Properties of detergent-dispersed myocardial adenylate cyclase

Stimulatory and inhibitory regulation of myocardial adenylate cyclase by 5'-guanylyl-imidodiphosphate

Particulate and soluble rat myocardial adenylate cyclase enzymes were characterized with respect to their stimulatory and inhibitory regulation by Gpp(NH)p. Gpp(NH)p (60 microM) stimulated Mg2+- and Mn2+-dependent adenylate cyclase. High concentrations of Gpp(NH)p (600 microM) attenuated the maximal stimulatory response to Gpp(NH)p but only at low cation concentrations. The attenuating effects of 600 microM Gpp(NH)p resulted predominantly from the introduction of a prolonged lag in the kinetics of activation of adenylate cyclase. Steady-state rates of adenylate cyclase activities were similar with either 60 or 600 microM Gpp(NH)p. At any concentration of Gpp(NH)p, the lag was eliminated by Mg ions or isoproterenol. No antihysteretic property for free Mn ions was evident. Forskolin-sensitive particulate adenylate cyclase was not stimulated further by Gpp(NH)p. A 600 microM concentration of Gpp(NH)p inhibited particulate forskolin-sensitive adenylate cyclase at low Mg ion concentrations. In contrast, Gpp(NH)p at 60 microM consistently activated forskolin-sensitive adenylate cyclase after solubilization. The early transient inhibitory properties of 600 microM Gpp(NH)p which resulted in attenuation of adenylate cyclase by 600 microM Gpp(NH)p were diminished by detergent extraction, resulting in only a minor effect of 600 microM Gpp(NH)p to inhibit solubilized adenylate cyclase. These findings indicate that guanine nucleotides exert both stimulatory and inhibitory control upon the myocardial adenylate cyclase enzyme; that solubilization shifts the balance between the stimulatory and inhibitory properties of Gpp(NH)p to allow more dominant expression of the stimulatory response; and that Mg ions critically modify the nature of the myocardial adenylate cyclase response to Gpp(NH)p.

The action of six lipid perturbing substances on hormone receptor adenylate cyclase complex in turkey erythrocytes and intestinal mucosa cells

Adenylate cyclase and beta-receptor binding in turkey erythrocytes is studied under the influence of dioctyl sodium sulphosuccinate (DSS), sodium dodecyl sulphate (SDS), sodium deoxycholate (DOC), filipin, oxyphenisatine and ethanol. Intact and lysed erythrocytes and erythrocyte membranes were investigated. In general the fluoride stimulated enzyme was most resistant to the action of the substances followed by the ligand binding, the hormone stimulated enzyme being most sensitive to the action of the substances. However, in certain ranges of concentrations, DSS, SDS, filipin and oxyphenisatine could further stimulate the fluoride stimulated enzyme. The adenylate cyclase in intestinal mucosa cells was studied in the presence of DSS, SDS, DOC and oxyphenisatine. The fluoride stimulated enzyme was here less stable than the basal enzyme activity, and two of the substances (SDS and oxyphenisatine) stimulating the erythrocyte enzyme could not stimulate the fluoride stimulated intestinal mucosa cell enzyme.

Dopamine receptors in canine caudate nucleus

Physiological, pharmacological, histochemical and biochemical studies indicate that dopamine receptors are heterogenous in the central nervous system with each individual functions. This review describes pharmacological and biochemical characteristics of dopamine receptors, particularly in canine caudate nucleus, which have been studied in our laboratory with a brief comparison to the current studies by other workers in similar research fields. Two distinct dopamine receptors have been characterized by means of [3H]dopamine binding to the synaptic membranes from canine caudate nucleus. One of the receptors with a Kd of about 3 muM for dopamine may be associated with adenylate cyclase and referred to as D2 receptor. The other receptor with a Kd of about 10 nM for dopamine is independent of adenylate cyclase and referred to as D2. A photochemical irreversible association of [3H]dopamine with the membraneous receptors makes it possible to separate D1 and D2 receptors from one another by gel filtration on a Sephadex G-200 column after solubilization with Lubrol PX. On the basis of selective inhibition of [3H]dopamine binding to D1 and D2 receptors, dopamine antagonists can be classified into three classes: D1-selective (YM-09151-2), D2-selective (sulpiride) and nonselective (haloperidol, chlorpromazine). Effects of these typical antagonists on the metabolism of rat brain dopamine suggest that D1 receptor is more closely associated with the neuroleptic-induced increase in dopamine turnover. Studies with 28 benzamide derivatives and some classical neuroleptics reveal that apomorphine-induced stereotypy displays a greater association with D1 than with D2 receptors. Dopamine-sensitive adenylate cyclase in canine caudate nucleus can be solubilized with Lubrol PX in a sensitive form to either dopamine. Gpp(NH)p or fluoride Sephadex G-200 gel filtration separates adenylate cyclase from D1 receptors with a concomitant loss of dopamine sensitivity. Addition of the D1 receptor fraction to the adenylate cyclase restores the responsiveness to dopamine. The solubilized dopamine-unresponsive adenylate cyclase can be further separated into two distinct fractions by a batch-wise treatment with GTP-sepharose: a catalytic unit which does not respond to fluoride, and a guanine nucleotide regulatory protein. The regulatory protein confers distinct responsiveness to Gpp(NH)p and fluoride upon adenylate cyclase. These results indicate that dopamine-sensitive adenylate cyclase is composed of at least three distinct units; D1 receptor, guanine nucleotide regulatory protein and adenylate cyclase.

Characterization of adenylate cyclase purified from rat brain by hydrophobic chromatography

Hydrophobic chromatography of detergent-solubilized rat brain adenylate cyclase on dodecyl-Sepharose produced a species that was soluble in the absence of detergent and could be manipulated like a conventional hydrophilic protein. Sevenfold purification was achieved by this technique. Further purification could then be effected by affinity chromatography on ATP-Sepharose. The purified enzyme was no longer sensitive to fluoride or guanyl nucleotides. No interaction of brain adenylate cyclase was observed with immobilized triazinyl dyes such as Cibacron Blue 3GA nor with con-canavalin A-Sepharose. The molecular weight of the fluoride-activated catalytic complex in a freeze-dried membrane preparation was estimated to be 133,000 by irradiation inactivation.

Catecholamine and guanine nucleotide activation of skeletal muscle adenylate cyclase

Activation of adenylate cyclase by guanine nucleotide and catecholamines was examined in plasma membranes prepared from rabbit skeletal muscle. The GTP analog, 5'-guanylyl imidodiphosphate caused a time and temperature-dependent activation of the enzyme which was persistent, the Ka was 0.05 microM. 5'-Guanylyl imidodiphosphate binding to the membranes was time and temperature dependent, KD 0.07 microM. Beta adrenergic amines accelerated the rate of 5'-guanylyl imidodiphosphate activation of the enzyme with an order of potency isoproterenol approximately soterenol approximately salbutamol greater than epinephrine greater than norephrine. Catecholamine activation was antagonized by propranolol and the beta2 antagonist butoxamine; the beta1 antagonist practolol was inactive. [3H]Dihydroalprenolol bound to the membranes and binding was antagonized by beta adrenergic agonists with an order of potency similar to the activation of adenylate cyclase and was antagonized by butoxamine but not by practolol. The data are consistent with the idea that adenylate cyclase in skeletal muscle plasma membranes is coupled to adrenergic receptors of the beta2 type.