Cyclase

About: Cyclase is a research topic. Over the lifetime, 10162 publications have been published within this topic receiving 388566 citations.

Adenyl cyclase in human leukocytes: evidence for activation by separate beta adrenergic and prostaglandin receptors

Abstract: The effects of drugs on adenyl cyclase activity in isolated human leukocytes were examined in two ways: 1) conversion of radioactive adenosine triphosphate to cyclic adenosine monophosphate (AMP) by broken cell preparations; and 2) accumulation of radioactive cyclic AMP within intact leukoytes after preincubation with radioactive adenine. Synthesis of cyclic AMP was increased by prostaglandin-E1(PGE1) and selected catecholamines, but not by glucagon or adrenocorticotropin. Responses to catecholamines were characteristic of a beta adrenergic receptor, both in order of potency or agonists [isoproterenol = epinephrine > norepinephrine > phenylephrine (= 0)] and in being competitively inhibited by beta adrenergic antagonists (propranolol and MJ-1999) but not by alpha antagonists (phentolamine and Dibenamine). The effect of PGE1 was not blocked by propranolol. PGE1 and isoproterenol at maximally effective doses produced no additive effect on cyclic AMP synthesis, suggesting that both drugs stimulate different receptors, but activate the same adenyl cyclase enzyme. The maximum effect of isoproterenol is only about 15% of that produced by PGE1; the possibility that isoproterenol stimulates adenyl cyclase in a fraction of the leukocytes (or specific types of leukocytes) has not been ruled out.

Purification of the calmodulin-sensitive adenylate cyclase from bovine cerebral cortex.

Abstract: A calmodulin-sensitive adenylate cyclase was purified 3000-fold from bovine cerebral cortex using DEAE-Sephacel, calmodulin-Sepharose, and two heptanediamine-Sepharose column steps. The purified enzyme activity was stimulated by calmodulin, forskolin, 5'-guanylyl imidodiphosphate, and NaF. The molecular weight of the protein component was estimated as 328 000 with a smaller form of Mr 153 000 obtained in the presence of Mn2+. The most highly purified preparations contained major polypeptides of 150 000, 47 000, and 35 000 daltons on sodium dodecyl sulfate (SDS) gels. Photoaffinity labeling of the preparation with azido[125I]iodocalmodulin gave one product of 170 000 daltons on SDS gels. It is proposed that the catalytic subunit of the calmodulin-sensitive enzyme is 150 000 +/- 10 000 daltons and that the enzyme exists as a complex of one catalytic subunit and the stimulatory guanyl nucleotide regulatory complex. These data are consistent with the previous report that the catalytic subunit of this enzyme has a molecular weight of 150 000 +/- 10 000 [Andreasen, T.J., Heideman, W., Rosenberg, G.B., & Storm, D.R. (1983) Biochemistry 22,2757].

Modification of the rat adipocyte A1 adenosine receptor-adenylate cyclase system during chronic exposure to an A1 adenosine receptor agonist: alterations in the quantity of GS alpha and Gi alpha are not associated with changes in their mRNAs.

Abstract: The A1-adenosine receptor (A1AR) adenylate cyclase system in rat adipocytes undergoes heterologous desensitization following chronic in vivo exposure to an A1AR agonist (+)-N6-(R-phenylisopropyl)adenosine [J. Biol. Chem. 262:841-847 (1987)]. This desensitization involves an absolute increase in adenylate cyclase activity and a refractoriness to receptor ligands that are inhibitory to adenylate cyclase. In this study, receptor changes were characterized using an A1AR antagonist radioligand, [3H]8-[4-[[[[(2-aminoethyl)amino]carbonyl]methyl] oxy]phenyl]-1,3-dipropyl xanthine. Saturation binding studies demonstrated a 47% decrease in total A1AR density without a change in KD. Agonist competition studies revealed a decreased percentage of receptors, from 55% to 35%, in the high affinity state following desensitization. An increase in GS alpha of 49% was found by Western blotting using specific GS alpha antibodies. Further, an antibody that recognizes Gi alpha 1 adn Gi alpha 2 was used to quantitate these subtypes of Gi alpha and both were decreased by 59% following desensitization. However, when an antibody that recognizes Gi alpha 3 was used, no change in Gi alpha 3 was found, demonstrating, in this case, differential regulation of Gi alpha subtypes. The mechanisms responsible for changes in GS alpha and Gi alpha were studied by measuring the levels of their mRNAs from normal and desensitized adipocytes. Using either labeled cDNAs (Gi alpha 2, Gi alpha 3) or oligonucleotides (GS alpha, Gi alpha 1), Northern analysis demonstrated that mRNAs for GS alpha and all three isoforms of Gi alpha are present in adipocytes but that there are no changes in the levels of any of these transcripts following desensitization. These data suggest that desensitization of the A1AR-adenylate cyclase system involves a down-regulation of A1ARs and an additional loss of A1AR agonist high affinity sites. Further, an increase in GS alpha, a decrease in Gi alpha 1 and Gi alpha 2, and no change in Gi alpha 3 were found. The regulation of GS alpha and the subtypes of Gi alpha in this system does not occur by altering the levels of their respective transcripts.