Tyrosine hydroxylase, activity

The dopamine is then concentrated in storage vesicles via an ATP-dependent process. Here the rate-limiting step appears not to be precursor uptake, under normal conditions, but tyrosine hydroxylase activity. This is regulated by protein phosphorylation and by de novo enzyme synthesis. The enzyme requites oxygen, ferrous iron, and tetrahydrobiopterin (BH. The enzymatic conversion of the precursor to the active agent and its subsequent storage in a vesicle are energy-dependent processes. 

Catecholamine biosynthesis begins with the uptake of the amino acid tyrosine into the sympathetic neuronal cytoplasm, and conversion to DOPA by tyrosine hydroxylase. This enzyme is highly localized to the adrenal medulla, sympathetic nerves, and central adrenergic and dopaminergic nerves. Tyrosine hydroxylase activity is subject to feedback inhibition by its products DOPA, NE, and DA, and is the rate-limiting step in catecholamine synthesis the enzyme can be blocked by the competitive inhibitor a-methyl-/)-tyrosine (31). 

Generally the concentration of DA remains remarkably constant irrespective of the level of neuronal activity. One reason for this is that nerve stimulation increases tyrosine hydroxylase activity and DA synthesis. It is thought that tyrosine hydroxylase can exist in two forms with low and high affinities for its tetrahydropteredine co-factor (BEI-4) and that nerve traffic increases the high-affinity fraction. 

Bacopoulus, NG and Bhatnager, RK (1977) Correlation between tyrosine hydroxylase activity and catecholamine concentration or turnover in brain regions. J. Neurochem. 29 631-643. 

Koda, L.Y., and Gibb, J.W. Adrenal and striatal tyrosine hydroxylase activity after methamphetamine. J Pharmacol Exp Ther 185 42-48, 1973. 

The main reason for my suspicion is that in the experiment with AMT where the effeet of methamphetamine on tyrosine hydroxylase activity can be bloeked and then reinstituted by eoadministering /-dopa, one would prediet that if one is really talking about neurotoxie effects, then one ought to be able to observe the same ehanges 2 weeks later. 

Buening, M.E., and Gibb, J.W. Influence of methamphetamine and neuroleptic drugs on tyrosine hydroxylase activity. Eur J Pharmacol 26 30-34, 1974. 

Fibiger, H.C., and McGeer, E.G. Effect of acute and chronic methamphetamine treatment on tyrosine hydroxylase activity in brain and adrenal medulla. Eur J Pharmacol 16 176-180, 1971. 

Graham, D.G. Oxidative pathways for catecholamines in the genesis of neuromelanin and cytotoxic quinones. Mol Pharmacol 14 633-643. 1978. Hotchkiss, A.J., and Gibb, J.W. Long-term effects of multiple doses of methamphetamine on tryptophan hydroxylase and tyrosine hydroxylase activity in rat brain. J Pharmacol Exp Ther 214 257-262, 1980. 

Mandell, A.J., and Morgan, M. Amphetamine-induced increase in tyrosine hydroxylase activity. Nature 227 75-76, 1970. 

Jadhav AL, Ramesh GT. 1997. Pb-induced alterations in tyrosine hydroxylase activity in rat brain. 

Gibb, J.W., Kogan, FJ. Influence of dopamine synthesis on methamphetamine-induced changes in striatal and adrenal tyrosine hydroxylase activity. Naunyn Schmiedeberg s Arch. Pharmacol. 310 185, 1979. 

Kumer SC. Intricate regulation of tyrosine hydroxylase activity and gene expression. J Neurochem 1996 67 443-461. 

Peters, D. A. V., and Tang, S. (1977) The effects of repeated D-lysergic acid diethylamide injections on catecholamine levels and tyrosine hydroxylase activity in rat brain regions. J. Neurochem., 28 59-62. 

Tyrosine hydroxylase (activity of-) ENZ. reaction +0.65 glassy carbon 238... 

Preclinical studies have shown that prenatal exposure to nicotine reduces brain weight, decreases cortical thickness, and produces abnormalities of pyramidal neuron maturation (Lee, 1998). Reduction in CNS markers of catecholamine activity, such as tyrosine hydroxylase activity, have been observed however, these appear to normalize by adolescence (Levitt, 1998). 

The production of dopamine and norepinephrine in your brain begins with the amino acid tyrosine, which is obtained from your diet. Tyrosine is converted to the amino acid levodopa, or L-DOPA, by the en2yme tyrosine hydroxylase. One very important cofactor is iron. Without iron, tyrosine hydroxylase fails to function normally. People with anemia have reduced body levels of iron and, as consequently, may have reduced tyrosine hydroxylase activity and thus reduced production of norepinephrine and dopamine. The decreased brain levels of these important neurotransmitters may lead to a slight depression, although most likely only in people with severe anemia. Generally, in a normal healthy person, the production of these two neurotransmitters is not easily affected by the contents of the diet. 

Muscle-derived differentiation factor (MDF) induces tyrosine hydroxylase expression in a variety of central nervous system neurons, including those of striatum, cerebellum, and cortex. Normally, i.e., without MDF, these neurons do not express this enzyme of catecholamine synthesis. Further in vitro studies revealed that MDF enhances TH-mRNA 40-fold in fetal mesencephalic neurons. In vivo studies, employing infusion of partially isolated MDF, reported this molecule to enhance tyrosine hydroxylase activity in dopamine-depleted striata of 6-OHDA-lesioned animals. Furthermore, an increase of striatal dopamine concentrations and a partial compensation of rotational asymmetry were observed. In contrast, dopaminergic parameters were not affected by administration of MDF in control animals, suggesting that adult dopaminergic neurons may regain sensitivity toward differentiation factors after lesion. 

Stimulation of the presynaptic autoreceptors inhibits tyrosine hydroxylase activity and dopamine synthesis within the dopaminergic nerve terminals in the neostriatum (97-101 however see 102 for a negative report). The effects of dopaminergic drugs which can be ascribed to an action upon the presynaptic autoreceptor include ... 

Activation of neostriatal tyrosine hydroxylase was observed when cyclic AMP was added to high speed supernatants from rat neostriatum (133). Intraventricular injection of dibutyryl cyclic AMP stimulated tyrosine hydroxylation in the neostriatum (134). However, it is still questionable if under physiological conditions this cyclic AMP involvement in the feedback control of tyrosine hydroxylase activity is mediated by presynaptic dopamine receptors or by presynaptic allo-receptors. In addition, if a dopamine sensitive adenylate cyclase is involved in the regulation of neostriatal tyrosine hydroxylase activity it is relevant to know if this adenylate cyclase is linked to a D-1 and/or a D-2 receptor. At this point in time experimental data are not in favour of the presence of a D-l receptor linked to an adeiylate cyclase on the varicosities of dopaminergic neurons in the neostriatum. E.g. concentrations of dopamine agonists stimulating cyclic AMP formation inhibit tyrosine... 

Lindgren N, Xu ZQ, Herrera-Marschitz M, Haycock J, Hokfelt T, Fisone G (2001) Dopamine D(2) receptors regulate tyrosine hydroxylase activity and phosphorylation at Ser40 in rat striatum. Eur J Neurosci 73 773-780. 

Onali P, Olianas MC, Bunse B (1988) Evidence that adenosine A2 and dopamine autoreceptors antagonistically regulate tyrosine hydroxylase activity in rat striatal synaptosomes. Brain Res 456 302-309. 

Arbogast LA, Voogt JL (1995) Hypoprolactinemia decreases tyrosine hydroxylase activity in the tuberoinfund-ibular dopaminergic neurons acutely by protein dephosphorylation and chronically by changes in gene expression. Endocrine 5 801-806. 

Arbogast LA, Voogt JL (1997) Prolactin (PRL) receptors are colocalized in dopaminergic neurons in fetal hypothalamic cell culture elfect of PRL on tyrosine hydroxylase activity. Endocrinology 755 3016-3023. 

Gayrard V, Malpaux B, Tillet Y, Thiery JC (1994) Estradiol increases tyrosine hydroxylase activity of the A15 nucleus dopaminergic neurons during long days in the ewe. Biol Reprod 50 1168-1177. 

Zigmond RE (1988/89) A comparison of the long-term and short-term regulations of tyrosine hydroxylase activity. J Physiol Paris 55 267-271. 

Nakahara D, Hashiguti H, Kaneda N, Sasaoka T, Nagatsu T (1993) Normalization of tyrosine hydroxylase activity in vivo in the striatum of transgenic mice carrying human tyrosine hydroxylase gene—A microdialysis study. Neurosci Lett 158 44-46. 

Robert F, Lambassenas L, Ortemann C, Pujol JF, Renaud B (1993) Microdialysis monitoring of 3,4-dihydroxyphenylalanine accumulation after decarboxylase inhibition—A means of estimate in vivo changes in tyrosine hydroxylase activity of the rat locus ceruleus. J Neurochem 60 721-729. 

Westerink BH, De Vries JB, Duran R (1990) Use of microdialysis for monitoring tyrosine hydroxylase activity in the brain of conscious rats. J Neurochem 54 381 -387. 

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