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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Dose of theophylline and caffeine which do not produce aortic arch anomalies in embryonic chicks have been shown to potentiate catecholamine-induced aortic arch malformations in that experimental animal. Theophylline (2.1 X 10(-5) mole per milliliter isotonic saline solution) potentiated the effective dose of norepinephrine more than 100 times. The greatest potentiation observed with epinephrine (2.5 X) was induced by 2.6 X 10(-5) mole caffeine. This study also demonstrated that both methylxanthines specifically induce aneurysms of the ascending aorta and complete absence (or nearly complete constriction) of the right ductus arteriosus. The incidences of these types of cardiovascular malformations proved to be dose dependent with theophylline a more potent teratogen than caffeine. The mobilization of calcium and/or cyclic nucleotide phosphodiesterase inhibition by the methylxanthines are suggested as significant actions in the potentiation of catecholamine-induced aortic arch anomalies.
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PMID:The effects of methylxanthines on catecholamine-stimulated and normal chick embryos. 19 58

1. The hydrolysis of guanosine triphosphate (GTP) and the consequent formation of guanosine diphosphate (GDP) and phosphate (P1) are activated by light in a suspension of broken retinal rods: the hydrolysis rate with GTP in the micrometer concentration range is 2.5-3.5 n-mole/min per mg of rhodopsin in the preparation. 2. The ionic composition of the medium suspending the rods is not critical: the hydrolysis is present in NaCl saline solution with MG2+ as well as in Tris-HC1 buffer solution, and with the chelating agent EDTA. 3. The ionic strength is critical: the effect is reduced when the broken rods are suspended in a low salt mannitol solution, and is altogether abolished when they are separated from the mannitol solution; it reappears when the mannitol solution is added again in the presence of salts. An element essential for the effect is thus reversibly released in the mannitol solution. No hydrolytic activity on GTP, however, is found in the mannitol soluble fraction. 4. The cyclic nucleotide phosphodiesterase is eluted from the rods in the mannitol solution, and is reaggregated to the rods in the presence of salts; once recombined with the rods, it can be activated by light. 5. The activation of the phosphodiesterase by light is present in the absence of added nucleotide triphosphates.
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PMID:Light-activated hydrolysis of GTP and cyclic GMP in the rod outer segments. 20 80

Acetylation at the alpha-amino terminal is a common post-translational modification of many peptides and proteins. In the case of the potent opiate peptide beta-endorphin, alpha-N-acetylation is a known physiological modification that abolishes opiate activity. Since there are no known receptors for alpha-N-acetyl-beta-endorphin, we have studied the association of this peptide with calmodulin, a calcium-dependent protein that binds a variety of peptides, phenothiazines, and enzymes, as a model system for studying acetylated endorphin-protein interactions. Association of the acetylated peptide with calmodulin was demonstrated by cross-linking with bis(sulfosuccinimidyl)suberate; like beta-endorphin, adducts containing 1 mol and 2 mol of acetylated peptide per mole calmodulin were formed. Some of the bound peptides are evidently in relatively close proximity to each other since, in the presence of amidated (i.e., lysine-blocked) calmodulin, cross-linking yielded peptide dimers. The acetylated peptide exhibited no appreciable helicity in aqueous solution, but in trifluoroethanol (TFE) considerable helicity was formed. Also, a mixture of acetylated peptide and calmodulin was characterized by a circular dichroic spectrum indicative of induced helicity. Empirical prediction rules, applied earlier to beta-endorphin, suggest that residues 14-24 exhibit alpha-helix potential. This segment has the potential of forming an amphipathic helix; this structural unit is believed to be important in calmodulin binding. The acetylated peptide was capable of inhibiting the calmodulin-mediated stimulation of cyclic nucleotide phosphodiesterase (EC 3.1.4.17) activity with an effective dose for 50% inhibition of about 3 microM; this inhibitory effect was demonstrated using both an enzyme-enriched preparation as well as highly purified enzyme. Thus, acetylation at the alpha-amino terminal of beta-endorphin, although abolishing opiate activity, does not interfere with the binding to calmodulin. Indeed, beta-endorphin and the alpha-N-acetylated peptide behave very similarly with respect to calmodulin association.
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PMID:Interaction of alpha-N-Acetyl-beta-endorphin and calmodulin. 285 97

The relation of cyclic 3',5'-adenosine monophosphate to platelet function has been studied by investigating the influence of this compound and of its N(6)-2'-0-dibutyryl derivative on platelet aggregation and other aspects of platelet behavior after demonstration of adenyl cyclase activity in disrupted platelets. Dibutyryl cyclic AMP inhibited platelet aggregation induced by ADP, epinephrine, collagen, and thrombin. Cyclic AMP was also inhibitory but was less effective. The platelet "release reaction" was also inhibited; specifically, there was inhibition of the induction of platelet factor 3 activity and of the release of labeled 5-hydroxytryptamine. Platelet swelling produced by ADP was not inhibited. The action of dibutyryl cyclic AMP did not result from contamination with 5'-AMP, nor was it attributable to production of 5'-AMP by plasma enzymes. Dibutyryl cyclic AMP was degraded to 2'-O-monobutyryl cyclic AMP and to cyclic AMP in plasma, but plasma exhibited no cyclic nucleotide phosphodiesterase activity, and the production of 5'-AMP did not occur. The in vitro effects of dibutyryl cyclic AMP were associated with uptake of the compound by platelets. Adenyl cyclase activity of platelet homogenates was demonstrated with production of 9.27 x 10(-11) (+/-2.62 x 10(-11)) mole cyclic AMP per min per 10(10) platelets. The activity was increased by NaF and by prostaglandin PGE(1) and was decreased by epinephrine. The effect of epinephrine was blocked by phentolamine but not by propanolol. Adenyl cyclase activity was also inhibited by collagen, 5-hydroxytryptamine, and thrombin. ADP, dibutyryl cyclic AMP, and cyclic AMP did not alter adenyl cyclase activity. These observations are consistent with the hypothesis that platelet aggregation is favored by a decrease in platelet cyclic AMP and inhibited by an increase in cyclic AMP.
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PMID:Cyclic 3',5'-adenosine monophosphate in human blood platelets. II. Effect of N6-2'-o-dibutyryl cyclic 3',5'-adenosine monophosphate on platelet function. 432 65

The substrate specificity of diadenosine 5',5"'-P1,P4-tetraphosphate pyrophosphohydrolase from Physarum polycephalum for dinucleoside polyphosphates has been determined by high-performance liquid chromatography (HP-LC). Elution of a strong anion-exchange resin with a pH and ionic strength gradient of ammonium phosphate separates a series of monoadenosine and diadenosine polyphosphates. Most of the corresponding guanine nucleotides are also resolved on this HPLC system. One mole each of Ap4A and Gp4G is symmetrically hydrolyzed to 2 mol of ADP and GDP, respectively. Ap3A, Ap5A, Ap6A, and Ap4 are hydrolyzed, and in each case ADP is one of the products. Gp3G, Gp5G, Gp6G, and Gp4 are also substrates, and in each case GDP is one of the products. AMP, ADP, ATP, Ap2A, ADPR, GMP, GDP, GTP, NAD+, and NADP+ are not substrates. No hydrolysis of the cap dinucleotides m7Gp3Am and m7Gp3Cm was detected by HPLC. Diadenosine tetraphosphate pyrophosphohydrolase preparations were also assayed for adenylate kinase, nucleotide diphosphate kinase, NAD(P)+ pyrophosphohydrolase, phosphodiesterase, cyclic nucleotide phosphodiesterase, phosphatase, and ribonuclease activities. These enzymic activities were not detectable in diadenosine tetraphosphate pyrophosphohydrolase. The symmetrical hydrolysis of Ap4A and Gp4G is an unique catalytic property that distinguishes diadenosine tetraphosphate pyrophosphohydrolase from P. polycephalum from diadenosine tetraphosphate phosphohydrolases from other organisms.
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PMID:Diadenosine 5',5"'-P1,P4-tetraphosphate pyrophosphohydrolase from Physarum polycephalum. Substrate specificity. 629 57