Comparison of cyclic nucleotide specificity of guanosine 3',5'-monophosphate-dependent protein kinase and adenosine 3',5'-monophosphate-dependent protein kinase.

Guanosine 3',5'-monophosphate-dependent protein kinase (cyclic GMP-dependent protein kinase) and adenosine 3',5'-monophosphate-dependent protein kinase (cyclic AMP-dependent protein kinase) exhibited a high degree of cyclic nucleotide specificity when hormone-sensitive triacylglycerol lipase, phosphorylase kinase, and cardiac troponin were used as substrates. The concentration of cyclic GMP required to activate half-maximally cyclic dependent protein kinase was 1000- to 100-fold less than that of cyclic AMP with these substrates. The opposite was true with cyclic AMP-dependent protein kinase where 1000- to 100-fold less cyclic AMP than cyclic GMP was required for half-maximal enzyme activation. This contrasts with the lower degree of cyclic nucleotide specificity of cyclic GMP-dependent protein kinase of 25-fold when histone H2b was used as a substrate for phosphorylation. Cyclic IMP resembled cyclic AMP in effectiveness in stimulating cyclic GMP-dependent protein kinase but was intermediate between cyclic AMP and cyclic GMP in stimulating cyclic AMP-dependent protein kinase. The effect of cyclic IMP on cyclic GMP-dependent protein kinase was confirmed in studies of autophosphorylation of cyclic GMP-dependent protein kinase where both cyclic AMP and cyclic IMP enhanced autophosphorylation. The high degree of cyclic nucleotide specificity observed suggests that cyclic AMP and cyclic GMP activate only their specific kinase and that crossover to the opposite kinase is unlikely to occur at reported cellular concentrations of cyclic nucleotides.     

Comparison of cyclic nucleotide specificity of guanosine 3′,5′-monophosphate-dependent protein kinase and adenosine 3′,5′-monophosphate-dependent protein kinase

Guanosine 3′,5′-monophosphate-dependent protein kinase (cyclic GMP-dependent protein kinase) and adenosine 3′,5′-monophosphate-dependent protein kinase (cyclic AMP-dependent protein kinase) exhibited a high degree of cyclic nucleotide specificity when hormone-sensitive triacylglycerol lipase, phosphorylase kinase, and cardiac troponin were used as substrates. The concentration of cyclic GMP required to activate half-maximally cyclic dependent protein kinase was 1000- to 100-folds less than that of cylic AMP with these substrates. The opposite was true with cyclic AMP-dependent protein kinase where 1000- to 100-fold less cyclic GMP was required for half-maximal enzyme activation. This contrasts with the lower degree of cyclic nucleotide specificity of cyclic GMP-dependent protein kinase of 25-fold when histone H2b was used as a substrate for phosphorylation. Cyclic IMP resembled cyclic AMP in effectiveness in stimulating cyclic GMP-dependent protein kinase but was intermediate between cyclic AMP and cyclic GMP in stimulating cyclic. AMP-dependent protein kinase. The effect of cyclic IMP on cyclic GMP-dependent protein kinase was confirmed in studies of autophosphorylation of cyclic GMP-dependent protein kinase where both cyclic AMP and cyclic IMP enhanced autophophorylation. The high degree of cyclic nucleotide specificity observed suggests that cyclic AMP and cyclic GMP activate only their specific kinase and that crossover to the opposite kinase is unlikely to occur at reported cellular concentrations of cyclic nucleotides.     

Inactivation of cyclic GMP-dependent protein kinase by N alpha-tosyl-L-lysine chloromethylketone

Cyclic GMP-dependent protein kinase from bovine lung and cyclic AMP-dependent protein kinase from bovine heart are inactivated by N^α-tosyl-L-lysine chloromethylketone (TLCK) in the presence of cyclic GMP and cyclic AMP, respectively. The inactivation of both protein kinases is pseudo-first order, suggesting the rate limiting step is beyond the binding of TLCK. Cyclic GMP-dependent protein kinase is inactivated less than $\text{1}\text{4}$ as rapidly as cyclic AMP-dependent protein kinase, although it shows a higher apparent affinity for TLCK. Cyclic AMP stimulated the rate of inactivation of cyclic AMP-dependent protein kinase 10-fold but cyclic GMP stimulated the rate of inactivation of cyclic GMP-dependent protein kinase only 1.5-fold. The rate of inactivation of cyclic GMP-dependent protein kinase by TLCK is sufficiently rapid (half-time of about 30 min at 37°C with 2 mM TLCK) to account for the effects of TLCK on cell growth observed by others.     

The use of affinity chromatography in purification of cyclic nucleotide receptor proteins.

Biospecific affinity chromatography has been used to purify specific cyclic AMP and cyclic GMP receptor proteins. Several variables are important for successful purification of the cyclic AMP receptor protein, the most critical being the length of the aliphatic spacer side arm. 8-(2-Aminoethyl)-amino-cyclic AMP coupled to the aliphatic spacer side arm. 8-(2-Aminoethyl)-amino-cyclic AMP coupled to agarose specifically retains the cyclic AMP receptor protein by interaction with the immobilized nucleotide. Binding of the cyclic AMP receptor subunit of cyclic AMP-dependent protein kinase to the immobilized nucleotide results in dissociation of the catalytic protein phosphokinase subunit which is not retained. The retained cyclic AMP receptor protein is subsequently eluted by cyclic AMP. Homogeneous cyclic AMP receptor protein prepared from rabbit skeletal muscle by affinity chromatography has been characterized. The molecular weight of the native protein as determined by analytical ultracentrifugation and polyacrylamide gel electrophoresis at varying acrylamide concentrations is 76 800 and 82 000, respectively. The protein is asymmetric with frictional and axial ratios of 1.64 and 12. SDS and urea polyacrylamide gel electrophoresis indicate that the native cyclic AMP receptor is composed of two identical subunits of 42 700 molecular weight. The native protein dimer binds 2 moles of cyclic AMP per mole of protein and is active in suppressing activity of isolated catalytic subunits of cyclic AMP-dependent protein kinase. Cyclic GMP receptor protein from bovine lung has been purified using the same affinity chromatography media. Since cyclic nucleotide binding to cyclic GMP-dependent protein kinase does not result in dissociation of regulatory receptor and catalytic phosphotransferase subunits, the cyclic GMP-dependent protein kinase holoenzyme is retained on the column and can be subsequently specifically eluted with cyclic GMP.     

Photoaffinity labeling of three renal cyclic 3',5'-adenosine monophosphate-binding proteins.

Evidence is presented for the presence of multiple cyclic AMP binding components in the plasma membrane and cytosol fractions of porcine renal cortex and medulla. N6-(Ethyl-2-diazomalonyl)-3',5'-adenosine monophosphate, a photoaffinity label for cyclic AMP binding sites, exhibits non-covalent binding characteristics similar to cyclic AMP in membrane and soluble fractions. Binding data for either compound to the plasma membrane fraction yields biphasic Scatchard plots while triphasic plots are obtained with the dialyzed cytosol. When covalently labeled fractions are separated on SDS-polyacrylamide gel electrophoresis, the cyclic AMP photoaffinity label is found on 49 000 and 130 000 dalton components in each kidney fraction. DEAE-cellulose and gel filtration chromatography of the labeled cortical cytosol fraction establishes that the three components suggested by the binding data correspond to two 49 000 dalton species and a 130 000 component. The 49 000 species have higher affinities for cyclic AMP than the 130 000 component (Ka(1) = 2.0 . 10(9), Ka(2) = 1.7 . 10(8), Ka(3) = 1.0 . 10(7)). The 49 000 components are associated with protein kinase activity while the 130 000 component does not exhibit protein kinase, adenosine deaminase, or cyclic nucleotide phosphodiesterase activity. Immunologic results and effects of phosphorylation and cyclic GMP on cyclic AMP binding further suggest that the 49 000 components are regulatory subunits of cyclic AMP-dependent protein kinases. Cyclic AMP binding to the 130 000 component is markedly inhibited by adenosine and adenine nucleotides, but not cyclic GMP. Thus, this component may reflect an aspect of adenosine control or metabolism which may or may not be a cyclic AMP-related cellular function.     

Immunofluorescent localization of cyclic nucleotide-dependent protein kinases on the mitotic apparatus of cultured cells

Cyclic nucleotides and cyclic nucleotide-dependent protein kinases have been implicated in the regulation of cell motility and division, processes that depend on the cell cytoskeleton. To determine whether cyclic nucleotides or their kinases are physically associated with the cytoskeleton during cell division, fluorescently labeled antibodies directed against cyclic AMP, cyclic GMP, and the cyclic nucleotide- dpendent protein kinases were used to localize these molecules in mitotic PtK1 cells. Both the cyclic GMP-dependent protein kinase and the type II regulatory subunit of the cyclic AMP-dependent protein kinase were localized on the mitotic spindle. Throughout mitosis, their distribution closely resembled that of tubulin. Antibodies to cyclic AMP, cyclic GMP, and the type I regulatory and catalytic subunits of the cyclic AMP-dependent protein kinase did not label the mitotic apparatus. The association between specific components of the cyclic neucleotide system and the mitotic spindle suggests that cyclic nucleotide-dependent phosphorylation of spindle proteins, such as those of microtubules, may play a fundamental role in the regulation of spindle assembly and chromosome motion.     

Guanosine cyclic monophosphate-dependent protein kinase from foetal calf heart. Purification, general properties and catalytic subunit.

Cyclic GMP-dependent protein kinase was purified from foetal calf hearts, and its general properties and subunit structure were studied. The enzyme was purified over 900-fold from the heart extract by pH 5.3-isoelectric precipitation, DEAE-cellulose chromatography, Sephadex G-200 filtration and hydroxyapatite treatment. The purified myocardial enzyme, free from cyclic AMP-dependent protein kinase contamination, exhibited an absolute requirement of stimulatory modulator (or crude modulator containing the stimulatory modulator component) for its cyclic GMP-stimulated activity. Inhibitory modulator (protein inhibitor) of cyclic AMP-dependent protein kinase could not stimulate nor inhibit the cyclic GMP target enzyme. The enzyme had Ka values of 0.013, 0.033 and 3.0 micronM for 8-bromo cyclic GMP, cyclic GMP and cyclic AMP respectively. The cyclic GMP-dependent enzyme required Mg2+ and Co2+ for its activity, with optimal concentrations of about 30 and 0.5 mM respectively. The pH optimum for the enzyme activity ranged from 6 to 9. Histones were generally effective substrate proteins. The enzyme exhibited a greater affinity for histones than did the cyclic AMP-dependent class of protein kinase. The holoenzyme (apparent mol.wt. 150 000) of the myocardial cyclic GMP-dependent protein kinase was dissociated into a cyclic GMP-independent catalytic subunit (apparent mol.wt. 60 000) by cyclic GMP and histone. The catalytic subunit required the stimulatory modulator for its activity, as in the case of the holoenzyme in the presence of cyclic GMP.     

Characteristics of a new binding protein distinct from the kinase for guanosine 3':5'-monophosphate in rat platelets

A new type of cyclic GMP binding protein was recently identified in our laboratory (Hamet, P. and Coquil, J.-F. (1978) J. Cyclic Nucleotide Res. 4, 281--290). The binding, recovered in the supernatant fractions, is highly specific for cyclic GMP and is clearly distinct from the binding to cyclic GMP-dependent protein kinase. Chromatography on DEAE-Sepharose separated the cyclic GMP binding protein from cyclic AMP binding, cyclic AMP-dependent kinase activities, and from guanylate cyclase. The optimal binding occurs at high pH and in the presence of thiol reagents. Several phosphodiesterase inhibitors increase the affinity of binding (Kd was 353 +/- 60 nM in the absence and 13.4 +/- 1.5 nM in the presence of 1-methyl-3-isobutyl-xanthine). The molecular weight of the binding protein was determined to be about 176,000 and the sedimentation coefficient was 6.4 S. While the binding and phosphodiesterase activities co-migrated on DEAE-Sepharose, gel filtration and sucrose gradients, certain treatments (such as increasing the concentrations of salt and heating) were able to influence one activity while having no effect on the other. Hence, the binding activity may be involved in the regulation of the activity of cyclic GMP phosphodiesterase. Since the binding protein appears to be the only 'receptor' for cyclic GMP detectable in platelets, this protein and/or its relation to cyclic GMP phosphodiesterase may play a role in the mechanism of action of cyclic GMP in platelets.     

Characteristics of a new binding protein distinct from the kinase for guanosine 3′:5′-monophosphate in rat platelets

A new type of cyclic GMP binding protein was recently identified in our laboratory (Hamet, P. and Coquil, J.-F. (1978) J. Cyclic Nucleotide Res. 4, 281–290). The binding, recovered in the supernatant fractions, is highly specific for cyclic GMP and is clearly distinct from the binding to cyclic GMP-dependent protein kinase. Chromatography on DEAE-Sepharose separated the cyclic GMP binding protein from cyclic AMP binding, cyclic AMP-dependent kinase activities, and from guanylate cyclase. The optimal binding occurs at high pH and in the presence of thiol reagents. Several phosphodiesterase inhibitors increase the affinity of binding (K_d was 353 ± 60 nM in the absence and 13.4 ± 1.5 nM in the presence of 1-methyl-3-isobutyl-xanthine). The molecular weight of the binding protein was determined to be about 176 000 and the sedimentation coefficient was 6.4 S. While the binding and phosphodiesterase activities co-migrated on DEAE-Sepharose, gel filtration and sucrose gradients, certain treatments (such as increasing the concentrations of salt and heating) were able to influence one activity while having no effect on the other. Hence, the binding activity may be involved in the regulation of the activity of cyclic GMP phosphodiesterase. Since the binding protein appears to be the only ‘receptor’ for cyclic GMP detectable in platelets, this protein and/or its relation to cyclic GMP phosphodiesterase may play a role in the mechanism of action of cyclic GMP in platelets.     

Alterations in activities of cyclic nucleotide systems and in beta-adrenergic receptor-mediated activation of cyclic AMP-dependent protein kinase during progression and regression of isoproterenol-induced cardiac hypertrophy.

Initial and transient increases in the basal levels of cyclic GMP in the heart were noted prior to cardiac hypertrophy in rats administered isoproterenol. Increased levels of cyclic AMP-phosphodiesterase (in both the soluble and particulate fractions) and stimulatory modulator of cyclic GMP-dependent protein kinase, however, were associated with the progression, or the state, of cardiomegaly, with their levels returning to the control values upon regression of the hypertrophy. The levels of cyclic GMP phosphodiesterase in the soluble fraction were lower, whereas those in the particulate fraction were higher, in the hypertrophied heart than the control. In cardiac hypertrophy, the maximal activity ratio(--cyclic AMP/+cyclic AMP) of cyclic AMP-dependent protein kinase in the incubated minced heart caused by isoproterenol was lower, whereas the concentration of isoproterenol required to increase the activity ratio half-maximally was higher than controls; the reduced responsiveness to the drug, however, was reversed when the hypertrophy regressed. These observations, taken collectively, appear to suggest that the desensitization of the beta-adrenergic mechanism seen in the cardiac hypertrophy produced by repeated administration of isoproterenol is associated with adaptive modifications in certain parameters of the cyclic nucleotide systems.     

Subcellular alterations in cyclic AMP-binding and protein kinase activities during ontogeny in the rat cerebellum

Ontogenic relationships between levels of cyclic AMP-binding activity and protein kinase activity were examined in subcellular fractions of the cerebellum during the first 3 weeks of neonatal life. A progressive increase in cyclic AMP levels was paralleled by an increase in cyclic AMP bindign by the nuclear and cytosol fractions, but not by the mitochondrial or microsomal fractions. Utilization of heat-stable protein kinase inhibitor permtited distinction of the cyclic AMP-dependent from the cyclic AMP-independent form of the protein kinase population. Cyclic AMP-dependent protein kinase increased between days 4 and 20 to represent a progressively greater proportion of the protein kinase population. In all subcellular fractions alterations of cyclic AMP-dependent protein kinase during neonatal development paralleled changes in binding of cyclic AMP to protein in these fractions. In both the nuclear and cytosol fractions cyclic AMP-dependent protein kinase activity increased progressively between days 4 and 20, i.e. 64 ± 6 to 176 ± 16 and 79 ± 12 to 340 ± 12 pmol/min per mg protein, respectively. Cyclic AMP-dependent protein kinase activity in the mitochondrial fraction declined during the postnatal period studied, and in the microsomal fraction it rose to a non-sustained peak at 14 days and fell thereafter. Unlike the cyclic AMP-dependent form, cyclic AMP-independent protein kinase activity did not follow the ontogenetic pattern of cyclic AMP-binding activity. The specific activity of nuclear cyclic AMP-independent protein kinase did not change during days 4–20, and a non-sustained rise of cyclic AMP-independent protein kinase activity in both cytosol and microsomal fractions during the 7th–12th day tended to parallel more closely known patterns of postnatal proliferative growth. The findings reported herein indicate that the ontogenic pattern of cyclic AMP-dependent protein kinase varies between different subcellular fractions of the neonatal cerebellum, that these patterns parallel the changes in cyclic AMP-bidign activity, and suggest that the component parts of the cyclic AMP system may develop as a functional unit.     

Alterations in activities of cyclic nucleotide systems and in β-adrenergic receptor-mediated activation of cyclic amp-dependent protein kinase during progression and regression of isoproterenol-induced cardiac hypertrophy

Initial and transient increases in the basal levels of cyclic GMP in the heart were noted prior to cardiac hypertrophy in rats administered isoprotenol. Increased levels of cyclic AMP-phosphodiesterase (in both the soluble and particulate fractions) and stimulatory modulator of cyclic GMP-dependent protein kinase, however, were associated with the progression, or the state, of cardiomegaly, with their levels returning to the control values upon regression of the hypertrophy. The levels of cyclic GMP phosphodiesterase in the soluble fraction were lower, whereas those in the particulate fraction were higher, in the hypertrophied heart than the control. In cardiac hypertrophy, the maximal activity ratio (?cyclic AMP/+cyclic AMP) of cyclic AMP-dependent protein kinase in the incubated minced heart caused by isoproterenol was lower, whereas the concentration of isoproterenol required to increase the activit ratio half-maximally was higher than controls; The reduced responsiveness to the drug, however, was reversed when the hypertrophy regressed. These observations, taken collectively, appear to suggest that the desensitization of the β-adrenergic mechanism seen in the cardiac hypertrophy produced by repeated administration of isoproterenol is associated with adaptive modifications in certain parameters of the cyclic nucleotide systems.     

Modified cyclic nucleotide systems in Morris hepatoma 3924A favoring expression of cyclic GMP effect

Modifications in the cyclic nucleotide systems favoring the expression of cyclic GMP effects were found to occur in the transplanted fast-growing Morris hepatoma 3924A. These included: (a) a decreased level of cyclic GMP phosphodiesterase and an increased level of cyclic AMP phosphodiesterase; (b) a disproportionately increased level of cyclic GMP-dependent protein kinase relative to that of cyclic AMP-dependent protein kinase; (c) a disproportionately increased level of stimulatory modulator of cyclic GMP-dependent protein kinase relative to that of inhibitory modulator of cyclic AMP-dependent protein kinase; and (d) an increased level of phosphoprotein phosphatase.     

Photoaffinity labeling of three renal cyclic 3′,5′-adenosine monophosphate-binding proteins

Evidence is presented for the presence of multiple cyclic AMP binding components in the plasma membrane and cytosol fractions of porcine renal cortex and medulla. N⁶-(Ethyl-2-diazomalonyl)-3′,5′-adenosine monophosphate, a photoaffinity label for cyclic AMP binding sites, exhibits non-covalent binding characteristics similar to cyclic AMP in membrane and soluble fractions. Binding data for either compound to the plasma membrane fraction yields biphasic Scatchard plots while triphasic plots are obtained with the dialyzed cytosol. When covalently labeled fractions are separated on SDS-polyacrylamide gel electrophoresis, the cyclic AMP photoaffinity label is found on 49 000 and 130 000 dalton components in each kidney fraction. DEAE-cellulose and gel filtration chromatography of the labeled cortical cytosol fraction establishes that the three components suggested by the binding data correspond to two 49 000 dalton species and a 130 000 component. The 49 000 species have higher affinities for cyclic AMP than the 130 000 component (K_a(1) = 2.0 · 10⁹, K_a(2) = 1.7 · 10⁸, K_a(3) = 1.0 · 10⁷). The 49 000 components are associated with protein kinase activity while the 130 000 component does not exhibit protein kinase, adenosine deaminase, or cyclic nucleotide phosphodiesterase activity. Immunologic results and effects of phosphorylation and cyclic GMP on cyclic AMP binding further suggest that the 49 000 components are regulatory subunits of cyclic AMP-dependent protein kinases. Cyclic AMP binding to the 130 000 component is markedly inhibited by adenosine and adenine nucleotides, but not cyclic GMP. Thus, this component may reflect an aspect of adenosine control or metabolism which may or may not be a cyclic AMP-related cellular function.     

Modified cyclic nucleotide systems in Morris hepatoma 3924A favoring expression of cyclic GMP effect.

Modifications in the cyclic nucleotide systems favoring the expression of cyclic GMP effects were found to occur in the transplanted fast-growing Morris hepatoma 3924A. These included: (a) a decreased level of cyclic GMP phosphodiesterase and an increased level of cyclic AMP phosphodiesterase; (b) a disproportionately increased level of cylic GMP-dependent protein kinase relative to that of cyclic AMP-dependent protein kinase; (c) a disproportionately increased level of stimulatory modulator of cyclic AMP-dependent protein kinase relative to that of inhibitory modulator of cyclic AMP-dependent protein kinase; and (d) an increased level of phosphoprotein phosphatase.     

Protein phosphorylation in human peripheral blood lymphocytes. Subcellular distribution and partial characterization of adenosine 3'':5''-cyclic monophosphate-dependent protein kinase.

Cytoplasmic and membrane fractions prepared from human peripheral-blood lymphocytes both contained cyclic AMP-dependent protein kinase activity and endogenous protein kinase substrates. Protein kinase activity in the particulate fractions was not eluted with 0.25 M-NaCl, suggesting that it was not derived from non-specifically absorbed soluble cytoplasmic protein kinase. Nor was the particulate protein kinase activity eluted by treatment with cyclic AMP, suggesting that the catalytic subunit is membrane-bound and arguing against cyclic AMP-induced translocation of particulate activity. Cyclic AMP-dependent protein-phosphorylating activity in the cytoplasmic fraction was highly sensitive to inhibition by Mn2+, and was co-eluted from DEAE-cellulose primarily with type-I rabbit skeletal-muscle kinase. Cyclic AMP-dependent phosphorylating activity in the plasma-membrane fractions was stimulated at low [Mn2+] and inhibited only at high [Mn2+]. When solubilized with Nonidet P-40, plasma-membrane protein kinase was co-eluted from DEAE-cellulose with type-II rabbit muscle kinase. These differences, together with the strong association of the particulate kinases with the particulate fraction, suggest the possibility of compartmentalized protein phosphorylation in intact lymphocytes.     

Separation of cyclic AMP and cyclic GMP from thymidine,electrolytes and polyvalent nucleotides in tissue samples

Cyclic AMP and cyclic GMP can be separated from thymidine and its possible metabolites, electrolytes, and polyvalent nucleotides using columns of acidic alumina. Electrolytes and thymidine are not adsorbed on acidic alumina at pH 4.4 while cyclic nucleotides and polyvalent nucleotides are adsorbed at this pH. Cyclic AMP and cyclic GMP are eluted together from acidic alumina with 0.2 M ammonium formate (pH 6.0) and the polyvalent nucleotides remain adsorbed. The cyclic nucleotides are separated by chromatography on Dowex AG 1 X 8 resin. Recovery is 60–64% for cyclic AMP and cyclic GMP isolated from renal tissue samples. This methodology permits the separation of tritiated thymidine from cyclic nucleotides which are present in tissue preparations used in studies on the role of cyclic nucleotides in cellular growth.     

Two types of cyclic GMP binding site associated with the cyclic AMP-dependent protein kinase from lymphocytes.

Low- and high-affinity binding sites for cyclic GMP were found to be associated with the cyclic AMP-dependent protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) from human tonsillar lymphocytes, but neither of them was identical with the cyclic AMP binding site. The enzyme activated by cyclic GMP phosphorylated the same site of calf thymus H2b histone as the cyclic AMP activated enzyme; however, more complex kinetics of activation were found with cyclic GMP. Two classes of cyclic GMP binding site were demonstrated by kinetic analysis of cyclic [3H]GMP binding in the enzyme preparations eluted by 0.1 M potassium phosphate (pH 7.0) from DEAE cellulose. The high-affinity cyclic GMP binding site (Kd about 4 . 10(-8) M) belonged to some complex form of the protein kinase, as evidenced by the mutual inhibition of cyclic AMP binding and high affinity cyclic GMP binding. However, the high-affinity cyclic GMP binding site disappeared on Sephadex G-100 gel chromatography of the enzyme preparation, whereas the cyclic AMP binding activity was recovered quantitively as separate fractions. The low-affinity cyclic GMP binding site (Kd 2--5 . 10(-6) M) was demonstrated by the inhibitory effect of 10(-5) M cyclic GMP on cyclic AMP binding in each cyclic AMP binding fraction obtained by gel chromatography. However, cyclic AMP did not inhibit the binding of cyclic GMP to the low-affinity binding site.     

Separation of cyclic AMP and cyclic GMP from thymidine, electrolytes and polyvalent nucleotides in tissue samples.

Cyclic AMP and cyclic GMP can be separated from thymidine and its possible metabolites, electrolytes, and polyvalent nucleotides using columns of acidic alumina. Electrolytes and thymidine are not adsorbed on acidic alumina at pH 4.4 while cyclic nucleotides and polyvalent nucleotides are adsorbed at this pH. Cyclic AMP and cyclic GMP are eluted together from acidic alumina with 0.2 M ammonium formate (pH 6.0) and the polyvalent nucleotides remain adsorbed. The cyclic nucleotides are separated by chromatography on Dowex AG 1 X 8 resin. Recovery is 60--64% for cyclic AMP and cyclic GMP isolated from renal tissue samples. This methodology permits the separation of tritiated thymidine from cyclic nucleotides which are present in tissue preparations used in studies on the role of cyclic nucleotides in cellular growth.     

Increased Cyclic AMP-Dependent Protein Kinase Activity in Postmortem Brain from Patients with Bipolar Affective Disorder

Previous observations of reduced [3H]cyclic AMP binding in postmortem brain regions from bipolar affective disorder subjects imply cyclic AMP-dependent protein kinase function may be altered in this illness. To test this hypothesis, basal and stimulated cyclic AMP-dependent protein kinase activity was determined in cytosolic and particulate fractions of postmortem brain from bipolar disorder patients and matched controls. Maximal enzyme activity was significantly higher (104%) in temporal cortex cytosolic fractions from bipolar disorder brain compared with matched controls. In temporal cortex particulate fractions and in the cytosolic and particulate fractions of other brain regions, smaller but statistically nonsignificant increments in maximal enzyme activity were detected. Basal cyclic AMP-dependent protein kinase activity was also significantly higher (40%) in temporal cortex cytosolic fractions of bipolar disorder brain compared with controls. Estimated EC50 values for cyclic AMP activation of this kinase were significantly lower (70 and 58%, respectively) in both cytosolic and particulate fractions of temporal cortex from bipolar disorder subjects compared with controls. These findings suggest that higher cyclic AMP-dependent protein kinase activity in bipolar disorder brain may be associated with a reduction of regulatory subunits of this enzyme, reflecting a possible adaptive response of this transducing enzyme to increased cyclic AMP signaling in this disorder.