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)

Continued exposure of many beta-adrenoceptor-coupled adenylate cyclase systems to high doses of agonist causes diminished responsiveness, a phenomenon called desensitization. After exposure of isolated guinea pig tracheae to a high concentration of isoproterenol for 30 min, relaxation produced by subsequent challenge by a lower concentration was attenuated, as expected. However, potentiation of isoproterenol-induced relaxation by aminophylline was greater after desensitization as compared to that prior to desensitization. This observation was further investigated using a graphical method that allows quantitative and statistical evaluation of combinations of synergistically acting drugs. Concentration-relaxation curves (CRC) for isoproterenol alone and in the presence of a fixed concentration of aminophylline were determined in isolated rat trachea. A theoretical additive curve was constructed from the data obtained, and the displacement of the isoproterenol CRC from the theoretical additive curve caused by aminophylline in tracheae desensitized by 2.5 hr of exposure to 2 X 10(-5) M isoproterenol (DESN) was compared to that in tracheae equilibrated for a similar period in physiologic salt solution (CON). Desensitization had no significant effect on aminophylline-induced relaxation but caused a marked depression and right-shift of the isoproterenol CRC. In the CON group aminophylline shifted the isoproterenol CRC upward and to the left indicating that the synergistic interaction between the two agents was greater than additive. The left-shift and elevation of the ceiling effect of the isoproterenol CRC caused by aminophylline were significantly greater in the DESN group vs the CON group. These observations from intact tissue are compared with published data from biochemical and broken cell studies. The possibility of increased phosphodiesterase activity as an explanation for the observations reported is discussed.
 ...
PMID:Potentiation of isoproterenol-induced relaxation of isolated trachea by aminophylline: modulation by desensitization. 361 5

We previously reported the activation of adenylate cyclases from rat brain (Johnson, R. A., Awad, J. A., Jakobs, K. H., and Schultz, G., (1983) FEBS Lett. 152, 11-16) and from human platelets (Jakobs, K. H., Johnson, R. A., and Schultz, G. (1983) Biochim. Biophys. Acta 756, 369-375) by a factor derived from bovine sperm. In this report we describe the conditions for the extraction of the factor from bovine sperm and characteristics of its effects on adenylate cyclase which are consistent with its being a protease. The activating capacity of sperm particles was extracted from previously washed and frozen sperm into a 30,000 X g supernatant fraction by various salts, but not by the nonionic detergent Lubrol-PX. The amount of extracted factor: (a) was greatest with NH4HCO3 greater than NaCl greater than Na acetate; (b) was optimal with 0.5 M salt; (c) was not appreciably affected by the pH of the extraction buffer between pH 5.0 and 8.5; and (d) exhibited the greatest specific activity at the lower pH. The extracted sperm factor could be concentrated without loss by ultrafiltration on Amicon PM-10 membranes. The effect on adenylate cyclase of concentrated and desalted sperm extracted was inhibited 50% by various salts at 10 to 30 mM. The effects of the sperm factor to activate platelet adenylate cyclase, to block its inhibition via the alpha-adrenoceptor, and to block inhibition of stimulated forms of the enzyme by stable guanine nucleotides were prevented by protease inhibitors. A 50% reduction in the sperm factor's activation of platelet adenylate cyclase was caused by 30 nM soybean trypsin inhibitor, 30 nM alpha 2-macroglobulin, 300 nM leupeptin, 1 microM antipain, 15 microM aprotinin, and 100 microM benzamidine. Up to 3 mM phenylmethanesulfonyl fluoride was without effect on activation of the platelet cyclase by the sperm factor. The effects of the sperm factor persisted after its removal by the washing of pretreated platelet membranes and after its inactivation by the subsequent addition of leupeptin. The data strongly support the conclusion that the bovine sperm factor is a trypsin-like protease. alpha-Chymotrypsin, trypsin, and sperm acrosin were comparably effective in stimulating the platelet adenylate cyclase 5- to 8-fold, with concentrations eliciting maximal stimulation being: 200 ng trypsin/ml; 2 micrograms alpha-chymotrypsin/ml; and 2 micrograms acrosin/ml.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Extraction of the adenylate cyclase-activating factor of bovine sperm and its identification as a trypsin-like protease. 388 Jul 36

Interactions of several divalent cations (Mn2+, Ca2+, Co2+, Sr2+, and Zn2+) with EGTA-inhibitable adenylate cyclase were investigated in washed membranes (particles) isolated from the gray matter of rat cerebral cortex. The EGTA-inhibitable (called sensitive) enzyme activity was assayed in the presence of Triton X-100 since this detergent caused a marked increase (up to 20-fold) in the enzyme activity. The effects of various divalent metals (all added as chloride salt) indicated the presence of two distinct sites called site I and site II. At low concentrations (less than micromolar) Mn2+, Co2+, and Ca2+ increased (up to 10-fold) the enzyme activity to the same extent and appeared to act via binding to site I (high affinity site). The rank order of affinity was Mn2+ greater than or equal to Co2+ greater than Ca2+. Zn2+ showed the highest affinity and Sr2+ the lowest towards binding to site I; both these metals increased the enzyme activity to lesser extents than Mn2+, Co2+, or Ca2+. GTP was not required for the stimulation of this enzyme by low concentrations of Ca2+. The interaction of Mn2+ with site II (low affinity site) caused further increase in the enzyme activity, whereas Co2+, Ca2+, and Sr2+ were inhibitory at concentrations greater than 10 microM. Isolated fraction contained loosely and tightly associated pools of calmodulin. Myelin basic protein, but not calcineurin, inhibited the EGTA-sensitive adenylate cyclase activity. The EGTA-insensitive enzyme activity was increased by norepinephrine by mechanisms that depended on GTP and was inhibited by Ca2+. The stimulation of the EGTA-insensitive enzyme modulated the Mg2+ requirement such that Mg2+ binding to the low affinity site (site II) apparently occurred with higher affinity. The likely significance of these results is discussed with regard to (i) the presence of two classes of adenylate cyclase in rat cerebral cortex gray matter and (ii) the regulation of their activities by calmodulin-requiring and GTP-requiring mechanisms.
 ...
PMID:EGTA-sensitive and -insensitive forms of particulate adenylate cyclase in rat cerebral cortex: regulation by divalent cations and GTP. 393 3

1. Intracellular recordings of membrane potential were made from superficial cells of isolated mouse liver segments superfused with physiological salt solutions.2. The mean resting cell membrane potential was -39.4 mV.3. Glucagon caused a dose-dependent membrane hyperpolarization which was detectable at 10(-9)M and maximal (7 mV) at 10(-7)M. The hyperpolarization started within half a minute after exposure to glucagon. Secretion (2 x 10(-7)M) had no effect on the membrane potential.4. Adrenaline (10(-6)M) and isoprenaline (10(-6)M) also caused membrane hyperpolarization (4-6 mV). The effect of isoprenaline, but not that of adrenaline, was blocked by propranolol (5 x 10(-6)M).5. Dibutyryl adenosine 3',5'-monophosphate (10(-3)M) caused a membrane hyperpolarization of 4-8 mV.6. In the absence of extracellular K or the presence of Strophanthin-G (10(-3)M) the resting potential was decreased and the response to glucagon reduced. During exposure to a solution containing 20 mM-K the resting potential was slightly enhanced and the amplitude of the glucagon-induced hyperpolarization reduced compared with control conditions.7. It is concluded that the effect of glucagon on the membrane potential is due to an interaction with specific membrane receptors probably leading to activation of the membrane-bound adenyl cyclase. It is probable that the hyperpolarization is mediated by cyclic AMP. The hyperpolarization induced by glucagon is dependent on a normal function of the membrane Na-K pump.
 ...
PMID:The effect of glucagon on the liver cell membrane potential. 436 92

The catalytic subunit of rat brain adenylate cyclase was separated from its stimulatory subunit with loss of activation by 5'-guanylylimidodiphosphate. With respect to other properties, the resolved catalytic subunit was similar to the native enzyme. Nucleotide activation was restored after reconstitution with the isolated regulatory subunit. A key step in resolution was preliminary exposure of isolated membranes to increased ionic strength. After solubilization with nonionic detergent solution, the subunits were separated by gel filtration. The apparent molecular size of the catalytic subunit was unchanged by salt treatment, whereas the Stokes' radius of the regulatory subunit decreased from 72 A to 48 A.
 ...
PMID:Separation of the catalytic and stimulatory regulatory subunits of rat brain adenylate cyclase. 608 5

A cytochemical procedure for the localization of adenylate cyclase with Sr2+ as the capture ion and adenylyl imidodiphosphate as the specific substrate was evaluated in the rat pancreas. Incubation medium was unaffected by the addition of 5 mM strontium ions but became turbid in the presence of lead or strontium plus 10 mM NaF. Tissues were prefixed in 2% formaldehyde/0.5% glutaraldehyde and incubated, and the cytochemical precipitate was converted to the Pb2+ salt. Enzymatic activity was demonstrated on the plasma membrane of pancreatic acinar cells and responded to stimulation by secretin. Controls frequently contained Pb2+ sequestered in mitochondria, but otherwise only a few randomly distributed grains were observed. The controls were 1) omission of substrate from the medium; 2) incubation of tissue for 1 min in complete medium; and 3) tissue previously inactivated by microwave irradiation and incubated for 30 min in complete medium including secretin.
 ...
PMID:Cytochemical demonstration of adenylate cyclase with strontium chloride in the rat pancreas. 618

Cell culture, a powerful tool for the study of cell biology, offers advantages for the study of renal cell function. Epithelial cells derived from a variety of organs, including the kidney, form oriented epithelial sheets in culture that have many structural characteristics (microvilli, tight junctions) of epithelia in situ. There is evidence of transepithelial transport of salt and water by cells of two lines (MDCK and LLC-PK1) derived from mammalian kidney. LLC-PK1 cells may also manifest the glucose transport system of the proximal tubule. Cells of both lines have adenylate cyclase activity sensitive to hormones. Two lines of cells derived from toad urinary bladder form epithelia with a high transepithelial resistance and transport sodium actively from apical to basolateral surface. The rate of sodium transport in both lines is stimulated by cyclic AMP and by aldosterone. There are important differences in the characteristics of the response of the two lines to aldosterone as well as in their sensitivity to inhibition of sodium transport by amiloride. These differences may lead to new insights regarding the molecular events in the response to aldosterone and in the inhibitory action of amiloride. Cultures of kidney cells have also been used effectively to study the biosynthesis of the hormonal derivative of vitamin D and to study prostaglandin production. In addition, cell culture is ideally suited for study of the developmental biology of the kidney.
 ...
PMID:Studies of renal cell function using cell culture techniques. 624 76

A rat heart sarcolemmal preparation could be obtained in which both 5'-nucleotidase and adenylate cyclase were enriched approx. 9-fold by subjecting a homogenate to a discontinuous sucrose gradient, without the use of a high salt extraction. After incubation of this fraction with Mg[gamma-32P]ATP, the majority of 32P incorporated was present in 24 000- and 9000-dalton protein components. Only when a heart cytosol fraction or a purified cyclic AMP-dependent protein kinase was added, was enhancement of 32P-incorporaton found by addition of cyclic AMP. The 9000- and 24 000-dalton proteins appeared to be interconvertible. The degree of conversion could be affected by changing the temperature during solubilizaion of the membranes in SDS prior to electrophoresis. This suggested that the 24 000-dalton protein does not correspond to phospholamban, first identified by others in canine heart sarcoplasmic reticulum. Moreover, it could be excluded that the 24 000-dalton protein was derived from contaminating myofibrillar troponin I. When the sarcolemmal fraction was preincubated with Ca2+, Mg2+, ATP and oxalate, contaminating sarcoplasmic reticulum vesicles, loaded with calcium oxalate, settled to a greater density in the sucrose gradient. Membrane constituents other than those with enzymatic activity were monitored to confirm the separation between sarcolemmal and sarcoplasmic reticulum membranes: Coomassie blue staining material, sialic acid, cholesterol and phospholipid. The 24 000- and 9000-dalton proteins were equally distributed among the sarolemmal and sarcoplasmic reticulum fractions present in the sucrose gradient. However, the rate of 32P-incorporation in the presence of heart cytosol fraction was much slowr in the sarcoplasmic reticulum than in the sarcolemmal fraction.
 ...
PMID:Phosphorylation of low molecular weight proteins in purified preparations of rat heart sarcolemma and sarcoplasmic reticulum. 625

A great deal of knowledge has been gained concerning the activation of adenylate and guanylate cyclase in epidermal cells. Adenylate cyclase is activated by 4 different independent receptors-responding respectively to catecholamine (beta), to prostaglandins (E), to histamine (H2), and to adenosine and it phosphorylated derivatives. Upon activation, each of these receptors becomes unresponsive to further stimulation by its specific stimulator. Guanylate cyclase, on the other hand, is activated by histamine (H1) and epidermal growth factor (EGF). Unlike EGF, the histamine activation is extremely rapid (less than 5 minutes). Epidermal cells are permeable (leak) to cyclic GMP but not cyclic AMP. When the skin is traumatized or injured in any way (even by intradermal injection) there is a sudden catastrophic change in the intracellular levels of the cyclic nucleotides (and of ATP). Cyclic AMP rapidly rises to perhaps 5-10 times its normal resting level while cyclic GMP falls to 10-20% of its level in vivo. The rise in cyclic AMP is due to activation of adenylate cyclase while the fall in cyclic GMP is due in major part to activation of cyclic GMP phosphodiesterase (and perhaps the fall in ATP is due to activation of ATPase). The changes in ATP and cyclic AMP can be reversed by incubating the tissue in a buffered salt solution containing glucose, but this does not normalize the cyclic GMP content. The fall in cyclic GMP can be prevented by a phosphodiesterase inhibitor (IBMX ). This series of events has been called the "ischemia effect." However, it implies that a lack of oxygen is at fault, and that has not been shown to be the case. Its underlying cause and possible physiologic significance are not known. Do these changes in cyclic nucleotides have effects on epidermal proliferation? And does EGF? Agents which increase cyclic AMP do inhibit the epidermal outgrowth and mitotic activity of explant cultures of pig skin. Cyclic GMP does increase outgrowth at a particular concentration. Histamine, which elevates both cyclic nucleotides, has a biphasic action depending on its concentration. These findings imply that these nucleotides do act as one of the controls of epidermal proliferation. The action of cyclic GMP is not accompanied by detectably increased phosphorylation of epidermal proteins. On the other hand, EGF action which also enhances epidermal outgrowth is characterized by an increased protein phosphorylation that precedes any increase in cellular cyclic GMP. We conclude that the action of EGF is independent of the cyclic nucleotide system.
 ...
PMID:Cyclic GMP system in the epidermis. 626 50

The effects of GTP on adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] of human and rat fat cell membranes ("ghosts" and purified membranes) were examined in the absence and presence of added inorganic salts. With human ghosts GTP alone (0.1 mM) inhibited enzyme activity by 40% at 30 degrees C and had no significant effect at 37 degrees C. At both temperatures Na+ salts of Cl-, N3-, and SO2-(4) stimulated activity (up to 4-fold basal activity for 200 mM NaN3), with maximal effects at salt concentrations of 100-200 mM. Over the same concentration range these salts also allowed temperature-dependent stimulation by GTP. GTP increased the maximal activity produced by salt alone by about 2-fold at 30 degrees C and about 4-fold at 37 degrees C. Na+ (added as Cl-) was much more effective than other alkali metal cations in promoting activation by GTP. Na+ salts allowed activation of the human enzyme by the GTP analog 5'-guanylyl imidodiphosphate and also promoted stimulation of rat fat cell adenylate cyclase by both nucleotides. In time course studies of human and rat fat cell ghosts, GTP appeared to sustain an initial high rate of salt-stimulated activity, which in the absence of nucleotide subsequently fell to a lower rate, suggesting that salts might activate adenylate cyclase by promoting the stimulatory effect of endogenous membrane-bound GTP. However, with purified human fat cell membranes and a GTP-free system, salts were still stimulatory and promoted activation by added GTP. These results differ from those of previous reports in other systems in which Na+ has promoted only inhibitory effects in GTP regulation of adenylate cyclase.
 ...
PMID:Salts promote activation of fat cell adenylate cyclase by GTP: special role for sodium ion. 627 72


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