Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.1 (adenylate cyclase)
 19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fractions enriched in hCG-binding activity were prepared by differential rate centrifugation of superovulated rat ovarian homogenates and were applied to continuous sucrose density gradients (20-55%). After centrifugation at 63,000 x gav for 3.5 h, fractions of each gradient were collected and assayed for a range of marker enzyme activities characteristic of surface membranes and subcellular organelles. Mitochondria, lysosomes, and rough and smooth endoplasmic reticulum membranes accumulated in the gradient between 38-41% sucrose (1.165-1.180 g/cm3). Nuclei passed through the gradient. However, the various surface membrane markers concentrated in two distinct regions of the gradient. Alkaline phosphatase, phosphodiesterase, (Na+ + K+)ATPase I, and hCG-binding activity concentrated at 29-32% sucrose (1.120-1.135 g/cm3), whereas 5'-nucleotidase, Mg2+-dependent ATPase, and adenylate cyclase activities (and minor peaks of hCG-binding and phosphodiesterase activities) were enriched at 36-38% sucrose (1.16-1.17 g/cm3). A second ATPase, [(Na+ + K+)ATPase II], was also observed in this region of the gradient, which could be distinguished from (Na+ + K+)ATPase I of the light membrane fraction by its sensitivity to the Ca2+-chelating agent, ethylene glycol bis-(aminoethyl)tetraacetic acid (EGTA). The kinetics of binding of radioiodinated hCG to the gonadotropin receptors of the light and heavy membrane fractions were very similar. It is suggested that fractionation of superovulated rat ovaries yields two distinct populations of surface membrane material which have distinct densities and marker enzyme profiles. Furthermore, in contrast to the heavy membrane fraction, light membranes seem to possess considerable amounts of hCG receptor activity but very little adenylate cyclase.
 ...
PMID:Interactions of gonadotropins with corpus luteum membranes. II. The identification of two distinct surface membrane fractions from superovulated rat ovaries. 21 57

The influence of behaviorally active, N-terminal fragments of ACTH on the accumulation of cAMP in rat brain investigated in broken cell preparations of subcortical tissue, in slices of neostriatum and in vivo. ACTH1--24 has a biphasic effect on the activity of adenylate cyclase in broken cell preparations of rat brain subcortical tissue: concentrations below 25 micrometer stimulated, whereas concentrations of 0.1 mM and higher inhibited adenylate cyclase activity. The magnitude of the stimulation was dependent on the concentrations of ATP and Mg2+ in the incubation medium. Structure activity studies revealed that at a concentration of 10(-4) M ACTH1--16-NH2 and ACTH4--7 also inhibited the activity of adenylate cyclase, whereas ACTH11--24, ACTH1--10, ACTH4--10, [D-Phe7]ACTH1--10 and [D-Phe7]ACTH4--10 were inactive in this respect. Addition of 0.8 mM EGTA but not of 0.25 mM Ca2+ prevented the inhibition by 10(-4) M ACTH1--24. GMP-N-P (10(-5) M), naltrexone (10(-3) M) and ergometrine (10(-3) M) did not influence the inhibitory effect. ACTH1--24 enhanced the accumulation of cAMP in slices from rat brain neostriatum in a dose-dependent manner. This effect was already maximal 7.5 min after the addition of the peptide and was potentiated by isobutylmethylxanthine, a potent inhibitor or phosphodiesterase. Intraventricular injection of 1 microgram ACTH1--16-NH2 in rats significantly elevated (+ 27%) the concentration of cAMP in the septal region 60 min after the injection of the peptide. The results are discussed in terms of a possible involvement of cAMP as a second messenger in the central nervous system for N-terminal fragments of ACTH.
 ...
PMID:ACTH-like neurotropic peptides: possible regulators of rat brain cyclic AMP. 21 39

Cell surface membrane fragments were isolated and purified by successive rate zonal and isopycnic centrifugation of calcium oxalate-loaded pigeon heart microsomes in sucrose density gradients. The most highly purified cell membrane fraction sediments at a buoyant density of 1.105 g/ml. Some of the membrane pieces are present as open fragments and leaky vesicles, while others form tightly sealed vesicles of both inside-in and inside-out membrane orientation. The pigeon heart cell membrane preparation exhibits high (Na+ + K+ + Mg2+)-ATPase and adenylate cyclase activities. Additional activity of these enzymes is uncovered by sodium dodecyl sulfate and alamethicin, respectively. Electron microscopic inspection of the cell surface membrane preparation revealed (a) a predominance of thick-walled vesicles with smooth surfaces on negative staining and (b) binding of concanavalin A to the bulk of isolated membrane pieces following their incubation with the lectin.
 ...
PMID:Mass isolation of cell surface membrane fragments from pigeon heart. 22 Oct 21

Adenylate cyclase activity and endogenous cyclic AMP levels were measured using a highly sensitive radioimmunoassay and protein binding assay during 24 h of development of Dictyostelium discoideum. Adenylate cyclase activity was not detected until the aggregation stage of development (10 h) when a sudden peak of activity was found. The enzyme was active at all subsequent stages, although a slow decline in activity was observed. Similarly, cyclic AMP levels were not detectable through the first 7 h of development and then showed a sudden peak at aggregation. Following aggregation the cyclic AMP levels decreased to approximately 1/2 the peak value and maintained that level throughout the remainder of the developmental cycle. Adenylate cyclase had a narrow range of substrate saturation with a maximum velocity at 1 to 4 mM ATP at both the aggregation stage (10 h) and the sorocarp stage (24 h). At levels of ATP higher than 6 mM the enzyme from both stages was strongly inhibited. No activity was observed in the absence of Mg2+ or dithiothreitol. The activity from 10-, 14-, and 20-h stages was found bound to a 25,000 x g pellet fraction. The sudden appearance of adenylate cyclase and its product cyclic AMP at aggregation provides additional evidence of a role for this nucleotide in chemotaxis, and the retention of enzyme activity and nucleotide level during the subsequent stages may reflect a further function of cyclic AMP during formation of the two cell types.
 ...
PMID:Adenylate cyclase activity and cyclic AMP levels during the development of Dictyostelium discoideum. 22 25

Escherichia coli heat-labile enterotoxin was synthesized in a cell-free system directed by DNA of the plasmid P307. Synthesis of the toxin, assayed by the elongation induced in Chinese hamster ovary cells, was strongly stimulated by cyclic AMP and occurred at physiological levels of Mg2+ only when the polyamine spermidine was present. Activity was abolished by heat and antisera prepared against the enterotoxins of both E. coli P263 and Vibrio cholera. Tritium-labeled enterotoxin was purified by immunoprecipitation and examined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. When gel slices were assayed for the ability to stimulate adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity in erythrocyte ghosts, two peaks were found, one at Mr 26,000 and frequently, but not always, another at Mr 23,000. Detection of radiolabeled protein by fluorography and scintillation counting of gel slices revealed three prominent polypeptides, two corresponding to the peaks having adenylate cyclase-stimulating activity and a further one of Mr 11,500, identical to that of the cholera subunit B. The data suggest that the E. coli heat-labile enterotoxin synthesized in the cell-free system has a subunit structure.
 ...
PMID:Escherichia coli heat-labile enterotoxin: DNA-directed in vitro synthesis and structure. 22 67

A large number of hormones and neurotransmitters activate adenylyl cyclase [ATP, pyrophosphate lyase (cyclizing; EC 4.6.1.1.)] catalyzing the formation of cAMP and PPi from ATP in the presence of Mg2+. The cAMP formed is in turn responsible for eliciting the physiological responses of these hormones and neurotransmitters. In addition to hormones and neurotransmitters, fluoride ion, cholera toxin and guanyl nucleotides (GTP and GTP analogs such as GTP gamma S and GMP-P(NH)P) also stimulate adenylyl cyclase activity (Perkins, 1974; Birnbaumer, 1977; Gill, 1977). It has become evident that hormonally-responsive adenylyl cyclase is a multi-component system consisting of at least 3 physically distinct units. The first is the hormone receptor containing a specific site for a given hormone. The second is the catalytic moiety (C component) of adenylyl cyclase bearing the site responsible for catalysis of the cyclizing reaction. The third is the guanyl nucleotide regulatory subunit (G component) which binds guanyl nucleotide. Recently, a GTPase activity has been found to be associated with the G component of adenylyl cyclase (Cassel and Selinger, 1976; Cassel et al., 1977a, b; Lambert et al., 1979). In this review we will present information on the regulation of hormonally-responsive adenylyl cyclases. This is not intended to be a comprehensive review of the literature. Rather, it represents our views on the current status of the regulation of cAMP formation.
 ...
PMID:Guanyl nucleotide regulation of hormonally-responsive adenylyl cyclases. 23 Jan 2

The kinetic characteristics of substrate utilization by hepatic adenylate cyclase were investigated under a variety of incubation conditions, including veriations in pH, [substrate], [Mg2+], and in the absence or presence of glucagon. Activities were compared with ATP and 5'-adenylylimidodiphosphate (App(NH)p) as substrates. The Km for both substrates was about 50 muM; Vmax given with App(NH)p was about 40% lower than obtained with ATP as substrate. In the presence of a saturating concentration of substrate (1 mM), basal activity was increased 4-fold by increasing [Mg2+] from 5 to 50 mM. The stimulatory effect of Mg2+ was not due to an allosteric action since basal activity was only marginally enhanced (40%) when the substrate concentration was reduced to 10 muM. As suggested by deHaen ((1974 J. Biol. Chem. 249, 2756), it is likely that Mg2+ increases enzyme activity by decreasing the concentration of an inhibitory, unchelated form of substrate that competes with the productive magnesium-substrate complex at the active site. Activity-pH profiles differed with ATP and App(NH)p as substrates; a shift in pH optimum was observed which correlated with the different pKa of the terminal phosphate groups of ATP and App(nh)p, and which reflect the concentration of protonated substrate (ATPH-3 minus) present in the incubation medium. Accordingly, protonated substrate is the predominant inhibitory species of unchelated substrate and probably has a considerably higher affinity for the active site than does the magnesium-substrate complex. Glucagon-stimulated activity was less susceptible to inhibition by protonated substrate than is the basal state as evidenced by lower stimulatory effect when the [Mg2+] was increased from 5 to 20 mM. However, increasing the [Mg2+] from 20 to 50 mM resulted in marked inhibition of glucagon-stimulated activity, particularly in the presence of 10 muM substrate. Conversely, at a fixed [Mg2+], concentrations of substrate at least 20-fold higher than the Km were required to achieve maximal hormone-stimulated activity. These findings suggest that the unchelated, fully ionized form of substrate serves as an activating ligand, as has been observed with guanine nucleotides at considerably lower concentrations. Thus, Mg2+ affects adenylate cyclase activity by forming the productive substrate complex and by titrating the inhibitory protonated and activating free forms of substrate. As a result of these effects of unchelated substrate, it proved difficult to evaluate the kinetic parameters involved in substrate binding and utilization and the effects of hormone thereon when substrate was added as the only source of activating ligand. However, linear Michaelis kinetic data were obtained by adding the activating ligand 5'-guanylylimidodiphosphate with glucagon and by making appropriate adjustments of pH and [Mg2+]. Vmax was increased 4-fold without changes in Km by the actions of 5'-guanylylimidodiphosphate and glucagon.
 ...
PMID:The hepatic adenylate cyclase system. II. Substrate binding and utilization and the effects of magnesium ion and pH. 23 15

Guanylate cyclase has been purified from extracts of Escherichia coli. After a 1000-fold purification, the enzyme contains only minor contaminants as judged by disc gel electrophoresis. The Km for GTP is approximately 7 times 10(-5) M and the optimal pH is 8.0. More activity is observed with Mn2+ than with Mg2+, and maximal activity is observed at 0.14 mM Mn2+ and 1.4 mM Mg2+. Based on its behavior on Sephadex G-100, the molecular weight of E. coli guanylate cyclase is about 30,000. Disc gel electrophoretic analysis indicates that the enzyme consists of a single polypeptide chain. Guanylate cyclase does not form 3':5'-AMP from ATP, and therefore, is distinct from adenylate cyclase.
 ...
PMID:Guanylate cyclase in Escherichia coli. Purification and properties. 23 41

Histamine and epinephrine stimulate the activity of guinea pig heart adenylate cyclase [ATP pyrophosphate-lyase (cyclizing) EC 4.6.1.1], in part, by decreasing the requirement for Mg2+ as an activator. This effect may represent an increase in affinity for Mg2+ and/or a decrease in sensitivity of the enzyme towards inhibition by free ATP. Both of these inotropic hormones also increase maximum velocity. Pretreatment of the membrane-bound enzyme with EDTA, to remove available divalent cations, almost eliminates persistent stimulation by guanyl-5'-yl imidodiphosphate [Gpp(NH)p]. Addition of Mg2+ to the preincubation medium restores the capacity of Gpp(NH)p to acutely activate the enzyme. These results indicate that Mg2+ interacts with the nucleotide (GTP) regulatory site. Persistent stimulation of the enzyme by either Gpp(NH)p or fluoride ion also involves a decrease in the requirement for Mg2+ and an increase in maximum velocity.
 ...
PMID:Activation of cardiac adenylate cyclase: horminal modification of the magnesium ion requirement. 26 97

Previous studies have indicated that rat luteal cells at certain stages of development can be fractionated so as to obtain two plasma membrane fractions with different densities and different profiles of marker enzymes. The light membrane fractions (density 1.13) contain the majority of hCG-binding sites and little or no cyclase enzyme, while the heavy membranes (density 1.17) contain the majority of cyclase enzyme and lesser quantities of hormone-binding sites. These membrane fractions were further compared with respect to their susceptibility to perturbation by digitonin. The buoyant density of luteal cell light membrane fractions, as marked by [125I]iodo-hCG binding, Mg2+-dependent ATPase, and 5'-nucleotidase, were highly perturbable by digotonin (delta density, greater than 0.05), while adenylate cyclase activity and phosphodiesterase activity associated with this fraction were only slightly perturbed (delta density, less than 0.02). The buoyant density of luteal cell heavy membrane fractions, as marked by adenylate cyclase, ATPase, and nucleotidase, was not significantly perturbed by digotonin. The hCG binding associated with the heavy membrane fraction was not perturbed by digitonin. From these studies, we conclude that the adenylate cyclase activity associated with light membrane fractions is due to contamination by heavy membranes, while the hCG-binding activity in heavy membrane fractions is intrinsic to that membrane. Except for the lysosomal marker (glucuronidase), which was solubilized by digitonin, the detergent had no significant effect on the density of mitochondrial, Golgi, GERL (Golgi, endoplasmic reticulum, and lysomal), or endoplasmic reticulum membranes. Plasma membranes from isolated granulosa cells and ovaries obtained 24 h after priming with PMS gonadotropin-hCG behaved as heavy membranes (density, 1.17) which contained hCG-binding sites, adenylate cyclase, nucleotidase, and Mg2+-dependent ATPase. These were not significantly perturbed by digitonin. The appearance of light membranes and the segregation of adenylate cyclase from the majority of hCG-binding sites is a development feature of the luteal cell.
 ...
PMID:Interactions of gonadotropins with corpus luteum surface membranes. V. Differential effects of digitonin on the buoyant densities of light and heavy rat ovarian membrane fractions. 43 71


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>