Inactivation of phosphorylated rat tyrosine hydroxylase by ascorbate in vitro.

Tyrosine hydroxylase activity is reversibly controlled by the actions of several protein kinases. Previous studies showed that, following phosphorylation by protein kinase A, physiological concentrations of ascorbate irreversibly inactivate tyrosine hydroxylase. Several studies were performed to establish the mechanism of inactivation.

Regulation of tyrosine hydroxylase activity in rat PC12 cells by neuropeptides of the secretin family.

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, is subject to regulation by the cAMP as well as the calcium and cGMP second messenger systems. Treatment of intact rat PC12 cells with neuropeptides including secretin and vasoactive intestinal polypeptide (VIP) stimulated tyrosine hydroxylase activity 2 to 3-fold in vitro. Secretin (EC50 = 10 nM) was about 3 orders of magnitude more potent than VIP (EC50 = 3 microM).

Adenosine receptor activation and the regulation of tyrosine hydroxylase activity in PC12 and PC18 cells.

We compared the response of rat PC12 cells and a derivative PC18 cell line to the effects of adenosine receptor agonists, antagonists, and adenine nucleotide metabolizing enzymes. We found that theophylline (an adenosine receptor antagonist), adenosine deaminase, and AMP deaminase all decreased basal cyclic AMP content and tyrosine hydroxylase activity in the PC12 cells, but not in PC18 cells. Both cell lines responded to the addition of 2-chloroadenosine and 5'-N-ethylcarboxamidoadenosine, adenosine receptor agonists, by exhibiting an increase in tyrosine hydroxylase activity and cyclic AMP content.

Activation of tyrosine hydroxylase in PC12 cells by the cyclic GMP and cyclic AMP second messenger systems.

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, is subject to regulation by a variety of agents. Previous workers have found that cyclic AMP-dependent protein kinase and calcium-stimulated protein kinases activate tyrosine hydroxylase. We wanted to determine whether cyclic GMP might also be involved in the regulation of tyrosine hydroxylase activity.

Degradation of rat brain cholinergic muscarinic receptors in vitro: enhancement by agonists and inhibition by antagonists.

Cholinergic muscarinic receptors undergo proteolytic degradation in vitro under physiological conditions as shown by a loss in [3H]quinuclidinylbenzilate binding activity. The serine protease inhibitor phenylmethylsulfonyl fluoride was very effective in diminishing the receptor loss. Soybean trypsin inhibitor was less effective.

Human brain and placental choline acetyltransferase: purification and properties.

Choline acetyltransferase (EC 2.3.1.