Biomedical subjects

R Roskoski

Publications and source records attributed to R Roskoski.

At least 19 recordsLinked to original sources

PubMed1991

Tyrosine hydroxylase purification from rat PC12 cells.

Tyrosine hydroxylase was purified in high yield from rat PC12 cells. This three-day procedure consisted of differential ammonium sulfate precipitation, anion-exchange chromatography, and heparin-Sepharose affinity chromatography. It yielded an average of 15 mg of purified protein from 100 flasks of PC12 cells, with greater than 40% recovery of tyrosine hydroxylase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielded a single protein band with a molecular weight of approximately 60,000. The protein had a specific activity of 670 nmol/min/mg and had a Km for its reducing cofactor tetrahydrobiopterin of 1.8 mM. The purified protein can be phosphorylated and activated by cyclic AMP-dependent protein kinase.

Ammonium Sulfate↗

PubMed1991

Phosphorylation of rat tyrosine hydroxylase and its model peptides in vitro by cyclic AMP-dependent protein kinase.

The enzyme tyrosine hydroxylase catalyzes the first step in the biosynthesis of dopamine, norepinephrine, and epinephrine. Tyrosine hydroxylase is a substrate for cyclic AMP-dependent protein kinase as well as other protein kinases. We determined the Km and Vmax of rat pheochromocytoma tyrosine hydroxylase for cyclic AMP-dependent protein kinase and obtained values of 136 microM and 7.1 mumol/min/mg of catalytic subunit, respectively. These values were not appreciably affected by the substrates for tyrosine hydroxylase (tyrosine and tetrahydrobiopterin) or by feedback inhibitors (dopamine and norepinephrine). The high Km of tyrosine hydroxylase correlates with the high content of tyrosine hydroxylase in catecholaminergic cells. We also determined the kinetic constants for peptides modeled after actual or potential tyrosine hydroxylase phosphorylation sites. We found that the best substrates for cyclic AMP-dependent protein kinase were those peptides corresponding to serine 40. Tyrosine hydroxylase (36-46), for example, exhibited a Km of 108 microM and a Vmax of 6.93 mumol/min/mg of catalytic subunit. The next best substrate was the peptide corresponding to serine 153. The peptide containing the sequence conforming to serine 19 was a very poor substrate, and that conforming to serine 172 was not phosphorylated to any significant extent. The primary structure of the actual or potential phosphorylation sites is sufficient to explain the substrate behavior of the native enzyme.

Animals↗

PubMed1990

Inactivation of tyrosine hydroxylase by pterin substrates following phosphorylation by cyclic AMP-dependent protein kinase.

We reported previously that, following phosphorylation by cyclic AMP-dependent protein kinase, tyrosine hydroxylase in rat corpus striatal extracts is inactivated in a time-dependent and apparently irreversible fashion. Removal of low molecular weight substances from these extracts by gel filtration attenuates this inactivation. We tried to determine the identity of endogenous metabolites that promote inactivation of tyrosine hydroxylase under our experimental conditions. In the present study, we report that the reducing co-substrate tetrahydrobiopterin and its analogues promoted this irreversible inactivation. The concentration that produced a 50% loss of activity (at 20 min) of the phosphorylated enzyme was 0.7 microM and that for the unphosphorylated enzyme was 420 microM. Using enzyme purified from a rat pheochromocytoma, we found that tyrosine, alpha-methyl-p-tyrosine, and a 3-iodotyrosine protected the phosphorylated enzyme against the inactivation produced by tetrahydrobiopterin. Catecholamines (dopamine, norepinephrine, epinephrine, and some of their analogues) also nullified inactivation. In contrast, the product of the reaction, dihydroxyphenylalanine, failed to attenuate the inactivation process. We performed several studies to ascertain the mechanism of inhibition by tetrahydrobiopterin. We considered the possibility that it formed reactive free radicals that produced inhibition. Free radical scavengers, however, failed to block the inhibition produced by tetrahydrobiopterin. Superoxide dismutase, catalase, and peroxidase also failed to protect tyrosine hydroxylase against inactivation. Moreover, when the experiments were performed under anaerobic conditions, the inactivation process was unaffected. These results suggest that reactive oxygenated species were not required for inactivation by tetrahydrobiopterin.

Animals↗

PubMed1989

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. The latter finding indicates that both cell lines contained an adenosine receptor linked to adenylate cyclase. We found that the addition of dipyridamole, an inhibitor of adenosine uptake, produced an elevation of cyclic AMP and tyrosine hydroxylase activity in both cell lines. Deoxycoformycin, an inhibitor of adenosine deaminase, failed to alter the levels of cyclic AMP or tyrosine hydroxylase activity. This suggests that uptake was the primary inactivating mechanism of adenosine action in these cells. We conclude that both cell types generated adenine nucleotides which activate the adenosine receptor in an autocrine or paracrine fashion. We found that PC12 cells released ATP in a calcium-dependent process in response to activation of the nicotinic receptor. We also measured the rates of degradation of exogenous ATP, ADP, and AMP by PC12 cells. We found that the rates of metabolism of the former two were at least an order of magnitude greater than that of AMP. Any released ATP would be rapidly metabolized to AMP and then more slowly degraded to adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗

PubMed1989

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). A combination of several protease inhibitors failed to enhance the potency of either peptide. Other members of the secretin family including glucagon and peptide histidine isoleucine (PHI) stimulated tyrosine hydroxylase activity to a lesser extent. Somatostatin, which is not homologous to secretin, was ineffective. The maximal response of tyrosine hydroxylase activation to 1 microM secretin occurred within 6-15 sec. Secretin, VIP, and forskolin also enhanced tyrosine hydroxylase activity (3,4-dihydroxyphenylalanine production) in intact cells, as determined by high performance liquid chromatography and electrochemical detection. Secretin, VIP, PHI, and glucagon increased the levels of cAMP in PC12 cells more than 10-fold, as determined by radioimmunoassay. We also demonstrated that cAMP is released from the cells into the incubation medium following secretin treatment. Secretin and VIP treatment also enhanced the activity of cAMP-dependent protein kinase in a concentration-dependent fashion, as measured subsequently in vitro. Based on the greater potency of secretin in comparison with VIP, PHI, and glucagon, we suggest that the PC12 cells contain a secretin-preferring receptor that increases cAMP levels and brings about an activation of tyrosine hydroxylase activity through the stimulation of cAMP-dependent protein kinase.

Adrenal Gland Neoplasms↗

PubMed1988

Inactivation of yeast hexokinase by o-phthalaldehyde: evidence for the presence of a cysteine and a lysine at or near the active site.

Yeast hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1), a homodimer, was rapidly and irreversibly inactivated by o-phthalaldehyde at 25 degrees C (pH 7.3). The reaction followed pseudo-first-order kinetics over a wide range of the inhibitor concentration. The second-order-rate constant for the inactivation of hexokinase was estimated to be 45 M-1.s-1. Hexokinase was protected more by sugar substrates than by nucleoside triphosphates during inactivation by o-phthalaldehyde. Absorption spectrum (lambda max 338 nm), and fluorescence excitation (lambda max 363 nm) and emission (lambda max 403 nm) spectra of the hexokinase-o-phthalaldehyde adduct were consistent with the formation of an isoindole derivative. These results also suggest that sulfhydryl and epsilon-amino functions of the cysteine and lysine residues, respectively, participating in the isoindole formation are about 3 A apart in the native enzyme. About 2 mol of the isoindole per mol of hexokinase dimer were formed following complete loss of the phosphotransferase activity. Chemical modification of hexokinase by iodoacetamide in the presence of mannose resulted in the modification of six sulfhydryl groups per mol of hexokinase with retention of the phosphotransferase activity. Subsequent reaction of the iodoacetamide modified hexokinase with o-phthalaldehyde resulted in complete loss of the phosphotransferase activity with concomitant modification of the remaining two sulfhydryl groups of hexokinase. Chemical modification of hexokinase by iodoacetamide in the absence of mannose resulted in complete inactivation of the enzyme. The iodoacetamide inactivated hexokinase failed to react with o-phthalaldehyde as evidenced by the absence of a fluorescence emission maximum characteristic of the isoindole derivative. The holoenzyme failed to react with [5'-(p-fluorosulfonyl)benzoyl]adenosine. The dissociated hexokinase could be inactivated by [5'-(p-fluorosulfonyl)benzoyl]adenosine; the degree of inactivation paralleled the extent of reaction between o-phthalaldehyde and the nucleotide-analog modified enzyme. Thus, it is concluded that two cysteines and lysines at or near the active site of the hexokinase were involved in reaction with o-phthalaldehyde following complete loss of the phosphotransferase activity. An important finding of this investigation is that the lysines, involved in isoindole formation, located at or near the active site are probably buried.(ABSTRACT TRUNCATED AT 400 WORDS)

Aldehydes↗

PubMed1988

Differential sensitivity of neural and non-neural protein kinase isozymes to cyclic AMP.

Cyclic AMP-dependent protein kinase, which plays a major role in metabolic and genetic regulation, consists of two classes of isozymes denoted as type I and type II. The type II isozyme, moreover, consists of two subclasses denoted as neural and non-neural based upon immunochemical differences between the enzyme isolated from bovine brain and heart, respectively. Whereas the catalytic (C) subunits of these three isozymes are quite similar, all three isozymes differ with respect to their regulatory (R) subunits. In the present report, we have compared the sensitivities to cyclic AMP of the type I and type II isozymes in several tissues from a single species (rat). The sensitivities of the three isozymes to cyclic AMP were type I much greater than non-neural type II greater than neural type II. We suggest that the differences in sensitivity to cyclic AMP of isozymes present in the same cell provides the cell with a dynamic range of responses to the widely varying alterations in cellular cyclic AMP levels produced by regulatory first messengers.

Adenosine Triphosphate↗

PubMed1988

Inactivation of yeast hexokinase by 2-aminothiophenol. Evidence for a 'half-of-the-sites' mechanism.

Yeast hexokinase is a homodimer consisting of two identical subunits. Yeast hexokinase was inactivated by 2-aminothiophenol at 25 degrees C (pH 9.1). The reaction followed pseudo-first-order kinetics until about 70% of the phosphotransferase activity was lost. About 0.65 mol of 2-aminothiophenol/mol of hexokinase was found to be bound after the 70% loss of the enzyme activity. Completely inactivated hexokinase showed a stoichiometry of about 1 mol of 2-aminothiophenol bound/mol of the enzyme. The evidence obtained from kinetic experiments, stoichiometry of the inactivation reaction and fluorescence emission measurements suggested site-site interaction (weak negative co-operativity) during the inactivation reaction. The approximate rate constants for the reversible binding of 2-aminothiophenol to the first subunit (KI) and for the rate of covalent bond formation with only one site occupied (k3) were 150 microM and 0.046 min-1 respectively. The inactivation reaction was pH-dependent. Dithiothreitol, 2-mercaptoethanol and cysteine restored the phosphotransferase activity of the hexokinase after inactivation by 2-aminothiophenol. Sugar substrates protected the enzyme from inactivation more than did the nucleotides. Thus it is concluded that the inactivation of the hexokinase by 2-aminothiophenol was a consequence of a covalent disulphide bond formation between the aminothiol and thiol function at or near the active site of the enzyme. Hexokinase that had been completely inactivated by 2-aminothiophenol reacted with o-phthalaldehyde. Fluorescence emission intensity of the incubation mixture containing 2-aminothiophenol-modified hexokinase and o-phthalaldehyde was one-half of that obtained from an incubation mixture containing hexokinase and o-phthalaldehyde under similar experimental conditions. The intensity and position of the fluorescence emission maximum of the 2-aminothiophenol-modified hexokinase were different from those of the native enzyme, indicating conformational change following modification. Whereas aliphatic aminothiols were completely ineffective, aromatic aminothiols were good inhibitors of the hexokinase. Cyclohexyl mercaptan weakly inhibited the enzyme. Inhibition of the hexokinase by heteroaromatic thiols was dependent on the nature of the heterocyclic ring and position of the thiol-thione equilibrium. The inhibitory function of a thiol is associated with the following structural characteristics: (a) the presence of an aromatic ring, (b) the presence of a free thiol function and (c) the presence of a free amino function in the close proximity of the thiol function.(ABSTRACT TRUNCATED AT 400 WORDS)

Aniline Compounds↗

PubMed1988

Reaction of low molecular weight aminothiols with o-phthalaldehyde.

o-Phthalaldehyde has been recently shown to be a useful reagent for chemical modification of cyclic nucleotide dependent protein kinases, hexokinase, and fructose-1,6-bisphosphatase. It reacts covalently with closely spaced (approximately 3 A) sulfhydryl and epsilon-amino functions of cysteine and lysine residues, respectively, of these enzymes to yield fluorescent isoindole derivatives. We have found the reagent to be equally useful to investigate the degree of reactivity of sulfhydryl and amino functions in substances that do not possess enzymatic activity, e.g., glutathione, homocysteine, and cysteine. The kinetics of the reaction of nonenzymatic aminothiols with o-phthalaldehyde can be followed rapidly and conveniently by continuously monitoring the increase in relative fluorescence of the isoindole derivatives. The fluorescence emission maxima of the o-phthalaldehyde adducts can be used to compute molar transition energies that provide qualitative but useful information concerning the degree of polarity of microenvironment of the sulfhydryl and amino functions participating in isoindole formation. The kinetic and spectral data obtained from the reaction between o-phthalaldehyde and nonenzymatic low molecular weight aminothiols may be helpful in comparing the reactivities of the sulfhydryl and amino functions in enzymes.

Aldehydes↗

PubMed1988

Allosteric nucleotide specificity of phosphorylase kinase: correlation of binding, conformational transitions, and activation. Utilization of lin-benzo-ADP to measure the binding of other nucleoside diphosphates, including the phosphorothioates of ADP.

Recent work has shown that ADP is an allosteric activator of nonphosphorylated phosphorylase kinase from rabbit skeletal muscle (Cheng, A., Fitzgerald, T. J., and Carlson, G. M. (1985) J. Biol. Chem. 260, 2535-2542). The specificity of the allosteric site for nucleoside diphosphates is further investigated in this study. Only purine nucleoside diphosphates are capable of causing allosteric activation, and an amino group at position 2 or 6 of the purine ring is required. Comparisons are made of the abilities of 5'-diphosphate analogs of ADP, including phosphorothioates, to activate, to bind, and to induce in the enzyme's beta subunits conformational changes associated with activation. Binding is measured by competition titrations utilizing fluorescence polarization of lin-benzo-ADP, itself an allosteric activator; and conformational changes are measured by partial proteolysis and chemical cross-linking. When measured at an identical percentage of saturation at the allosteric site, the abilities of ADP analogs to induce conformational changes in the beta subunits parallel their abilities to activate the holoenzyme. An unmodified beta-phosphate of ADP, although not necessary for binding at the allosteric site, is needed to fully drive the activating conformational transition. The activating nucleoside diphosphate appears to be the free species, as opposed to its Mg2+ complex.

Adenosine Diphosphate↗

PubMed1988

Synthetic peptide analogues differentially alter the binding affinities of cyclic nucleotide dependent protein kinases for nucleotide substrates.

Analogues of a synthetic heptapeptide substrate corresponding to the sequence around a phosphorylation site in histone H2B [Glass, D. B. & Krebs, E. G. (1982) J. Biol. Chem. 257, 1196-1200] were used to assess interactions between the peptide substrate and the ATP binding sites of cGMP-dependent protein kinase and the catalytic subunit of cAMP-dependent protein kinase. The affinity of each protein kinase for lin-benzo-ADP was determined in the absence and presence of substrate peptide by fluorescence anisotropy titrations [Bhatnagar, D., Roskoski, R., Jr., Rosendahl, M. S., & Leonard, N. J. (1983) Biochemistry 22, 6310-6317]. The Kd values of cGMP-dependent protein kinase for lin-benzo-ADP in the absence and presence of cGMP were 7.6 and 9.7 microM, respectively. Histone H2B(29-35) (Arg-Lys-Arg-Ser-Arg-Lys-Glu) had no effect on nucleotide affinity in either the absence or presence of cGMP. However, when lysine-34 located two residues after the phosphorylatable serine is replaced with an alanyl residue, the resulting [Ala34]histone H2B(29-35) and its analogue peptides interact with cGMP-dependent protein kinase and/or the nucleotide in a fashion that decreases nucleotide binding affinity approximately 3-fold. This amino acid replacement had previously been shown to cause an increase in Vmax and a decrease in the pH optimum for the phosphotransferase reaction. Replacement of positively charged residues at positions 30 and 31 of the peptide also decreased nucleotide affinity. Other analogues of histone H2B(29-35) failed to affect binding of lin-benzo-ADP to the active site of the cGMP-dependent enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗

PubMed1988

Inactivation of fructose-1,6-bisphosphatase by o-phthalaldehyde.

Rabbit liver fructose-1,6-bisphosphatase, a tetramer of identical subunits was rapidly and irreversibly inactivated by o-phthalaldehyde at 25 degrees C (pH 7.3). The second-order rate constant for the inactivation was 30 M-1s-1. Fructose-1,6-bisphosphatase was completely protected from inactivation by the substrate--fructose-1,6-diphosphate but not by the allosteric effector--adenosine monophosphate. The absorption spectrum (lambda max 337 nm) and, fluorescence excitation (lambda max 360 nm) and fluorescence emission spectra (lambda max 405 nm) were consistent with the formation of an isoindole derivative in the subunit between a cysteine and a lysine residue about 3A apart. About 4 isoindole groups per mol of the bisphosphatase were formed following complete loss of the phosphatase activity. This suggests that the amino acid residues of the biphosphatase participating in reaction with o-phthalaldehyde more likely reside at or near the active site instead of allosteric site. The molar transition energy of fructose-1,6-bisphosphatase--o-phthalaldehyde adduct was estimated 121 kJ/mol and compares favorably with 127 kJ/mol for the synthetic isoindole, 1-[(beta-hydroxyethyl)thio]-2-(beta-hydroxyethyl) isoindole in hexane. It is, thus, concluded that the cysteine and lysine residues participating in isoindole formation in reaction between fructose-1,6-bisphosphatase and o-phthalaldehyde are located in a hydrophobic environment.

Adenosine Monophosphate↗

PubMed1988

Inactivation of tyrosine hydroxylase activity by ascorbate in vitro and in rat PC12 cells.

Tyrosine hydroxylase activity is reversibly modulated by the actions of a number of protein kinases and phosphoprotein phosphatases. A previous report from this laboratory showed that low-molecular-weight substances present in striatal extracts lead to an irreversible loss of tyrosine hydroxylase activity under cyclic AMP-dependent phosphorylation conditions. We report here that ascorbate is one agent that inactivates striatal tyrosine hydroxylase activity with an EC50 of 5.9 microM under phosphorylating conditions. Much higher concentrations (100 mM) fail to inactivate the enzyme under nonphosphorylating conditions. Isoascorbate (EC50, 11 microM) and dehydroascorbate (EC50, 970 microM) also inactivated tyrosine hydroxylase under phosphorylating but not under nonphosphorylating conditions. In contrast, ascorbate sulfate was inactive under phosphorylating conditions at concentrations up to 100 mM. Since the reduced compounds generate several reactive species in the presence of oxygen, the possible protecting effects of catalase, peroxidase, and superoxide dismutase were examined. None of these three enzymes, however, afforded any protection against inactivation. We also examined the effects of ascorbate and its congeners on the activity of tyrosine hydroxylase purified to near homogeneity from a rat pheochromocytoma. This purified enzyme was also inactivated by the same agents that inactivated the impure corpus striatal enzyme. Under conditions in which ascorbate almost completely abolished enzyme activity, we found no indication for significant proteolysis of the purified enzyme as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We also found that pretreatment of PC12 cells in culture for 4 h with 1 mM ascorbate, dehydroascorbate, or isoascorbate (but not ascorbate sulfate) also decreased tyrosine hydroxylase activity 25-50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Gland Neoplasms↗

PubMed1987

Paraoxon-induced decrease in the muscarinic acetylcholine receptor content in rat heart.

The regulation of the rat heart muscarinic acetylcholine receptor by injection of paraoxon (an acetylcholinesterase inhibitor) was characterized. No changes in receptor density in the four cardiac chambers were seen after two days. After three daily injections, however, significant decreases (20-25%) were observed in both atria and ventricles. These changes were associated with a 50% decrease in cardiac acetylcholinesterase activity. We were unable to demonstrate a change in the proportion or value of the apparent KDs for the two previously described affinity states of the receptor for the agonist methacholine. We found that the proportion of the high affinity form of the receptor was greater in atria than in ventricle (70 vs. 55%). Moreover, we also found that acetylcholinesterase activity was greater in the atria than ventricle. Although methacholine will produce down regulation of the muscarinic receptor in the perfused rat heart in 2.5 h (Reinhardt and Roskoski, 1983; J. Pharmacol. Exp. Ther. 226, 135), injection of large doses of methacholine failed to produce any receptor decreases within 6 h in vivo.

Acetylcholinesterase↗

PubMed1987

Phosphorylation of tyrosine hydroxylase by cyclic GMP-dependent protein kinase.

Tyrosine hydroxylase purified from rat pheochromocytoma was phosphorylated and activated by purified cyclic GMP-dependent protein kinase as well as by cyclic AMP-dependent protein kinase catalytic subunit. The extent of activation was correlated with the degree of phosphate incorporated into the enzyme. Comparable stoichiometric ratios (0.6 mol phosphate/mol tyrosine hydroxylase subunit) were obtained at maximal concentrations of either cyclic AMP-dependent or cyclic GMP-dependent protein kinases. The enzymes appeared to mediate the phosphorylation of the same residue based on the observation that incorporation was not increased when both enzymes were present. The major tryptic phosphopeptide obtained from tyrosine hydroxylase phosphorylated by each protein kinase exhibited an identical retention time following HPLC. The purified phosphopeptides also exhibited identical isoelectric points. These data provide support for the notion that the protein kinases are phosphorylating the same residue of tyrosine hydroxylase.

Animals↗

PubMed1987

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. We found that treatment of rat PC12 cells with sodium nitroprusside (an activator of guanylate cyclase), 8-bromocyclic GMP, forskolin (an activator of adenylate cyclase), and 8-bromocyclic AMP all produced an increase in tyrosine hydroxylase activity measured in vitro or an increased conversion of [14C]tyrosine to labeled catecholamine in situ. Sodium nitroprusside also increased the relative synthesis of cyclic GMP in these cells. In the presence of MgATP, both cyclic GMP and cyclic AMP increased tyrosine hydroxylase activity in PC12 cell extracts. The heat-stable cyclic AMP-dependent protein kinase inhibitor failed to attenuate the activation produced in the presence of cyclic GMP. It eliminated the activation produced in the presence of cyclic AMP. Sodium nitroprusside also increased tyrosine hydroxylase activity in vitro in rat corpus striatal synaptosomes and bovine adrenal chromaffin cells. In all cases, the cyclic AMP-dependent activation of tyrosine hydroxylase was greater than that of the cyclic GMP-dependent second messenger system. These results indicate that both cyclic GMP and cyclic AMP and their cognate protein kinases activate tyrosine hydroxylase activity in PC12 cells.

Adrenal Gland Neoplasms↗

PubMed1985

Adenosine cyclic 3',5'-monophosphate dependent protein kinase: fluorescent affinity labeling of the catalytic subunit from bovine skeletal muscle with o-phthalaldehyde.

The catalytic subunit of adenosine cyclic 3',5'-monophosphate dependent protein kinase from bovine skeletal muscle was rapidly inactivated by o-phthalaldehyde at 25 degrees C (pH 7.3). The reaction followed pseudo-first-order kinetics, and the second-order rate constant was 1.1 X 10(2) M-1 s-1. Absorbance and fluorescence spectroscopic data were consistent with the formation of an isoindole derivative (1 mol/mol of enzyme). The reaction between the catalytic subunit and o-phthalaldehyde was not reversed by the addition of reagents containing free primary amino and sulfhydryl functions following inactivation. The reaction, however, could be arrested at any stage during its progress by the addition of an excess of cysteine or less efficiently by homocysteine or glutathione. The catalytic subunit was protected from inactivation by the presence of the substrates magnesium adenosine triphosphate and an acceptor serine peptide substrate. The decrease in fluorescence emission intensity of incubation mixtures containing iodoacetamide- or 5'-[p-(fluorosulfonyl)benzoyl]adenosine-modified catalytic subunit and o-phthalaldehyde paralleled the loss of phosphotransferase activity. Catalytic subunit denatured with urea failed to react with o-phthalaldehyde. Inactivation of the catalytic subunit by o-phthalaldehyde is probably due to the concomitant modification of lysine-72 and cysteine-199. The proximal distance between the epsilon-amino function of the lysine and the sulfhydryl group of the cysteine residues involved in isoindole formation in the native enzyme is estimated to be approximately 3 A. The molar transition energy of the catalytic subunit-o-phthalaldehyde adduct was 121 kJ/mol and compares favorably with a value of 127 kJ/mol for the 1-[(beta-hydroxyethyl)thio]-2-(beta-hydroxyethyl)isoindole in hexane, indicating that the active site lysine and cysteine residues involved in formation of the isoindole derivative of the catalytic subunit are located in a hydrophobic environment. o-Phthalaldehyde probably acts as an active site specific reagent for the catalytic subunit.

Affinity Labels↗

PubMed1985

Inactivation of guanosine cyclic 3',5'-monophosphate dependent protein kinase from bovine lung by o-phthalaldehyde.

Guanosine cyclic 3',5'-monophosphate (cGMP) dependent protein kinase is inactivated by o-phthalaldehyde. The loss of phosphotransferase activity following treatment with o-phthalaldehyde was rapid, and the second-order rate constant at 25 degrees C and pH 7.3 was 35 M-1 s-1. The inactivation reaction did not follow saturation kinetics. The cGMP-dependent protein kinase was protected from inactivation by its substrates, MgATP and Ser-peptide. Fluorescence excitation and emission spectroscopic data showed that an isoindole derivative was formed following the reaction between cGMP-dependent protein kinase and o-phthalaldehyde. Four moles of isoindole per mole of the cGMP-dependent protein kinase dimer was formed following complete inactivation by o-phthalaldehyde. In the absence of cGMP, the protein kinase lost only 50% of its cGMP binding activity while there was almost a complete loss of its phosphotransferase activity. Studies in the presence of 20 microM cGMP, however, showed that about 2 mol of isoindole groups per mole of the protein kinase dimer was formed following complete inactivation by o-phthalaldehyde. The second-order rate constant for inactivation of cGMP-dependent protein kinase by o-phthalaldehyde in the presence of 20 microM cGMP was 40 M-1 s-1. Fluorescence measurements of samples containing inactivated, iodoacetamide-modified, or 5'-[p-(fluorosulfonyl)benzoyl]adenosine-modified, cGMP-dependent protein kinase and o-phthalaldehyde showed that the intensity of fluorescence in each case was about 50% of that obtained from unmodified, active cGMP-dependent protein kinase and o-phthalaldehyde.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldehydes↗