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Biomedical subjects

D M Chuang

Publications and source records attributed to D M Chuang.

At least 145 records · Page 8Linked to original sources
PubMed1980

Down regulation of dihydroalprenolol and imipramine binding sites in brain of rats repeatedly treated with imipramine.

In rats receiving repeated injections of imipramine, there is a reduction in the number of high affinity binding sites for [3H]imipramine and [3H]dihydroalprenolol present in crude synaptic membrane preparations from various brain structures. The location of the sites that become subsensitive to the two ligands did not coincide; the binding sites to [3H]imipramine became subsensitive in the hippocampus but not in cortex or cerebellum. In contrast the binding sites to [3H]dihydroalprenolol became subsensitive in cortex and cerebellum but not in hippocampus. It can be suggested that in rats repeatedly treated with imipramine the down regulation of beta-adrenergic receptors may not coincide with the down regulation of the high affinity binding sites for imipramine. Such a dissociation is supported further by experiments with rats treated with iprinidol.

Alprenolol↗
PubMed1979

Translocation of cytosol protein kinase into nuclei and the induction of tyrosine hydroxylase in NBD-2 neuroblastoma cells.

Exposure of neuroblastoma cells (NBD-2) to 8-bromo-adenosine 3',5'-cyclic monophosphate (0.2-1.0 mM) (8-Br-cAMP) for 15 min caused a long term increase in the Vmax of tyrosine-3-monooxygenase activity (TH) beginning about 1 day after 8-Br-cAMP application. Cyclic AMP-dependent histone kinase was maximally activated in about 30 min and stayed activated above pretreatment levels for one hour. In cells exposed to 8-Br-cAMP for 15 min, separation of soluble and particle bound histone kinase showed that the total histone kinase activity in the soluble fraction decreased by 40%. This decrease was accompanied by an increase in protein kinase activity in the particulate fraction, suggesting enzyme translocation. After translocation, the enzyme appears to acquire a different substrate affinity because it prefers as a PO43- acceptor, acidic protein rather than histone. In NBD-2 cells this kinase appears to precede, and may be related to, the delayed increase in TH Vmax.

Cell Nucleus↗
PubMed1979

beta-Adrenergic receptors of frog erythrocytes. Biochemical sequelae following stimulation with isoproterenol.

Following persistent stimulation of beta-adrenergic receptors of frog erythrocytes with (-)-isoproterenol, the cyclic adenosine 3',5'-monophosphate-dependent protein kinase (cAMP-dependent protein kinase) (EC 2.7.1.37) was activated for several hours. This activation outlasted the duration of the increase of cAMP content. Following a persistant stimulation of beta-adrenergic receptors with isoproterenol, the phosphorylation of selective membrane proteins was increased. This increase in phosphorylation lasted longer than 4 hr but less than 12 hr. Between 2 and 4 hr after receptor stimulation the loss of beta-adrenergic receptor from plasma membrane was maximal, and the phosphorylation of two membrane proteins characterized by molecular weights of 60,000 and 38,000 daltons was selectively enhanced. In addition we found that isolated erythrocytes are capable of synthesizing RNA and polypeptides and that incubation with (-)-isoproterenol indices a long-term delayed increase of the synthesis of erythrocyte proteins. This increase in the synthesis of proteins appears to require new RNA synthesis. Thus the possibility can be entertained that this delayed increase in protein synthesis participates in the new synthesis of receptor and is operative in the termination of beta-adrenergic receptor subsensitivity elicited by a persistent stimulation with (-)-isoproterenol.

Alprenolol↗
PubMed1979

Evidence for internalization of the recognition site of beta-adrenergic receptors during receptor subsensitivity induced by (-)-isoproterenol.

In the supernatant (30,000 x g) of frog erythrocyte homogenates, by using gel filtration we detected a protein that could bind [(3)H]dihydroalprenolol ([(3)H]DHA) with high affinity. This binding was greatly enhanced when the erythrocytes were preincubated with (-)-isoproterenol. After various periods of incubation with (-)-isoproterenol, the extent of the increase in the density of [(3)H]DHA binding sites in the cytosol was paralleled by a proportional decrease in the number of [(3)H]DHA binding sites in the corresponding pellet; both events peaked after 2-3 hr of incubation with (-)-isoproterenol. The K(a) of the (-)-isoproterenol-induced increase in [(3)H]DHA binding in cytosol and the decrease in this binding in the membrane ranged between 60 and 90 nM. The changes in the cytosol and particulate [(3)H]DHA binding sites were independent of RNA and protein synthesis. The increase in cytosol binding elicited by (-)-isoproterenol was blocked by exposure of the cells to (-)-alprenolol which per se failed to change the cytosol binding of [(3)H]DHA. Scatchard analysis revealed that the enhanced [(3)H]DHA binding to cytosol material was due to a 4-fold increase in the B(max) with little or no change in K(d) ( approximately 9 nM). Binding displacement data show that these soluble [(3)H]DHA binding sites resemble the surface membrane recognition sites. Moreover, the ability of various beta-adrenergic agents to increase [(3)H]DHA binding to cytosol after they were incubated with frog erythrocytes paralleled their affinity for membrane-bound beta receptors. These findings support the view that the beta-adrenergic receptor desensitization caused by prolonged exposure to (-)-isoproterenol is due, at least in part, to an internalization of the recognition site of beta-adrenergic receptors.

Alprenolol↗
PubMed1979

Soluble and membrane-bound protein kinases in newborn and mature rat brain.

We studied the developmental changes of soluble and membrane-bound protein kinases (EC 2.7.1.37) in rat brain and found that the elution profiles from a DEAE-cellulose column by NaCl of adenosine-3':5'-monophosphate (cyclic AMP) dependent protein kinase from cytosol were not significantly different in newborn (0.19 M NaCl) vs. mature (0.21 M NaCl). In addition, there was little change in Kd for cyclic AMP binding of newborn and mature soluble enzyme. In contrast, using endogenous protein as the phosphate acceptor, cyclic AMP dependent and calcium-dependent protein kinases from brain synaptic membranes of mature rats were significantly higher than that of newborn rats.

Age Factors↗
PubMed1978

Characterization of protein kinases from adrenal medulla. A study of cytosol and nuclear enzymes.

Since phosphorylation of chromosomal proteins by cyclic AMP-dependent protein kinases (EC 2.7.1.37) enhances template activity of adrenal medulla chromatin (9), we have studied the properties and regulation of protein kinases isolated from chromaffin cell cytosol and nuclei. DEAE-cellulose chromatography revealed three peaks of kinase activity in the nucleus (nPKI, nPKII, nPKIII) and two in the cytosol (cPKI, cPKII). The three nuclear enzymes, as well as cPKII, did not require cyclic AMP to express their catalytic activity. nPKI and nPKIII preferred acidic substrates as PO3-4 acceptors, while nPKII and the cytosol enzymes preferred basic PO3-4 acceptors. Enzyme recombination experiments using protein kinase regulatory subunits from cytosol suggested that cPKII was the catalytic subunit of cPKI. In contrast, the nuclear enzymes were not catalytic subunits of the cyclic AMP-dependent protein kinase in the cytosol (cPKI). Only the cytosol protein kinases could be inhibited by endogenous heat-stable protein kinase inhibitors. The nuclear and cytosol cyclic AMP-independent protein kinases were distinguishable on the basis of their sedimentation constants as well as Mc2+ and Mn2+ requirements.

Adrenal Medulla↗
PubMed1977

Transfer of ADP-ribose from NAD to choleragen: a subunit acts as catalyst and acceptor protein.

Choleragen selectively incorporates 3H from [3H]NAD labeled on the adenosine moiety and not 14C from [14C]NAD labeled on the nicotinamide moiety. This reaction does not require protein in addition to choleragen. Incorporation of isotope does not proceed at 4 degrees, requires dithiothreitol, is stable after extensive washing with cold trichloroacetic acid, and is decreased 80% by boiling in trichloroacetic acid. Studies with the A and B subunits of choleragen show that the A subunit catalyzes ADP-ribosylation and serves as an acceptor protein. The B subunit does not show catalytic or acceptor activity. We conclude that choleragen and its A subunit catalyze the hydrolysis of NAD and the enzymatic transfer of ADP-ribose to the A subunit.

Adenosine Diphosphate Sugars↗
PubMed1976

Enhanced template activity in chromatin from adrenal medulla after phosphorylation of chromosomal proteins.

Translocation of protein kinase to the nucleus had been implicated earlier in the transsynaptic control of gene expression mediated by cholinergic nerves in adrenal medulla. Phosphorylation of chromosomal proteins by adenosine 3',5'-monophosphate-dependent protein kinase and adenosine 3',5'-monophosphate enhances the template activity of chromatin from adrenal medulla. When homologous RNA polymerase II is used the relative activation is greater than that obtained with Escherichia coli RNA polymerase. The substrate for such phosphorylation does not seem to be RNA polymerase II. Phosphorylation of specific acidic protein probably mediates this enhancement of template activity.

Adenosine Triphosphate↗
PubMed1975

Protein kinase activation as an early event in the trans-synaptic induction of tyrosine 3-monooxygenase in adrenal medulla.

An increase of cAMP/cGMP concentration ratio is the earliest stimulus-coupled biochemical change that has been measured in the adrenal medulla during the trans-synaptic induction of tyrosine 3-monooxygenase [EC 1.14.16.2; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating)]. In adrenal medulla of rats receiving reserpine alone (16 mumol/kg intraperitoneally) or reserpine and propranolol (40 mumol/kg intraperitoneally 30 min before reserpine), or exposed to 4 degrees for 4 hr, the extent and duration of the increase of the cAMP/cGMP concentration ratio exceeds the critical value that is required to activate the protein kinases (EC 2.7.1.37; ATP:protein phosphotransferase). Gel filtration experiments indicate that during this activation, the catalytic subunit of the protein kinase (low-molecular-weight enzyme) is released from the holoenzyme. The activation of protein kinase lasts longer than the increase in the cAMP/cGMP concentration ratio and appears to be an obligatory early event that mediates the increase of tyrosine monooxygenase synthesis. The trans-synaptic induction of the monooxygenase in adrenal medulla appears to be due to an increased synthesis of the enzyme;the rate for monooxygenase degradation is proportional to the number of enzyme molecules that are present at various stages of the induction process.

Adrenal Medulla↗