used for the analysis of the enzyme in crude cell extracts from rat. In immunoblot analyses of rat liver cell extracts, the extent of binding of PH 7 closely correlates with the phosphorylation state of phenylalanine hydroxylase, as judged by [32P]Pi incorporation. These observations have made possible the rapid non-radioactive quantification of hormonal effects on phenylalanine hydroxylase phosphorylation state. In particular, the glucagon-dependent phosphorylation of phenylalanine hydroxylase in liver cells was investigated. Epidermal growth factor was shown to modulate this process. In addition, this technique was used to demonstrate, for the first time, that dibutyryl cyclic AMP, unlike the Ca2+ ionophore A23187, stimulates the phosphorylation of phenylalanine hydroxylase in isolated kidney tubules from rat.
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PMID:Experimental determination of the phosphorylation state of phenylalanine hydroxylase. 230 87

The stimulation of phenylalanine hydroxylation in isolated liver cells by sub-maximally effective concentrations of glucagon (less than 0.1 microM) is antagonized by insulin (0.1 nM-0.1 microM). This phenomenon is a consequence of a decrease in the glucagon-stimulated phosphorylation of phenylalanine hydroxylase from liver cells incubated in the presence of insulin. The impact of insulin on the phosphorylation state and activity of the hydroxylase is mimicked by incubation of liver cells in the presence of orthovanadate (10 microM). A series of cyclic AMP and cyclic GMP analogues enhanced phenylalanine hydroxylation: in each case insulin diminished the stimulation of flux. These results are discussed in the light of the characteristics of insulin action on other metabolic processes.
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PMID:The role of insulin in the modulation of glucagon-dependent control of phenylalanine hydroxylation in isolated liver cells. 303 97

The role of polyamines in the control of phenylalanine hydroxylase phosphorylation state and enzymic activity was investigated. Pre-treatment of liver cells with spermine (1 mM) abolishes the glucagon (1 nM)-stimulated increase in hydroxylase phosphorylation. Concurrently there is a decrease in phenylalanine hydroxylation flux, reflecting decreased enzyme activity; 50% inhibition occurs at approx. 10 microM-spermine. These results are discussed in the context of reports concerning the properties of protein phosphatase 2A.
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PMID:The polyamine-dependent modulation of phenylalanine hydroxylase phosphorylation state and enzymic activity in isolated liver cells. 380 Aug 81

Chronic (10-day) diabetes was associated with increased metabolic flux through phenylalanine hydroxylase in isolated liver cells. This flux was stimulated by 0.1 microM-glucagon, but not by 10 microM-noradrenaline; 0.1 microM-insulin affected neither basal nor glucagon-stimulated flux. The increased rate of phenylalanine hydroxylation in diabetes was accompanied by parallel increases in enzyme activity (as measured with artificial cofactor) and immunoreactive-enzyme-protein content. In contrast with total protein synthesis, which decreased, phenylalanine hydroxylase synthesis persisted at the control rate in cells from diabetic animals. These findings are discussed in relation to the hormonal regulation of the hydroxylase and the known metabolic consequences of chronic diabetes.
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PMID:The effect of experimental diabetes on phenylalanine metabolism in isolated liver cells. 388 93

Hormonal control of the phosphorylation of phenylalanine hydroxylase was studied by using rat liver cells incubated with [32P]Pi. After immunoprecipitation from cell extracts, the hydroxylase was subjected to proteinase digestion and subsequent sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. V8-proteinase digestion yielded one major 32P-labelled fragment, of approx. 9 kDa. Chymotrypsin digestion gave five 32P-labelled fragments ranging from approx. 39 kDa to approx. 10 kDa. Noradrenaline (10 microM) and glucagon (0.1 microM) enhanced the 32P content of all peptide fragments uniformly. Phorbol ester, in contrast with ionophore A23187, did not stimulate enzyme phosphorylation or enhance phenylalanine metabolism in liver cells. These results are discussed in relation to the nature of the protein kinase(s) that mediate phosphorylation of phenylalanine hydroxylase in liver cells.
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PMID:Phosphopeptide analysis of phenylalanine hydroxylase isolated from liver cells exposed to hormonal stimuli. 395 49

Moderate doses of glucagon (20 micrograms/kg I.V.) are sufficient to stimulate rat hepatic phenylalanine hydroxylase in vivo. In addition, the stimulation of the tetrahydrobiopterin-dependent phenylalanine hydroxylase activity in livers of animals fed on a high-protein diet has been correlated with an elevated phosphate content. The tetrahydrobiopterin-dependent hydroxylase activity in these animals can be further elevated by glucagon-stimulated phosphorylation. These results indicate that physiological changes in glucagon concentration modulate rat liver phenylalanine hydroxylase activity in vivo. The current understanding of the role of phosphorylation in regulating human phenylalanine hydroxylase is also considered.
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PMID:Effect of glucagon on hepatic phenylalanine hydroxylase in vivo. 404 62

Glucagon administered subcutaneously to rats for 10 days had no significant effect on liver phenylalanine hydroxylase activity, but induced liver dihydropteridine reductase more than twofold. In rats administered a phenylalanine load orally, glucagon treatment stimulated oxidation and depressed urinary phenylalanine excretion. These responses could not be related to an effect of glucagon on hepatic tyrosine-alpha-oxoglutarate aminotransferase activity. Even in rats with phenylalanine hydroxylase activity depressed to 50% of control values by p-chlorophenylalanine administration, glucagon treatment increased the phenylalanine-oxidation rate substantially. Although hepatic phenylalanine-pyruvate aminotransferase was increased tenfold in glucagon-treated rats, glucagon treatment did not increase urinary excretion of phenylalanine transamination products by rats given a phenylalanine load. Glucagon treatment did not affect phenylalanine uptake by the gut or liver, or the liver content of phenylalanine hydroxylase cofactor. It is suggested that dihydropteridine reductase is the rate-limiting enzyme in phenylalanine degradation in the rat, and that glucagon may regulate the rate of oxidative phenylalanine metabolism in vivo by promoting indirectly the maintenance of the phenylalanine hydroxylase cofactor in its active, reduced state.
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PMID:Effect of glucagon on phenylalanine metabolism and phenylalanine-degrading enzymes in the rat. 415 91


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