Topic
Cyclase
About: Cyclase is a research topic. Over the lifetime, 10162 publications have been published within this topic receiving 388566 citations.
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TL;DR: It is proposed that the high-affinity binding sites for forskolin are associated with the activated complex of catalytic subunit and stimulatory guanine nucleotide binding protein.
Abstract: [12-3H]Forskolin (27 Ci/mmol) has been used to study binding sites in rat brain tissue by using both centrifugation and filtration assays. The binding isotherm measured in the presence of 5 mM MgCl2 by using the centrifugation assay is described best by a two-site model: Kd1 = 15 nM, Bmax1 (maximal binding) = 270 fmol/mg of protein; Kd2 = 1.1 microM; Bmax2 = 4.2 pmol/mg of protein. Only the high-affinity binding sites are detected when the binding is determined by using a filtration assay; Kd = 26 nM, Bmax = 400 fmol/mg of protein. Analogs of forskolin that do not activate adenylate cyclase (EC 4.6.1.1) do not compete effectively for [3H]forskolin binding sites. Analogs of forskolin that are less potent than forskolin in activating adenylate cyclase are also less potent in competing for forskolin binding sites. The presence of 5 mM MgCl2 or MnCl2 was found to enhance binding. In the presence of 1 mM EDTA the amount of high-affinity binding is reduced to 110 fmol/mg of protein with no change in Kd. There is no effect of CaCl2 (20 mM) or NaCl (100 mM) on the binding. No high-affinity binding can be detected in membranes from ram sperm, which contains an adenylate cyclase that is not activated by forskolin. It is proposed that the high-affinity binding sites for forskolin are associated with the activated complex of catalytic subunit and stimulatory guanine nucleotide binding protein.
111 citations
TL;DR: It is suggested that inhibition and activation of fat cell adenylate cyclase by GTP occur through distinct regulatory processes.
110 citations
TL;DR: It is proposed that GTP enhances adenylate cyclase by altering the interaction between hormone and receptor, and the receptor site specific for the ethanolamine function of the catecholamine molecule is influenced by the nucleotides.
110 citations
TL;DR: It is demonstrated that VIP activates an adenylate cyclase from a synaptosomal fraction of guinea pig brain, and this activation was not potentiated by guanyl triphosphate nucleotides, and was unaffected by α- and β-adrenergic blockers and by atropine.
110 citations
TL;DR: Adenylate cyclase of homogenates or lysates of mouse and rat lymphoid tissues was activated by the addition of fluoride ion, epinephrine, or norepinephrine, but not by any of several other hormones.
Abstract: Adenylate cyclase of homogenates or lysates of mouse and rat lymphoid tissues was activated by the addition of fluoride ion, epinephrine, or norepinephrine, but not by any of several other hormones. The catecholamine stimulation was characterized as β-adrenergic. This activity was localized in the small lymphoid cells, was greater in thymic than in splenic or mesenteric node cells, and also was greater in mouse than in rat cells. Catecholamine-stimulated activity of mouse thymocytes remained constant from the 17-19th day of fetal development to 5 weeks after birth; it subsequently decreased to about one-half of the activity by 7-8 weeks. Similar decreases with age occurred in mouse spleen and rat thymus. In contrast, the glucagon-stimulated activity of rat liver increased during a similar period. Hypophysectomy of rats at 3 weeks did not influence the amount of cyclase activity of thymocytes assayed at 7 weeks.
When intact mouse thymocytes were first incubated in a culture medium at 37°C with epinephrine or norepinephrine, a second addition of catecholamine after cell lysis no longer stimulated the enzymes. This loss of stimulation was selective, since basal activity and stimulation by fluoride ion were not affected. Incubation of intact cells with phytohemagglutinin markedly decreased the activity of lysates, whether assayed in the presence or absence of catecholamine or fluoride. In contrast, phytohemagglutinin added directly to the assay had no effect. No alternations occurred in adenylate cyclase activity as a result of the incubation of a 1:1 mixture of thymocytes from two strains of mice selected for the capacity of the cells to produce a mixed lymphocyte response.
110 citations