Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.14.16.2 (tyrosine hydroxylase)
 14,760 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanisms of tyrosine hydroxylase (TH) activation by depolarization or exposure of dopaminergic terminals to cyclic AMP have been compared using rat striatal slices. Tissues were incubated with veratridine or 60 mM K+ (depolarizing conditions), on the one hand, and forskolin or dibutyryl cyclic AMP, on the other. K+-(or veratridine-)induced depolarization triggered an activation of TH (+75%) that persisted in soluble extracts of incubated tissues. This effect disappeared when drugs (EGTA, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, Gallopamil) preventing Ca2+- and calmodulin-dependent processes were included in the incubating medium. In contrast, prior in vivo reserpine treatment or in vitro addition of benztropine did not affect the depolarization-induced activation of TH. In vitro studies of soluble TH extracted from depolarized tissues indicated that activation was associated with a marked increase in the enzyme Vmax but with no change in its apparent affinity for the pteridin cofactor 6-methyl-5,6,7,8-tetrahydropterin (6-MPH4) or tyrosine. Furthermore, the activated enzyme from depolarized tissues exhibited the same optimal pH (5.8) as native TH extracted from control striatal slices. In contrast, TH activation resulting from tissue incubation in the presence of forskolin or dibutyryl cyclic AMP was associated with a selective increase in the apparent affinity for 6-MPH4 and a shift in the optimal pH from 5.8 to 7.0-7.2. Clear distinction between the two activating processes was further confirmed by the facts that heparin- and cyclic AMP-dependent phosphorylation stimulated TH activity from K+-exposed (and control) tissues but not that from striatal slices incubated with forskolin (or dibutyryl cyclic AMP). In contrast, the latter enzyme but not that from depolarized tissues could be activated by Ca2+-dependent phosphorylation. These data strongly support the concept that Ca2+- but not cyclic AMP-dependent phosphorylation is responsible for TH activation in depolarized dopaminergic terminals.
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PMID:Characteristics of tyrosine hydroxylase activation by K+-induced depolarization and/or forskolin in rat striatal slices. 286 Feb 7

Purification of rat striatal tyrosine hydroxylase in the presence of protease inhibitors effected a high yield of apparently homogeneous enzyme which is stable to prolonged storage. The purified enzyme migrates as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a molecular weight of 61,300. Removal of protease inhibitors results in the appearance of additional bands with molecular weights of 59,800 and 57,000. Cyclic AMP-dependent protein kinase incorporates 1 mol of phosphate/61,000-Da subunit of tyrosine hydroxylase, and concomitantly decreases the apparent Km of the enzyme for cofactor. Phosphorylated tyrosine hydroxylase is unstable at 37 degrees C, exhibiting a 50% decrease in apparent Vmax in 40 min with no change in Km for cofactor. Levels of incorporated phosphate remain constant over this time period. Tyrosine hydroxylase activated by and in the presence of phosphatidylinositol or high concentrations of NaCl exhibited a similar loss of activity at 37 degrees C, whereas enzyme activated by heparin was relatively stable. The rate of phosphorylation of tyrosine hydroxylase is markedly increased in the presence of any of these effectors, suggesting that they promote a common conformation. Further, heparin appears to bind to tyrosine hydroxylase at a site distant from the phosphorylation site. Physiological effectors of tyrosine hydroxylase may act in concert with cyclic AMP-dependent phosphorylation, perhaps by binding to an allosteric site, to regulate enzyme activity in vivo.
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PMID:Purification and characterization of rat striatal tyrosine hydroxylase. Comparison of the activation by cyclic AMP-dependent phosphorylation and by other effectors. 286 Dec 3

To determine if both the Ca2+-calmodulin system and the cyclic AMP system may regulate tyrosine hydroxylase (TH) activity in situ, rat striatal tissue slices that contain all of the components of the TH, cyclic AMP and Ca2+-calmodulin systems were subjected to experimental manipulations. Incubation of striatal tissue slices in a medium containing W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide], a specific inhibitor of calmodulin, resulted in a dose-dependent decrease of DOPA formation. The concentration of W-7 producing 50% inhibition (3 X 10(-5)M) of DOPA formation was in good agreement with the binding affinity of W-7 to calmodulin. W-7 did not affect TH activity in vitro or cellular cyclic AMP level. A structurally unrelated calmodulin antagonist, trifluoroperazine, also inhibited DOPA formation. On the other hand, incubation of striatal tissue slices in a medium containing dibutyryl cyclic AMP (DBcAMP) increased DOPA formation dose dependently. Kinetic analysis revealed that the enzyme in homogenates of control tissue slices had two different Km values for a cofactor, 6-methyl-5,6,7,8-tetrahydropterin (6MPH4), indicating the presence of two forms in striatal tissue slices: a less active form with a relatively low affinity for the pterin cofactor and a more active form with a relatively high affinity. W-7 produced an increase of the high Km form and a decrease of the low Km form respectively. In contrast, incubation of tissue slices in the presence of DBcAMP resulted in almost complete activation of the enzyme to the low Km form. These results suggest that both the Ca2+-calmodulin-dependent system and the cyclic AMP-dependent system may regulate TH activity in the rat striatum in vivo. The different types of kinetic change produced by DBcAMP and W-7 indicate that the two processes may act in different fashions and that the basal level of catechol formation in striatal tissue slices may be dependent upon an activated form of TH.
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PMID:Evidence for the involvement of Ca2+-calmodulin and cyclic AMP in the regulation of the tyrosine hydroxylase system in rat striatal tissue slices. 286 20

Subjecting either P2 fraction or purified synaptosomes isolated from rat brain to periods of anoxic incubation at 30 degrees resulted in activation of dopamine synthesis from tyrosine. This activation was approximately 2.5-fold when the anoxic incubation was carried out at pH 6.2 but was not significant when the pH was 7.4. Measurements of the tyrosine hydroxylase activity at pH 6.2 in Triton X-100-treated preparations of the P2 fraction showed that, after 20 min of anaerobiosis, the Km for pterine cofactor decreased by 39% and the Ki for dopamine increased by 44%; there was no change in the Km for tyrosine. Half-maximal activation of dopamine synthesis occurred in 10 min of anaerobic incubation, and the reversal upon addition of oxygen had a half-time of 15 min. Addition of forskolin or dibutyryl cyclic AMP to anaerobic incubations of P2 fraction did not result in significant activation of dopamine synthesis. Either the removal of calcium or the addition of calmodulin inhibitor, trifluoperazine, substantially decreased the activation of dopamine synthesis induced by periods of anaerobiosis. It appears that during anoxic incubation tyrosine hydroxylase underwent an activation which occurred over a period of minutes, was stable to detergent treatment, and was fully reversed over a period of minutes following reoxygenation. This activation was, at least in part, dependent on the presence of calcium and was sensitive to the calmodulin antagonist trifluoperazine.
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PMID:Activation of tyrosine hydroxylase in the central nervous system by anaerobiosis. 286 73

Subtotal destruction of central noradrenergic neurons with the neurotoxin, 6-hydroxydopamine, is known to increase tyrosine hydroxylase (TH) activity within surviving nerve terminals. The present report demonstrates a similar, dose-related elevation of TH activity in the adrenal medulla and sympathetic nerves after systemic 6-hydroxydopamine treatment. Two temporally distinct processes were observed in the sympathetic nerves: a rapid activation of TH, present during the first few days after the lesion, and a more gradual increase in maximal TH activity, most probably due to enzyme induction. In this regard, the stimulatory effect on catecholamine biosynthesis of cyclic AMP-dependent phosphorylation was attenuated substantially within cardiac sympathetic nerves 3 days after the lesion, but by 3 weeks the efficacy of cyclic AMP-dependent phosphorylation was restored completely. Similarly, the normal activation of cardiac TH activity elicited by insulin-induced hypoglycemia and cold stress was absent soon after 6-hydroxydopamine treatment, but returned 3 weeks later. These latter findings suggest that the adaptations within the sympathoadrenal system after subtotal sympathectomy can preclude further adaptations to stress.
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PMID:Tyrosine hydroxylase activity in the sympathoadrenal system under basal and stressful conditions: effect of 6-hydroxydopamine. 286 49

The possible control of tyrosine hydroxylase (TH) activity by dopaminergic receptor-dependent mechanisms was investigated using rat striatal slices or synaptosomes incubated in the presence of various 3,4-dihydroxyphenylethylamine (dopamine or DA) agonists and antagonists. Under "normal" conditions (4.8 mM K+ in the incubating medium), the DA agonists apomorphine, 6,7-dihydroxy-N,N-dimethyl-2-aminotetralin (TL-99), 7-hydroxy-N,N-dipropyl-2-aminotetralin (7-OH-DPAT), Trans-(-)-4,4a,5,6,7,8,8a,9-octahydro-5-propyl-2H-pyrazolo-3,4- quinoline, and 3-(3-hydroxyphenyl)-N-n-propylpiperidine decreased TH activity in soluble extracts of incubated tissues. In the case of the catechol-containing drugs apomorphine and TL-99, this effect was partly due to a direct inhibition of the enzyme, but in all other cases it appeared to depend on the stimulation of presynaptic DA autoreceptors. No effect of DA antagonists was detected on TH activity under "normal" conditions. In contrast, when tissues were incubated in a K+ -enriched (60 mM) medium, (-)-sulpiride and other DA antagonists enhanced TH activation due to depolarization whereas DA agonists were ineffective. Because (-)-sulpiride also increased the enzyme activity in striatal slices exposed to drugs inducing release of DA, such as veratridine and d-amphetamine, it is concluded that the stimulating effect of the DA antagonist resulted in fact from the blockade of the negative control of TH normally triggered by endogenous DA acting on presynaptic autoreceptors. In contrast to TH activation due to K+ -induced depolarization, the activation evoked by tissue incubation with dibutyryl cyclic AMP was unaffected by the typical agonist 7-OH-DPAT or the antagonist (-)-sulpiride. This would suggest that TH control via presynaptic DA autoreceptors normally concerns possible modulations of the cyclic AMP-dependent phosphorylation of the enzyme.
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PMID:Presynaptic dopamine autoreceptors control tyrosine hydroxylase activation in depolarized striatal dopaminergic terminals. 286 32

Phorbol 12,13-dibutyrate (PDBu) increased the production of 3,4-dihydroxyphenylalanine (DOPA) in the superior cervical ganglion of the rat. This effect occurred without a detectable lag and persisted for at least 90 min of incubation. The action of PDBu was half-maximal at a concentration of approximately 0.1 microM; at high concentrations, PDBu produced about a twofold increase in DOPA accumulation. PDBu increased DOPA production in decentralized ganglia and in ganglia incubated in a Ca2+-free medium. The action of PDBu was additive with the actions of dimethylphenylpiperazinium, muscarine, and 8-Br-cyclic AMP, all of which also increase DOPA accumulation, and was not inhibited by the cholinergic antagonists hexamethonium (3 mM) and atropine (6 microM). Finally, PDBu did not increase the content of cyclic AMP in the ganglion. Thus, the action of PDBu does not appear to be mediated by the release of neurotransmitters from preganglionic nerve terminals, by the stimulation of cholinergic receptors in the ganglion, or by an increase in ganglionic cyclic AMP. PDBu also increased the incorporation of 32Pi into tyrosine hydroxylase. PDBu activates protein kinase C, which in turn may phosphorylate tyrosine hydroxylase and increase the rate of DOPA synthesis in the ganglion.
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PMID:Phorbol 12,13-dibutyrate increases tyrosine hydroxylase activity in the superior cervical ganglion of the rat. 286 24

Incubation of rat pheochromocytoma PC12 cells with dibutyryl cyclic AMP or 56 mM K+ is associated with increased activity and enhanced phosphorylation of tyrosine hydroxylase in situ. Following incubation of the PC12 cells with 32Pi, rapid isolation of the tyrosine hydroxylase, and tryptic digestion of the enzyme, two distinct 32P-peptides can be identified after paper electrophoresis. 56 mM K+ increases 32Pi incorporation into both of these peptides, whereas dibutyryl cyclic AMP increases 32Pi incorporation into only one of these peptides. The rate of increase in the incorporation of 32Pi into these two peptides in cells treated with 56 mM K+ is similar. The phosphorylation of tyrosine hydroxylase in PC12 cells occurs exclusively on serine residues. These results suggest that tyrosine hydroxylase in PC12 cells is phosphorylated on serine residues at two or more distinct sites after 56 mM K+ -induced depolarization. Since only one of these sites is phosphorylated by cyclic AMP-dependent protein kinase, activation of tyrosine hydroxylase by 56 mM K+ may involve phosphorylation by multiple protein kinases in rat pheochromocytoma PC12 cells.
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PMID:Enhanced phosphorylation of tyrosine hydroxylase at more than one site is induced by 56 mM K+ in rat pheochromocytoma PC12 cells in culture. 286 28

We have identified a 56-kilodalton protein in cultured bovine adrenal chromaffin cells that is phosphorylated when catecholamine secretion is stimulated. Immunodetection on Western blots from both one- and two-dimensional polyacrylamide gels indicated that this protein was tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis. Two-dimensional polyacrylamide gel electrophoresis of proteins from unstimulated cells revealed small amounts of phosphorylated protein with a molecular weight of 56K and pI values of 6.37 and 6.27 which were subunits of tyrosine hydroxylase. Nicotinic stimulation of chromaffin cells caused the phosphorylation of three proteins of 56 kilodaltons with pI values of approximately 6.37, 6.27, and 6.15 which were tyrosine hydroxylase. The immunochemical analysis also revealed that there was unphosphorylated tyrosine hydroxylase 56 kilodaltons with a pI of 6.5 which may have decreased on nicotinic stimulation. The phosphorylation of tyrosine hydroxylase was associated with an increase in in situ conversion of [3H]tyrosine to [3H]dihydroxyphenylalanine ([3H]DOPA). Muscarinic stimulation also caused phosphorylation of tyrosine hydroxylase, but to a smaller extent than did nicotinic stimulation. The secretagogues, elevated K+ and Ba2+, stimulated phosphorylation of tyrosine hydroxylase and [3H]DOPA production. The effects of nicotinic stimulation and elevated K+ on tyrosine hydroxylase phosphorylation and [3H]DOPA production were Ca2+-dependent. Nicotinic agonists also raised cyclic AMP levels in chromaffin cells after 2 min. Dibutyryl cyclic AMP and forskolin, which have little effect on catecholamine secretion, also caused phosphorylation of tyrosine hydroxylase. These stimulators of cyclic AMP-dependent processes caused the appearance of two phosphorylated subunits of tyrosine hydroxylase with pI values of 6.37 and 6.27. There was also a small amount of phosphorylated subunit with a pI of 6.15. Both agents stimulated [3H]DOPA production. The experiments indicate that tyrosine hydroxylase is phosphorylated and activated when chromaffin cells are stimulated to secrete. The data suggest that the earliest phosphorylation of tyrosine hydroxylase induced by a nicotinic agonist occurs through stimulation of a Ca2+-dependent protein kinase. After 2 min phosphorylation by a cyclic AMP-dependent protein kinase may also occur. Phosphorylation of tyrosine hydroxylase is associated with an increase in in situ tyrosine hydroxylase activity.
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PMID:Cholinergic receptor-mediated phosphorylation and activation of tyrosine hydroxylase in cultured bovine adrenal chromaffin cells. 286 29

Selective modification of the tetrahydrobiopterin levels in cultured chromaffin cells were followed by changes in the rate of tyrosine hydroxylation. Addition of sepiapterin, an intermediate on the salvage pathway for tetrahydrobiopterin synthesis, rapidly increased intracellular levels of tetrahydrobiopterin and elevated the rate of tyrosine hydroxylation in the intact cell. Tyrosine hydroxylation was also enhanced when tetrahydrobiopterin was directly added to the incubation medium of intact cells. When the cultured chromaffin cells were treated for 72 h with N-acetylserotonin, an inhibitor of sepiapterin reductase, tetrahydrobiopterin content and the rate of tyrosine hydroxylation were decreased. Addition of sepiapterin or N-acetylserotonin had no consistent effect on total extractable tyrosine hydroxylase activity or on catecholamine content in the cultured chromaffin cells. Three-day treatment of chromaffin cell cultures with compounds that increase levels of cyclic AMP (forskolin, cholera toxin, theophylline, dibutyryl- and 8-bromo cyclic AMP) increased total extractable tyrosine hydroxylase activity and GTP-cyclohydrolase, the rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin. Tetrahydrobiopterin levels and intact cell tyrosine hydroxylation were markedly increased after 8-bromo cyclic AMP. The increase in GTP-cyclohydrolase and tetrahydrobiopterin induced by 8-bromo cyclic AMP was blocked by the protein synthesis inhibitor cycloheximide. Agents that deplete cellular catecholamines (reserpine, tetrabenazine, and brocresine) increased both total tyrosine hydroxylase and GTP-cyclohydrolase activities, although treating the cultures with reserpine or tetrabenazine resulted in no change in cellular levels of cyclic AMP. Brocresine and tetrabenazine increased tetrahydrobiopterin levels, but the addition of reserpine to the cultures decreased catecholamine and tetrahydrobiopterin content and resulted in a decreased rate of intact cell tyrosine hydroxylation in spite of the increased activity of the total extractable enzyme. These data indicate that in cultured chromaffin cells GTP-cyclohydrolase activity like tyrosine hydroxylase activity is regulated by both cyclic AMP-dependent and cyclic AMP-independent mechanisms and that the intracellular level of tetrahydrobiopterin is one of the many factors that control the rate of tyrosine hydroxylation.
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PMID:Regulation of guanosine triphosphate cyclohydrolase and tetrahydrobiopterin levels and the role of the cofactor in tyrosine hydroxylation in primary cultures of adrenomedullary chromaffin cells. 286 7


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