Dissociation of rabbit red blood cell cyclic AMP-dependent protein kinase I by protamine

Inhibition by glucose 6-phosphate of cyclic AMP-dependent protein kinase phosphorylation of glycogen synthase

Cyclic AMP-dependent protein kinase phosphorylates and inactivates glycogen synthase. In the absence of cyclic AMP, glycogen synthase is able to partially activate cyclic AMP-dependent protein kinase, probably by inducing the dissociation of the catalytic and regulatory subunits. The activation of cyclic AMP-dependent protein kinase by glycogen synthase is greatly reduced by the addition of low, physiological concentrations of the allosteric activator of glycogen synthase, glucose 6-phosphate. This effect appears to be specific for both glycogen synthase as substrate of the kinase and for cyclic AMP-dependent protein kinase as glycogen synthase phosphorylating enzyme. The result is an apparent, although not real effect of glucose 6-phosphate as an inhibitor competing with cyclic AMP. The reported inhibition by insulin of the activity of cyclic AMP-dependent protein kinase in skeletal muscle may be explained by the increased intracellular levels of glucose 6-phosphate resulting from the action of the hormone on glucose transport.

Polyamines and basic proteins stimulate activation by cAMP and catalytic activity of Mucor rouxii cAMP-dependent protein kinase

Partial activation of Mucor rouxii cAMP-dependent protein kinase by cAMP was obtained when kemptide was used as substrate, but complete activation was attained with cAMP plus protamine or histone. Full activation could not be achieved by increasing kemptide or cAMP concentration. Complete activation by cAMP could be obtained by addition of 10 microM polylysine, 10 microM lysine-rich histone or 0.5 mM spermine plus spermidine. The degree of stimulation could be up to 5-fold, depending on the amount of enzyme in the assay. The same concentrations of polycations increased 1.5-2.3-fold the Vmax of kemptide phosphorylation by the free catalytic subunits of both Mucor and bovine heart protein kinases; 10 microM polyarginine inhibited completely the activity of both enzymes.

Elution of the catalytic subunits of the type I and type II forms of cyclic AMP-dependent protein kinase within the type I chromatographic peak

The purpose of this investigation was to determine the elution location upon ion-exchange chromatography of the catalytic subunits of both the type I and type II isozyme forms of cAMP-dependent protein kinase. We show that ion-exchange chromatography with DEAE-Sepharose CL-6B yields an apparent type I chromatographic peak of cAMP-dependent protein kinase which can represent not only type I holoenzyme activity but also catalytic activity derived from either the type I or type II enzyme forms. Such knowledge of the elution location of the dissociated catalytic subunits can prevent incorrect identification of the distribution of cAMP-dependent protein kinase isozymes in studies which estimate the isozyme concentrations based on the relative proportions of the kinase activity peaks.

Protein kinase activity and endogenous phosphorylation in subfractions of rat liver mitochondria

Rat liver mitochondria were subfractionated into outer membrane, intermembrane and mitoplast (inner membrane and matrix) fractions. Of the recovered protein kinase activity, 80-90% was found in the intermembrane fraction, while the rest was associated with mitoplasts. The intermembrane protein kinase was stimulated by cyclic AMP, while the mitoplast enzyme was stimulated by the nucleotide only after treatment with Triton X-100. Extracted protein kinase resolved into three peaks on DEAE-cellulose chromatography. All three peaks were present both in the intermembrane fraction and in mitoplasts. One peak corresponded to the catalytic subunit of cyclic AMP-dependent protein kinases, one was a cyclic AMP-independent enzyme, and the third was the cyclic AMP-dependent type II enzyme. The endogenous incorporation of phosphate was particularly high in the outer mitochondrial membrane, and occurred also in the mitoplast fraction. The incorporation in mitoplasts was to a double band of Mr 47 500, and in outer membranes to apparently heterogeneous material of comparatively low molecular weight.

Determination of binding parameters of cyclic AMP and its analogs to cyclic AMP-dependent protein kinase by the fluorescent probe method

The method for determination of dissociation constants for cyclic AMP and its analogs bound to cyclic AMP-dependent protein kinase from pig brain is described. The technique for measuring the binding parameters of the ligands is based on the changes in the fluorescent spectrum of etheno cyclic AMP once it is bound to protein kinase. The dissociation constants for a number of nonfluorescent cyclic AMP analogs were determined in the competitive displacement of etheno cyclic AMP by these analogs. The number of cyclic AMP-binding sites in the pig brain protein kinase was found to be 2.2; no cooperativity was observed upon binding. The holoenzyme complex (Mr = 180,000) of the protein kinase under study was established to have the stoichiometry of R2C2 type under native conditions.

Adenosine 3',5'-monophosphate-dependent protein kinase from normal human adrenal

The protein kinase of normal human adrenal cytosol has been resolved by DEAE-cellulose chromatography into two major components, the protein kinases I and II, which are both adenosine 3',5'-monophosphate (cAMP) dependent. Both enzymes have similar substrate specificities, cAMP-dependency, and sensitivity to the stimulation by this nucleotide, but differ in their states of activation after preincubation with histone. The DEAE--cellulose charomatography of dissociated cytosol protein kinase reveals only one peak of kinase activity and two peaks of cAMP binding activity (A and B). Both binding proteins are able to inhibit the kinase activity of the catalytic subunit. Recombination experiments suggest that the regulatory subunit A originated from protein kinase I and subunit B from protein kinase II. The phosphorylation of histone by adrenal protein kinases is inhibited by a heat-stable protein inhibitor isolated from human fetal brain and human adult adrenal.

The phosphorylation of brain microtubular proteins in situ and in vitro

The phosphorylation of microtubular proteins isolated by reassembly in vitro from slices of guinea-pig cerebral cortex labelled with [32P]orthophosphate was investigated. Under the conditions tested, both and the alpha and beta forms of tubulin contained metabolically-active P which accounted for about one third of the total 32P incorporated into protein; the remaining protein-bound 32P was associated with 3-4 minor high MW components co-purifying with tubulin during two cycles of assembly-disassembly. Microtubular protein prepared in this way contained approx. 0.8 mol of alkalilabile P/mol of tubulin dimer (M.W. 110,000). In vitro studies showed that reassembled microtubular protein preparations catalysed the incorporation of up to 0.55 mol of P/mol of tubulin dimer during incubation with Mg2+ and [gamma 32P]ATP. The reaction was linear during the first 30 min of incubation at 37 degrees C. Cyclic AMP (10 microM, final concentration) caused a transient increase in the initial rates of tubulin phosphorylation. Little label was incorporated into the minor high M.W. components under these conditions. The in vitro phosphorylation of microtubular protein increased in a non-linear manner with respect to protein concentration: this was in contrast to earlier experiments showing linear kinetics when chromatographically isolated tubulin was tested for intrinsic kinase activity. Isolated microtubular protein preparations bound [3H]GTP, [3H]ATP and to a lesser extent, [3H]cyclic AMP, and exhibited Ca(2+)-ATPase activity (up to 60 pmol Pi released min/mg protein at 37 degrees C).

An analysis of the autophosphorylation of rabbit and human erythrocyte membranes

The autophosphorylation of rabbit and human erythrocyte membranes has been studied under various experimental conditions. The phosphopeptides of the erythocyte membranes were identified using sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis followed by ratioautography. The pattern of phosphorylatiion of membrane components differs with respect to the phosphoryl donor used (ATP or GTP) and to the pH at which the reaction is carried out. Both species appear to contain at least two distinct membrane-bound protein kinases. The human erythrocyte membrane contains a cyclic adenosine 3'5'-monophosphate (cyclic AMP)-dependent protein kinase and several substrates for this kinase. Only ATP can be used as a phosphoryl donor for this kinase. In contrast, the rabbit erythrocyte membrane does not contain a cyclic AMP dependent protein kinase but does contain a kinase which utilizes only ATP as the phosphoryl donor and is specific for certain endogenous substrates at low pH. Both the human and rabbit erythrocyte membranes contain a kinase which utilizes GTP, perhaps also ATP, as the phosphoryl donor. The substrates of these kinases are similar in both species.

An adenosine 3':5' monophosphate dependent protein kinase from sea urchin spermatozoa

A cyclic AMP dependent protein kinase (EC 2.7.1.37) from sea urchin sperm as purified to near homogeneity and characterized. A 68-fold purification of the enzyme was obtained. This preparation had a specific activity of 389 000 units/mg protein with protamine as the substrate. On the basis of the purification required, it may be calculated that the protein kinase constitutes as much as 1.5% of the soluble protein in sperm. There appeared to be a single form of the enzyme in sea urchin sperm, based on the behavior of the enzyme during DEAE-cellulose and Sephadex G-200 column chromatography. Magnesium ion was required for enzyme activity. The rate of phosphorylation of protamine was stimulated 2.5-fold by an optimal concentration of 0.9 M NaCl. The Km for ATP (minus cyclic AMP) was 0.119 +/- 0.013 (S.D.) and 0.055 mM +/- 0.009 (S.D.) in the presence of cyclic AMP. The specificity of the enzyme toward protein acceptors, in decreasing order of phosphorylation, was found to be histone f1 protamine, histone f2b, histone f3 and histone f2a; casein and phosvitin were not phosphorylated. The holoenzyme was found to have an apparent molecular weight of 230 000 by Sephadex G-200 chromatography. In the presence of 5 - 10(-6) M cyclic AMP, the holoenzyme was dissociated on Sephadex G-200 to a regulatory subunit of molecular weight 165 000 and a catalytic subunit of Mr 73 000. The dissociation could also be demonstrated by disc gel electrophoresis in the presence and absence of cyclic AMP.

Characterization of protein kinases from bovine parotid glands. The effect of tolbutamide and its derivative on these partially purified enzymes

1. Four fractions of protein kinase (EC 2.7.1.37) activity (Peak IH, IIH, IIIC and IVC) have been resolved and partially purified from the 100 000 X g supernatant fraction of bovine parotid glands by DEAE-cellulose and phosphocellulose chromatographies. 2. The protein kinases of Peak IH and IIH were adenosine 3',5'-monophosphate (cyclic AMP) -dependent and had similar enzymic properties. The enzyme activities of Peak IIIC and IVC were cyclic-AMP independent, but there were some distinct differences between their properties. The protein kinase in Peak IIIC was activated by 0.2 M NaCl or KCl and phosphorylated casein preferentially as the substrate, utilizing only ATP as a phosphate donor. On the other hand, the protein kinase in Peak IVC was inhibited by univalent salts and preferred phosvitin to casein, utilizing either ATP or GTP as a phosphate donor. 3. Tolbutamide increased the Km value for ATP and the dissociation constant for cyclic AMP, resulting in the inhibition of cyclic-AMP dependent protein kinase activity in the presence of cyclic AMP. Tolbtamide and its carboxy derivative, 1-butyl-3-p-carboxyphenylsulfonylurea, exerted almost no inhibitory effect on either the cyclic-AMP dependent protein kinase activities in the absence of cyclic AMP or on the cyclic-AMP independent protein kinase activities.

Cyclic AMP-dependent protein kinases and binding sites for cyclic AMP in rat erythrocytes

In red cell preparations from reticulocyte-poor (untreated animals; approximately 2% reticulocytes) and reticulocyte-rich blood (animals pretreated with acetylphenylhydrazide; approximately 60% reticulocytes) of rats, cAMP binding sites and cAMP-dependent protein kinase activities were determined. High affinity binding sites for cAMP were present both in membrane and cytoplasmic preparations; while the apparent binding constants determined in both cell fractions (approximately 3 x 10(-9) M for membrane, approximately 2 x 10(-8) M for cytoplasmic fractions) were independent of the reticulocyte content of the preparations, the respective numbers of sites were about twice as high in the reticulocyte-rich as in the reticulocyte-poor preparations. In membrane preparations, significant cAMP-dependent protein kinase activity could be detected only in membrane fractions from reticulocyte-rich blood which were considerably contaminated by intracellular components ("haemoglobin-containing membranes') while in washed ("haemoglobin-free') membranes no cAMP-dependent protein kinase activity was found. In cytoplasmic preparations both from reticulocyte-poor and reticulocyte-rich blood, two different protein kinases, a low and a high Ka enzyme, were tentatively differentiated by kinetic data; the apparent activation constant for the high Ka enzyme (approximately less than 5 x 10(-8) M) was in the concentration range of the binding constants determined on cytoplasmic preparations. The activity of the high Ka protein kinase was several fold higher in reticulocyte-rich than in reticulocyte-poor cytoplasmic fractions, while the activity of the low Ka enzyme was obviously independent of the reticulocyte content. From the results obtained, it is concluded that in premature rat erythrocytes, membrane protein(s) may serve as protein substrates for cAMP-dependent protein kinase(s) located in the cytoplasm. This assumption was supported by experiments with intact erythrocytes (prelabelled with inorganic 32P-phosphate) from reticulocyte-rich blood: isoprenaline, theophylline, and also dibutyryl-cAMP significantly increased phosphorylation of membrane protein of these cells. From the results presented (and others previously reported) it becomes evident that only premature rat erythrocytes, i.e. reticulocytes, are equipped with a beta-adrenergic receptor-effector system consisting of a beta-adrenergically stimulated adenyl cyclase and cAMP-dependent protein kinase(s). Obviously, the adrenergic receptor system and also part of the effector system is lost during the process of red cell maturation.

Activation of protein kinase by physiological concentrations of cyclic AMP

When determined under the usual conditions of an excess of ligand over protein, the concentration of cyclic AMP necessary to activate pure preparations of cyclic AMP-dependent protein kinase (EC 2.7.1.37; ATP:-protein protein phosphotransferase) half-maximally is in the range of 0.2-0.3 muM when casein or glycogen synthetase is used as the substrate, i.e., essentially the same as the concentration of the nucleotide that is found in resting skeletal muscle. The apparent dissociation constant for cyclic AMP bound to the protein kinase is also about 0.2-0.3 muM when measured under similar conditions. The concentration of the protein kinase in muscle is relatively high (0.23 muM), however, and under these conditions the apparent activation constant of the enzyme for cyclic AMP is raised so that an increase in cyclic AMP levels in the tissue would cause a concomitant increase in protein kinase activity over a wide range of nucleotide concentration. As a result, it is unnecessary to invoke compartmentalization of cyclic AMP to explain how it can control protein kinase activity in vivo. Another factor that may increase the effectiveness of changes in cyclic AMP concentration is the heat-stable protein inhibitor of protein kinase that may function to inhibit the activity of nearly all the protein kinase catalytic subunit dissociated by basal concentrations of cyclic AMP. Finally, the near equity between the concentration of cyclic AMP binding sites and the ligand itself provides a potential mechanism whereby agents can affect the total cyclic AMP content without directly affecting adenylate cyclase, cyclic AMP phosphodiesterase, or cyclic AMP transport.