Adenosine Triphosphate-adenosine Research Articles

Actions of p-synephrine on hepatic enzyme activities linked to carbohydrate metabolism and ATP levels in vivo and in the perfused rat liver.

p-Synephrine is one of the main active components of the fruit of Citrus aurantium (bitter orange). Extracts of the bitter orange and other preparations containing p-synephrine have been used worldwide to promote weight loss and for sports performance. The purpose of the study was to measure the action of p-synephrine on hepatic enzyme activities linked to carbohydrate and energy metabolism and the levels of adenine mononucleotides. Enzymes and adenine mononucleotides were measured in the isolated perfused rat liver and in vivo after oral administration of the drug (50 and 300mg/kg) by using standard techniques. p-Synephrine increased the activity of glycogen phosphorylase in vivo and in the perfused liver. It decreased, however, the activities of pyruvate kinase and pyruvate dehydrogenase also in vivo and in the perfused liver. p-Synephrine increased the hepatic pools of adenosine diphosphate and adenosine triphosphate. Stimulation of glycogen phosphorylase is consistent with the reported increased glycogenolysis in the perfused liver and increased glycemia in rats. The decrease in the pyruvate dehydrogenase activity indicates that p-synephrine is potentially capable of inhibiting the transformation of carbohydrates into lipids. The capability of increasing the adenosine triphosphate-adenosine diphosphate pool indicates a beneficial effect of p-synephrine on the cellular energetics.

Difference Between Dormant Conduction Sites Revealed by Adenosine Triphosphate Provocation and Unipolar Pace-Capture Sites Along the Ablation Line After Pulmonary Vein Isolation

Dormant pulmonary vein (PV) conduction revealed by adenosine/adenosine triphosphate (ATP) provocation test and exit block to the left atrium by pacing from the PV side of the ablation line ("pace and ablate" method) are used to ensure durable pulmonary vein isolation (PVI). However, the mechanistic relation between ATP-provoked PV reconnection and the unexcitable gap along the ablation line is unclear.Forty-five patients with atrial fibrillation (AF) (paroxysmal: 31 patients, persistent: 14 patients; age: 61.1 ± 9.7 years) underwent extensive encircling PVI (EEPVI, 179 PVs). After completion of EEPVI, an ATP provocation test (30 mg, bolus injection) and unipolar pacing (output, 10 mA; pulse width, 2 ms) were performed along the previous EEPVI ablation line to identify excitable gaps. Dormant conduction was revealed in 29 (34 sites) of 179 PVs (16.2%) after EEP-VI (22/45 patients). Pace capture was revealed in 59 (89 sites) of 179 PVs (33.0%) after EEPVI (39/45 patients), and overlapping sites, ie, sites showing both dormant conduction and pace capture, were observed in 22 of 179 (12.3%) PVs (17/45 patients).Some of the ATP-provoked dormant PV reconnection sites were identical to the sites with excitable gaps revealed by pace capture, but most of the PV sites were differently distributed, suggesting that the main underling mechanism differs between these two forms of reconnection. These findings also suggest that performance of the ATP provocation test followed by the "pace and ablate" method can reduce the occurrence of chronic PV reconnections.

Adenosine-Provoked Atrial Fibrillation Originating From Non–Pulmonary Vein Foci: The Clinical Significance and Outcome After Catheter Ablation

ObjectivesThe goal of this study was to systematically investigate the incidence and clinical significance of non–pulmonary vein (PV) foci revealed by adenosine/adenosine triphosphate (ATP) testing during atrial fibrillation (AF) ablation. BackgroundATP is reported to provoke AF. MethodsA total of 464 patients with consecutive paroxysmal AF undergoing ATP testing after PV antrum isolation were included. ResultsAF originating from non-PV foci was provoked in 26 (5.6%) total patients during first (n = 20) or repeat (n = 8) ablation procedures. Dormant PV conduction was also revealed by ATP testing in 6 patients. Non-PV foci were located in the superior vena cava (SVC) (i.e., the SVC group) and atria (i.e., the atria group) in 10 and 18 (9 each in the right and left atria) patients, respectively. In the multivariable analysis, being female was the sole independent predictor of ATP-provoked AF originating from non-PV foci (hazard ratio [HR]: 2.52 [95% confidence interval (CI): 1.069 to 5.929]; p = 0.034). After additional ablation targeting non-PV foci, freedom from recurrent AF after the last procedure was similar between the SVC group and patients without ATP-provoked AF but was significantly lower in the atria group than in others (p = 0.0008). Atria group membership (HR: 3.725 [95% CI: 1.692 to 8.199]; p = 0.001) and being female (HR: 1.538 [95% CI: 1.189 to 1.989]; p = 0.001) were significant independent predictors associated with recurrence after the last procedure in the multivariable Cox regression model. ConclusionsATP provoked AF originating from non-PV foci under isoproterenol in 5.6% of patients undergoing paroxysmal AF ablation. ATP testing might be useful for identifying and eliminating AF originating from the SVC. The atria group was associated with a poor outcome after the last procedure despite efforts to eliminate non-PV foci.

Additional effects of monovalent cations on the lysine-sensitive aspartokinase of E. coli B

The apparent specificity of activation of lysine-sensitive aspartokinase (E.C.2.7.2.4) from E. coli by monovalent cations differs depending on the assay used and on the Mg 2+ concentration. Activity is nearly absolutely dependent on and is highly specific for a monovalent cation in the aspartate semialdehyde dehydrogenase coupled assay or the adenosine triphosphate-adenosine diphosphate exchange assay. Little specificity for monovalent cations is observed using the aspartyl hydroxamate assay. Activation and specificity are also altered by Mg 2+ concentrations at a constant 5 mM nucleotide concentration. At a low ( 1.25 or 1.6 mM) Mg 2+ concentration, monovalent cation activation and specificity are nearly absolute. Less dependence on monovalent cations and less specificity are observed at a higher Mg 2+ concentration (6 mM). Li + inhibits aspartokinase competitively with respect to either K + or NH 4 +. Monovalent cations are also thermoprotective and differential thermal inactivation experiments at 56°C reveal that NH 4 + and K +, either of which will produce maximum catalytic activity, interact differently with aspartokinase. K + interacts with positive cooperativity, whereas NH 4 + does not. K +, NH 4 +, and Na + are about equally effective in enhancing the dissociation of the aspartokinase-aspartylphosphate complex. Li + is less effective.

Relaxation of guinea-pig fundic strip by adenosine, adenosine triphosphate and electrical stimulation: lack of antagonism by theophylline or ATP treatment.

1 Theophylline relaxed isolated strips of guinea-pig stomach fundus in a dose-dependent manner; above 50 to 100 microM responses showed no fade for up to 90 min. 2 Relaxant responses to adenosine, adenosine triphosphate (ATP), noradrenaline, and to electric field stimulation of non-adrenergic inhibitory nerves were not affected in a significant manner in the presence of 50 microM theophylline. 3 In tissues which showed complete fade of initial responses in the continued presence of 50 microM ATP, the effects of stimulation of non-adrenergic inhibitory nerves remained unaltered, suggesting that the ATP receptor has no function in non-adrenergic inhibitory transmission in this tissue. 4 These findings are opposite to those of Okwuasaba, Hamilton & Cook (1977), who claimed that 50 microM theophylline almost fully inhibited relaxation induced by adenosine ATP and nerve stimulation and that ATP-induced fade also abolished sensitivity to inhibitory nerve stimulation.

The molecular lesion of hereditary spherocytosis (HS): a continuing enigma [Editorial

V ERY FEW, if any, abnormalities of the human erythrocyte have been studied with such diligence as those associated with hereditary spherocytosis (HS). Not only has the small, round, densely staining spherocyte provided a long-recognized morphologic benchmark, but its inordinate susceptibility to lysis in hypotonic saline has been clearly documented for 75 years.’ Forty years ago, Haden (cited above) and Castle and Daland2 related the latter to loss of the usual discoidal form of the erythrocyte, and to a probable structural abnormality resulting in a decreased surface area/volume ratio. The unique role ofthe spleen in recognizing, sequestering, and finally destroying the abnormal cell, and the effect of splenectomy in correcting clinical manifestations were investigated in great detail in the 1940’s and early l95O’s.�� The assumption that a genetically determined, usually dominantly transmitted7”#{176} abnormality of the red cell membrane lies at the heart of the disorder has pervaded studies of its pathophysiobogyand, in the past 20 years, has fostered many investigations of red cell membrane structure and function. While these studies have added much to our understanding of red cell physiology, the secret of the ultimate molecular lesion still remains locked within the osmotically fragile spherocyte. These investigations have defined a variety of abnormal properties in HS red cells. These cells are abnormally permeable to sodium and this “sodium leak”2 necessitates an increased glycolytic rate to support greater-thannormal adenosine triphosphate-adenosine triphosphatase (ATP-ATPase)dependent pumping of sodium from the cell’s interior.’2’4 While total lipids have been reported to be relatively somewhat decreased both before’5”6 and after’7 splenectomy, and abnormalities of phospholipid turnover have been suggested,’t no consistently demonstrable data thus far support specific abnormalities in membrane lipid structure. However, under conditions of glucose deprivation, HS membrane lipid is abnormally unstable, and is released by a budding process, thus contributing to a still greater deficit in surface area.’5”9’2#{176}

Effects of arginine and some analogues of the partial adenosine triphosphate-adenosine diphosphate exchange reaction catalysed by arginine kinase. Evolutionary divergence in the mechanism of action of a monomer and a dimer arginine kinase

1. Both the monomer arginine kinase from lobster muscle and the dimer arginine kinase from Holothuria forskali catalyse the ATP-ADP partial exchange reaction at rates equal to 3 and 0.6% of the normal rate of transphosphorylation respectively. The Mg2+-nucleotide complex is the substrate for this as it is for the kinase reaction. 2. Analogues of arginine inhibit the exchange reaction of the lobster enzyme but enhance that of the Holothuria enzyme. 3. With the lobster enzyme NO3- has no effect on the exchange reaction alone and inhibit only slightly the apparent enhancement of the exchange reaction produced by the addition of arginine. This is compatible with previous findings for this enzyme that formation of the anion-stabilized dead-end complex, enzyme-arginine-MgADP-NO3-, does not occur to any marked degree. 4. About 80% of the ADP-ATP exchange reaction of the lobster enzyme remains after inhibition with iodoacetamide. This is further decreased to 65% by the addition of L-arginine, indicating that this substrate does bind to the thiolmodified enzyme. 5. It is concluded that the partial exchange reaction is a genuine phenomenon not mediated by trace amounts of arginine. From the effects of arginine and related compounds it would appear that during the normal kinase reaction the partial ATP-ADP exchange reaction is suppressed in the lobster enzyme but enhanced in the Holothuria enzyme. This reflects a remarkable evolutionary divergence of two homologous enzymes.

Effects of laser photocoagulation on adenine nucleotides in rabbit retinas.

High-pressure liquid chromatography was used to provide a qualitative biochemical assessment of laser effects on retinal metabolism. The adenosine triphosphate-adenosine diphosphate ratio and the Atkinson energy charge are considerably increased in laser-treated rabbit retinas compared to the contralateral untreated retinas.

Antimycin A Stimulation of Rate-limiting Steps of Photosynthesis in Isolated Spinach Chloroplasts

Changes in levels of metabolites in isolated spinach (Spinacia oleracea) chloroplasts seen upon addition of antimycin A suggest that the activities of enzymes mediating several regulated reactions are affected. Apparently, the presence of added antimycin A does not increase the level of CO(2) in the chloroplasts, nor does it stimulate CO(2) fixation by increasing the level of the carboxylation substrate, ribulose-1,5-diphosphate. Rather, it appears that antimycin A increases CO(2) fixation rate by indirectly stimulating the enzyme, ribulose-1,5-diphosphate carboxylase (E.C. 4.1.1.39), which mediates the carboxylation of ribulose-1,5-diphosphate to give 3-phosphoglycerate. Another rate-limiting enzyme of the reductive pentose phosphate cycle, hexose diphosphatase (E.C. 3.1.3.11), seems also to be stimulated. The synthesis of polysaccharides (mostly starch) seems also to be stimulated. These results are interpreted as indicating that antimycin A addition enhances the general activation of those enzymes which already are activated during photosynthesis but are inactive in the dark. The ratio of adenosine triphosphate-adenosine diphosphate under conditions of photosynthesis was only moderately decreased in the presence of antimycin A, perhaps accounting in part for an observed increase in accumulation of 3-phosphoglycerate as compared with dihydroxyacetone phosphate. No significant effect on movement of metabolites from the chloroplast to the medium was seen.

Properties of a Nucleoside Diphosphokinase from Liver Mitochondria and Its Relationship to the Adenosine Triphosphate-Adenosine Diphosphate Exchange Reaction

A nucleoside diphosphokinase which also catalyzes an adenosine triphosphate-adenosine diphosphate exchange reaction has been extracted from bovine liver mitochondria and purified by conventional methods of protein fractionation. A comparison of the catalytic properties of the two activities indicates that both are catalyzed by the same enzyme, which is different in several respects from the nucleoside diphosphokinase previously isolated by others from rat liver and from erythrocytes. Evidence is presented that the enzyme herein described also catalyzes the dinitrophenol-sensitive ATP-ADP exchange reaction when bound to intact mitochondria and to phosphorylating submitochondrial particles.

Inactivation of Rabbit Muscle Adenosine Triphosphate-Adenosine 5'-Phosphate Phosphotransferase by Alkylation of Methionine Residues

Abstract The reaction of rabbit muscle myokinase with dithiobis(2-nitrobenzoic acid) results in the formation of a stable, soluble, and enzymatically inactive derivative in which both reactive sulfhydryl groups on the enzyme have been reversibly protected. Myokinase activity is completely regenerated by the addition of dithiothreitol to the derivative. Alkylation of the myokinase derivative with iodoacetic acid at pH 2.4 completely prevents regeneration of activity by dithiothreitol. Amino acid analysis shows that the loss in activity is due to the specific modification of 2 to 3 methionine residues. A magnetic resonance study (proton relaxation rate) showed that alteration of the methionine had greatly reduced the capacity of the enzyme to form an enhanced ternary complex with nucleotide substrates.

Distribution of an Oligomycin-sensitive Adenosine Triphosphate-Adenosine Diphosphate Exchange Reaction and Its Relationship to the Respiratory Chain

Distribution of an Oligomycin-sensitive Adenosine Triphosphate-Adenosine Diphosphate Exchange Reaction and Its Relationship to the Respiratory Chain

Nucleotide Transphosphorylases from Liver: I. PURIFICATION AND PROPERTIES OF AN ADENOSINE TRIPHOSPHATE-ADENOSINE MONOPHOSPHATE TRANSPHOSPHORYLASE FROM SWINE LIVER

Nucleotide Transphosphorylases from Liver: I. PURIFICATION AND PROPERTIES OF AN ADENOSINE TRIPHOSPHATE-ADENOSINE MONOPHOSPHATE TRANSPHOSPHORYLASE FROM SWINE LIVER

Action of chlorpromazine. 3. Mitochondrial adenosine triphosphatase and the adenosine triphosphate-adenosine diphosphate exchange.

Action of chlorpromazine. 3. Mitochondrial adenosine triphosphatase and the adenosine triphosphate-adenosine diphosphate exchange.

The Adenosine Triphosphate-Adenosine Diphosphate Exchange Reaction of Oxidative Phosphorylation

The Adenosine Triphosphate-Adenosine Diphosphate Exchange Reaction of Oxidative Phosphorylation