Functional specificity of guanosine 3':5'-monophosphate-dependent and adenosine 3':5'-monophosphate-dependent protein kinases from silkworm

Opposing functional effects of cyclic GMP and cyclic AMP may act through protein phosphorylation in rabbit cardiac myocytes

1. We tested the hypothesis that the negative functional effects of cyclic GMP (cGMP) oppose the positive effects of cyclic AMP (cAMP) in cardiac myocytes through interaction at the level of their respective protein kinases. 2. Cell shortening was studied using a video-edge detector. The O2 consumption of a suspension of rabbit ventricular myocytes was measured using O2 electrodes. Protein phosphorylation was measured autoradiographically following SDS-PAGE. Data were collected with: (1) 8-bromo-cGMP (8-Br-cGMP) 10(-7) or 10(-5) M; (2) 8-bromo-cAMP (8-Br-cAMP) 10(-7) or 10(-5) M; (3) 8-Br-cAMP 10(-5) M followed by 8-Br-cGMP 10(-7) or 10(-5) M; (4) 8-Br-cGMP 10(-5) M followed by 8-Br-cAMP 10(-7) or 10(-5) M; (5) 8-Br-cGMP 10(-7) or 10(-5) M followed by KT 5720 (cAMP-dependent protein kinase inhibitor) or KT 5823 (cGMP-dependent protein kinase inhibitor) 10(-6) M; and (6) 8-Br-cAMP 10(-7) or 10(-5) M followed by KT 5720 or KT 5823 10(-6) M. 3. 8-Br-cGMP 10(-5) M decreased percent shortening (Pcs) from 6.3+/-0.6 to 3.6+/-0.4% and rate of shortening (Rs) from 66.7+/-4.4 to 41.8+/-4.2 microm s(-1). 8-Br-cAMP 10(-5) M increased Pcs (from 3.7+/-0.2 to 4.8+/-0.2) and Rs (from 50.0+/-3.0 to 60.0+/-3.1). With 8-Br-cAMP 10(-5) M, 8-Br-cGMP 10(-5) M decreased Pcs and Rs less. The positive functional effects of 8-Br-cAMP 10(-7) or 10(-5) M were also diminished with 8-Br-cGMP 10(-5) M. Following 8-Br-cGMP 10(-7) or 10(-5) M, KT 5720 10(-6) M further decreased Pcs to 2.5+/-0.3 and Rs to 30.0+/-4.1. KT 5823 10(-6) M returned Pcs to 4.7+/-0.4 and Rs to 61.3+/-5.3. Following 8-Br-cAMP 10(-7) or 10(-5) M, KT 5720 decreased the elevated Pcs and Rs significantly and KT 5823 10(-6) M further increased these parameters. 4. cGMP and cAMP phosphorylated the same five protein bands. With KT 5720 or KT 5823, all of the bands were lighter at the same concentration of 8-Br-cAMP and 8-Br-cGMP. 5. We conclude that, in rabbit ventricular myocytes, the opposing functional effects of cGMP and cAMP are related to the interaction at the level of their respective protein kinases.

Both IgM and IgG anti-VSG antibodies initiate a cycle of aggregation-disaggregation of bloodstream forms of Trypanosoma brucei without damage to the parasite

Bloodstream forms of Trypanosoma brucei, when aggregated in the presence of either acute immune plasma, acute immune serum, purified IgM anti-VSG antibodies or purified IgG anti-VSG antibodies, subsequently disaggregated with a t1/2 for disaggregation of 15 min at 37 degrees C as long as the trypanosomes were metabolically active at the beginning of the experiment and maintained during the experiment in a suitable supporting medium. The t1/2 for disaggregation was found to be directly dependent upon temperature and inversely proportional to the antibody concentration. The trypanosomes were always motile and metabolically active during aggregation and after disaggregation and were fully infective for a mammalian host following disaggregation as well as able to grow and divide normally during axenic culture. The disaggregation was strictly energy dependent and was inhibited when intracellular ATP levels were reduced by salicylhydroxamic acid or following addition of oligomycin while respiring glucose. In addition the process of disaggregation was dependent upon normal endosomal activity as evidenced by its sensitivity to a wide variety of inhibitors of various endosomal functions. Disaggregation was not due to separation of immunoglobulin chains by either disulphide reduction or disulphide exchange reactions and gross proteolytic cleavage of the immunoglobulins attached to the surface of the parasite was not detected. In addition, gross cleavage or release of the VSG from the surface of the cell did not occur during disaggregation but proteolytic cleavage of a small proportion of either the VSG or the immunoglobulins could not be eliminated from consideration. Finally the mechanism of disaggregation was found to be a regulated process, independent of Ca2+ movements but dependent upon the activity of protein kinase C or related kinases and inhibited by the activity of protein kinase A as evidenced by the effects of a panel of inhibitors and cAMP analogues on the process of disaggregation. The mechanism of disaggregation displayed by trypanosomes aggregated by anti-VSG antibody is proposed to form part of the parasite's defence against the host immune system and functions to aid survival of trypanosomes in the presence of antibody in the host prior to the occurrence of a VSG switching event.

Cyclic AMP-dependent protein kinase in ovarian follicle cells of starfish Asterina pectinifera

Adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA) in ovarian follicle cells of the starfish Asterina pectinifera was studied. Protein kinase activity in follicle cell homogenate was activated by cAMP in a dose-dependent manner, and Ka was obtained with 10(-7) M cAMP. The PKA activity required Mg2+ at concentrations between 2 and 10 mM. On Sephacryl S-300 column chromatography of partially purified PKA, Mr of the holoenzyme was estimated to be about 180,000. [2,3-3H]cAMP binding activity also suggested a regulatory subunit of Mr about 50,000. DE-52 column chromatography of the cell extract resolved the enzyme activity into two peaks, which eluted between 0.05 and 0.1 M NaCl (type I), and between 0.15 and 0.25 M NaCl (type II). The type I enzyme was the predominant form of PKA in starfish follicle cells. In a cell-free system, a 70 kDa protein was phosphorylated during incubation with [gamma-32P]ATP in the presence of cAMP. These results suggest that PKA stimulates the phosphorylation of a 70 kDa protein following an increase in the level of cAMP.

Characterization of a basic polypeptide-activated protein kinase in the eggs of the silkworm, Bombyx mori

A basic polypeptide-activated protein kinase (designated BA-kinase), which requires Mn2+ rather than Mg2+ for its activity, has been highly purified from a 1.5 M KCl extract of fertilized and unfertilized eggs of the silkworm, Bombyx mori. It was found that (i) the molecular weight of the purified protein kinase was approx. 260,000; (ii) the kinase phosphorylated vitellin, protamine and casein in a cAMP-, cGMP- and Ca2(+)-independent manner; (iii) the kinase phosphorylated only threonine residues when casein was used as a phosphate acceptor; (iv) protein phosphorylation by the kinase was remarkably stimulated by basic polypeptides, such as histone, polyArg and polyLys; and (v) the purified kinase had an affinity with DNA, but not with RNAs. Moreover, the observations that (a) the BA-kinase activity and phosphorylation of polypeptides by the kinase in the 1.5 M KCl egg extract greatly increased after fertilization, and (b) polypeptides, from this extract, of 16.5-21 kDa, which were highly phosphorylated by the kinase but not by A- or G-kinases, appeared within 4 h after fertilization, suggest that a basic polypeptide activated protein kinase (BA-kinase) may play an important role in the progression of embryogenesis through specific phosphorylation of yolk proteins by the kinase, in the presence of nucleic basic proteins.

Mechanistic studies of cAMP-dependent protein kinase action

The details of the process by which protein kinase catalyzes phosphoryl group transfers are beginning to be understood. Early work that explored the primary specificity of cAMP-dependent protein kinase action enabled the synthesis of small peptide substrates for the enzyme. Enzyme-peptide interactions seem simpler to understand than protein-protein interactions, so peptide substrates have been used in most protein kinase studies. In most investigations the kinetics for the phosphorylation of small peptides have been interpreted as being consistent with mechanisms which do not invoke phospho-enzyme intermediates (see, for example, Bolen et al.). Protein kinase has been shown to bind two metal ions in the presence of a nucleotide. Using magnetic resonance techniques the binding of these ions has been utilized to elucidate the conformation of nucleotide and peptide substrates or inhibitors when bound in the enzymic active site. Also, two new peptides with the form Leu-Arg-Arg-Ala-Ser-Y-Gly, where Y was either Pro or (N-methyl)Leu, were synthesized and found not to be substrates, within the limits of detection, for protein kinase. The striking lack of affinity that protein kinase has for such peptides which are unlikely to form a beta 3-6 turn has not been reported before. Our results may indicate that this type of turn is a requirement for protein kinase catalyzed phosphorylation or that these peptides lack the ability to form a particular hydrogen bond with the enzyme. Magnetic resonance techniques have indicated that the distance between the phosphorous in the gamma-phosphoryl group of MgATP and the hydroxyl oxygen of serine in the peptide Leu-Arg-Arg-Ala-Ser-Leu-Gly is 5.3 +/- 0.7 A. This, together with certain kinetic evidence, suggests that the mechanism by which protein kinase catalyzes phosphoryl group transfer has considerable dissociative character. Chemical modifications, including one using a peptide-based affinity label, have identified two residues at or near the active site, lysine-72 and cysteine 199. While neither of these groups has been shown to be catalytically essential, similar studies may help to identify groups that are directly involved in the catalytic process. Finally, a spectrophotometric assay for cAMP-dependent protein kinase has been described. Using this assay the preliminary results of an in-depth study of the pH dependence of protein kinase catalyzed phosphoryl group transfer have been obtained. This study shall aid in the identification of active site residues and should contribute to the elucidation of the enzyme's catalytic mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

cAMP-dependent protein kinases from the insect Ceratitis capitata

Among the components of the two cyclic nucleotide system of Ceratitis capitata pharate adults, two cAMP-dependent protein kinase activities have been identified and purified through a sequence of chromatographic procedures. The properties of both protein kinases, A-1 and A-2, were studied and characterized in comparison with those of other sources. Protein kinase A-2 from Ceratitis capitata corresponds to type I from mammals mainly concerning about the dissociating effect of histones. Protein kinase A-2 exhibited a molecular weight of 39,000 in the presence of cAMP, whereas in the absence of the cyclic nucleotide two components of 80,000 and 159,000 were present and attributed to the forms RC and R2C2, respectively. Protein kinase activities A-1 and A-2 were markedly inhibited by increasing ionic strength whereas the activity (-cAMP/+cAMP) ratio for protein kinase A-2 increased versus NaCl concentration. Histones H1 and H2B were the best substrates for both A-1 and A-2 activities; the high mobility group of insect proteins (HMG) were also notably phosphorylated by A-2 preparation. Among the cyclic nucleotides assayed for the protein kinase activity A-2, cAMP induced a high activation at the lowest concentrations although high cAMP concentrations decreased the protein kinase activity, possibly through binding to the catalytic site. The protein kinase A-2 preparations exhibited a complex kinetics due to the presence of two forms with different affinity for ATP; these forms may be related to the aggregation properties of the enzyme.

Calmodulin and acidic compounds alter basic protein phosphorylation by the protein kinase from human platelets

A cyclic nucleotide-independent protein kinase of human platelets, which phosphorylated histones, myelin basic protein and protamine and did not catalyze the phosphorylation of acidic proteins such as casein, phosvitin and myosin light chain, has been purified approx. 1,500-fold from the crude extract by steps of DEAE-cellulose, Sephadex G-200, hydroxylapatite and phosphoryl cellulose column chromatography. The substrate phosphorylation by this kinase was markedly enhanced by calmodulin even in the absence of Ca2+, when mixed histone was used as a substrate. The interaction of the kinase with mixed histone resulted in an irreversible inactivation of the enzyme. Calmodulin prevented this inactivation, and this compound produced an apparent increase in histone phosphorylation by the kinase. It should be noted that acidic polypeptides such as troponin-C, phospholipids and nucleic acids have a similar ability. The addition of Ca2+ reduced the effect of calmodulin more than the effects of other acidic compounds.

Regulation of guinea pig heart phosphorylase kinase by cAMP, protein kinase, and calcium

In skeletal muscle the activation of phosphorylase kinase (PK) associated with phosphorylation of the enzyme can be measured as an increase in the pH 6.8:8.2 activity ratio. Phosphorylation leads to a 20- to 30-fold increase in PK activity (PKA) at pH 6.8 and a large decrease in the Km for phosphorylase. Perfused guinea pig hearts exposed to isoproterenol (0.3 microM) showed an increase in PKA, but without an increase in the pH 6.8:8.2 activity ratio. In a 10-fold dilution of guinea pig heart cytosol exposed to cAMP + methylisobutylxanthine, PKA was stimulated twofold at pH 7.5. Addition of exogenous protein kinase stimulated PKA fourfold. Both methods of activation were reversible and were blocked by the heat-stable inhibitor of protein kinase. Guinea pig heart PK was Ca2+-dependent requiring 0.6 microM Ca2+ for half-maximal activity. Kinetic studies indicate that the Km of guinea pig heart PK for phosphorylase b at pH 6.8 is not markedly reduced after in vitro activation (35%). This could explain the observed lack of increase in the pH 6.8:8.2 activity ratio after exposure of hearts to isoproterenol. The time course for the activation of inotropic state and the glycogenolytic pathway in perfused guinea pig hearts by isoproterenol showed that these processes were maximally activated within 25 s. However, PK remained activated for 2 min, long after the other biochemical and physiological parameters had returned to control values. These data suggest that Ca2+, not phosphorylation state, is important in regulating the return of dP/dt to control levels after beta-adrenergic stimulation.

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.

Phosphorylation of endogenous proteins by endogenous protein kinase of density gradient--purified plasma membrane vesicles of Ehrlich cells

A phosphorylation of endogenous acceptor protein(s) has been demonstrated to occur in membraneous vesicles prepared from Ehrlich ascites tumour cells. The reaction was catalyzed by endogenous protein kinase in the presence of exogenous (gamma32P)ATP. A considerable increase of the specific protein kinase activity took place when the plasma membrane preparation was subjected to a further gradient centrifugation in Dextran T 150. This was done in the presence of a slightly alkaline phosphate buffer containing Mg-ions which resulted in the formation of a well defined vesicular preparation at density 1.035 in the gradient. The apparent Km and Vmax for the reaction with vesicles and exogenous (gamma32P)ATP were determined and found to be 0.022 mM and 0.23 nmol x mg-1 x 10 min-1, respectively. Neither cyclic AMP nor cyclic GMP did stimulate the protein kinase-catalyzed reaction. Instead, a clear inhibition of the reaction by the cyclic nucleotides was unexpectedly registered. Adenosine at 0.5 mM also inhibited the reaction. Calcium ions were inhibitory at all concentrations tested in the presence of a fixed (gamma32P)ATP/Mg2+ ratio. When Mg-ions were stoichiometrically replaced by Ca-ions practically no activity was observed.

Evidence for a role of sulfhydryl groups in catalytic activity and subunit interaction of the cyclic GMP-dependent protein kinase from silkworm

Guanosine 3':5'-monophosphate-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37) has been isolated from silkworm pupal fat body (Bombyx mori) which is devoid of any adenosine 3':5'-monophosphate-dependent protein kinase. The enzyme displayed catalytic properties which were roughly similar to those described for adenosine 3':5'-monophosphate-dependent protein kinase. This similarity has been found in substrate specificity, optimal Mg2+ dependency, polyamines effects and the lack of dependency upon sulfhydryl compound for activation by cyclic GMP. Treatment of the enzyme with sulfhydryl reagents, N-ethylmaleimide or p-chloromercuribenzoic acid, inhibited the catalytic activity as well as the dissociation of the binding and catalytic activities as shown by means of sucrose-density gradient ultracentrifugation. In the presence of cyclic GMP or histone, the disulfide-linked structure did not dissociate into separate subunits nor did it migrate as the holoenzyme but sedimented as an intermediate form carrying both binding and catalytic activities.

Cyclic nucleotide metabolism in solid tumor tissues

The examination of the regulation of the system of 3'-5' cyclic nucleotide monophosphates has only begun in cancer tissues. In human cancers, these studies are notably non-existent. However, in animal cancers, especially the Morris hepatomas, enough data has been gathered that, while risky, certain trends seem to begin to appear. Cyclic AMP is constant or lowered, while cyclic GMP is elevated in the fast growing hepatomas. Regulation of adenylate cyclase by protein hormones is reduced, while regulation by epinephrine may be increased. Binding of glucagon is decreased in the fast growing hepatomas. Guanylate cyclase, while being predominantly cytoplasmic in the normal liver, is predominantly membrane bound in the tumors. The liver enzyme is also readily stimulated by several chemical carcinogens. The cyclic GMP phosphodiesterases are decreased in these tumors; while the cAMP phosphodiesterases are increased. Although the cyclic nucleotide dependent protein kinases (histone as substrate) are altered in the hepatomas, observations of unique cyclic nucleotide binding proteins or cAMP independent protein kinases in cancer tissues may be of even greater significance for the development of or the maintenance of the neoplastic state of cells.

Cyclic nucleotide phosphodiesterases of Hyalophora cecropia silkmoth fat body

Two soluble forms of 3':5'-cyclic-nucleotide phosphodiesterase (o':5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) were found in the larval fat body of the silkmoth Hyalophora cecropia. These differ in elution profile on Sephadex G-200, solubility in ammonium sulfate, metal ion requirements and kinetic properties. Phosphodiesterase I has Km values of 11 muM and 1.8 muM for cyclic AMP and cyclic GMP, respectively, has 5-fold greater maximal activity with cyclic AMP than with cyclic GMP, and is activated by Mg2+ and Co2+, and inhibited by EDTA. phosphodiesterase II has Km values of 625 muM and 125 muM for cyclic AMP and cyclic GMP, respectively, has similar maximal activity with both substrates, and is not activated by divalent metal ions or inhibited by EDTA. Cyclic nucleotides and methylxanthines competitively inhibit both enzymes. Phosphodiesterase is found in both soluble and particulate fractions of homogenates. Total activity is highest during the larval stage of the insect, drops markedly following pupation, and rises again during pharate adult development.

Cyclic 3',5'-GMP independent protein kinase at the outer surface of intact Ehrlich cells

The phosphoryl group transfer from (gamma(32)P)ATP into acceptor proteins by an endogenous protein kinase at the surface of Ehrlich cells has been further studied as regards possible stimulation by different concentrations of dibuturyl cyclic guanosine monophosphate (3',5'-GMP). Using the endogenous acceptor protein of the surface of Ehrlich cells the cyclic nucleotide had no stimulatory effect on the protein kinase of the plasma membrane. The lack of stimulatory action of the cyclic nucleotide was also observed when an exogenous acceptor protein was present. Instead, a slight inhibitory effect was usually seen in both types of experiments. Labeled phosphorylserine was always in excess of labeled phosphoryl threonine. Both were isolated from hydrolyzed acceptor proteins. The lack of stimulation by a cyclic nucleotide on the phosphorylation of acceptor protein(s) on the cell surface does not rule out a regulatory function by the protein kinase of the plasma membrane. Instead, we propose an autoregulatory mechanism for the phosphorylation at the cell surface. This mechanism is based upon the high sensitivity of the enzyme to Ca-ions.

Experimental study on renal and hepatic glucose metabolism in total gastrectomized dogs with special reference to glycolysis and glyconeogenesis

In spite of the extensive studies on glucose metabolism in surgical field, the postoperative renal and hepatic glucose metabolism and their interrelation have not been reported. The present study was undertaken to interrelate the metabolic states in the kidney and the liver in total gastrectomized dogs. In the kidney, the glycolysis was inhibited in the early postoperative stage whereas the gluconeogenesis was activated. In the late postoperative stage the glycolysis remained slightly inhibited, while the gluconeogenesis remained activated. In the liver, in the early postoperative stage the glycolysis was inhibited, whereas the gluconeogenesis was activated. The glycolysis in the late postoperative stage returned to the preoperative stage, while the gluconeogenesis remained inhibited. The gluconeogenesis in both kidney and liver was disturbed in the early postoperative stage while they were restored, but were reversed, in the late postoperative stage.