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PubMed1975

Synthesis of adenosine triphosphate and exchange between inorganic phosphate and adenosine triphosphate in sodium and potassium ion transport adenosine triphosphatase.

Radioactive adenosine triphosphate was synthesized transiently from adenosine diphosphate and radioactive inorganic phosphate by sodium and potassium adenosine triphosphatase from guinea pig kidney. In a first step, K+-sensitive phosphoenzyme was formed from radioactive inorganic phosphate in the presence of magnesium ion and 16 mM sodium ion. In a second step the addition to the phosphoenzyme of adenosine diphosphate with a higher concentration of sodium ion produced adenosine triphosphate. Recovery of adenosine triphosphate from the phosphoenzyme was 10 to 100% in the presence of 96 to 1200 mM sodium ion, respectively. Potassium ion (16mM) inhibited synthesis if added before or simultaneously with the high concentration of sodium ion but had no effect afterward. The half-maximal concentration for adenosine diphosphate was about 12 muM. Ouabain inhibited synthesis. The ionophore gramicidin had no significant effect on the level of phosphoenzyme nor on the rate nor on the extent of synthesis of adenosine triphosphate. The detergent Lubrol WX reduced the rate of phosphoenzyme break-down and the rate of synthesis but did not affect the final recovery. Phospholipase A treatment inhibited synthesis. In a steady state, the enzyme catalzyed a slow ouabain-sensitive incorporation or inorganic phosphate into adenosine triphosphate. These results and other suggest that binding of sodium ion to a low affinity site on phosphoenzyme formed from inorganic phosphate is sufficient to induce a conformational change in the active center which permits transfer of the phosphate group to adenosine diphosphate.

Adenosine Triphosphatases↗
PubMed1997

Release of adenosine triphosphate by adenosine diphosphate in whole blood and in erythrocyte suspensions.

In whole blood samples from thrombocytopenic patients, large amounts of ATP were released by ADP, exceeding the level obtained with samples from normal persons by far. Because we suspected that the high potential of ATP in erythrocytes would be the main source for this phenomenon, the release of ATP by ADP was measured in whole blood samples from normal, thrombocytopenic, and leukocytopenic persons and in suspensions of washed erythrocytes. The release was recorded by a Whole Blood Lumi-Aggregometer type 500 VS (Chrono-Log Corporation, Havertown, PA) using the luciferin-luciferase system. Not only in samples from thrombocytopenic persons but also with normal platelet count, increasing amounts of ATP were released with increasing ADP concentrations, finally exceeding the ATP releasable from thrombocytes by thrombin. The amounts of ADP required to match the ATP release of thrombin were closely correlated with the platelet counts in the samples. With lower platelet counts, the release mechanism from erythrocytes could be stimulated more easily by low concentrations of ADP. The binding of ADP to platelets occurred with ostensibly higher affinity. The phenomenon of overshooting ATP release was also observed in samples from extremely leukocytopenic patients. A very large release of ATP was also achieved in suspensions of washed erythrocytes. In this way our hypothesis of ATP release from erythrocytes by ADP was confirmed again. The mechanism of the release from erythrocytes remains unclear. We speculate that its purpose is to regulate extracellular nucleotides in the circulating blood.

Adenosine Diphosphate↗
PubMed1985

Profile of prostaglandins generated in the detrusor muscle of rat urinary bladder: effects of adenosine triphosphate and adenosine.

The generation and release of PGE2, PGF2 alpha, PGD2, TXB2 and 6-keto-PGF1 alpha in the rat detrusor muscle were studied by means of radioimmunoassays. The effect of ATP (0.1 mmol/1) and adenosine (0.1 mmol/1) on the content and profile of PGs in the incubation medium was investigated. It was found that PGE2 and 6-keto-PGF1 alpha accounted for more than 80% of the total PG activity. ATP increased the amounts of PGs in the incubation medium (percentage change of the control values, N = 6: PGE2 54.53 +/- 12.69, PGF2 alpha 31.01 +/- 8.82, PGD2 44.52 +/- 12.36, TXB2 17.29 +/- 10.45, 6-keto-PGF1 alpha 36.62 +/- 5.0) but did not change their profile. Adenosine had no effect on either content or profile of the PGs. The results suggest that ATP but ot adenosine may activate PG biosynthesis via P2-purinoceptor-mediated mechanisms.

Adenosine↗
PubMed1989

Adenosine 5'-triphosphate, adenosine and endothelium-derived relaxing factor in hypoxic vasodilatation of the heart.

The involvement of ATP in hypoxic vasodilatation was investigated using isolated perfused guinea-pig hearts (Langendorff). Reactive blue 2, a selective P2Y-purinoceptor antagonist, attenuated dilatations due to ATP and hypoxia. Hydroquinone, an agent which destroys endothelium-derived relaxing factor, substantially decreased dilatations due to 2-methylthioATP, a potent P2Y-purinoceptor agonist, and hypoxia, but not to adenosine. ATP may, therefore, have an important role to play in the initiation of hypoxic dilatation which is mediated by the release of endothelium-derived relaxing factor.

Adenosine↗
PubMed1987

Significance of release of adenosine triphosphate and adenosine induced by hypoxia or adrenaline in perfused rat heart.

The status of ATP as a possible coronary vasodilator remains poorly understood. The onset of hypoxia induced a rapid and transient increase of the ATP concentration in the coronary effluent of the isolated perfused rat heart from 0.8 +/- 0.2 nM to the average peak value of 1.3 +/- 0.2 nM (P less than 0.01) at 2 +/- 0.5 min; at the same time the coronary flow increased 2-fold so that the rate of ATP release increased from 10.2 +/- 2.9 to 21.4 +/- 4.2 pmol/g/min (P less than 0.005). Hypoxia also produced a peak rate release of adenosine of 93 +/- 5 nM/g/min occurring only after the peak increase of coronary flow and also after the peak release of ATP; at peak coronary flow, however, the adenosine concentration was sufficient for vasodilation (0.31 +/- 0.19 microM). Peak release of ATP and of adenosine preceded that of lactate dehydrogenase. 10(-6) M adrenaline induced a rapid increase of coronary flow and release of ATP, the concentration of which rose from 0.9 +/- 0.3 nM to an average peak of 1.7 +/- 0.2 nM (P less than 0.01) at 2 +/- 0.3 min. The rate of increase of ATP in the coronary effluent paralleled the rate of early rise of coronary flow, yet adenosine had also risen to vasodilatory values (0.28 +/- 0.5 microM). The absolute changes in the measured concentrations of ATP in the coronary effluent were more variable and 1000 X less in concentration than those of adenosine. Hence coronary dilation could be explained by adenosine without involving ATP, although an additional vasodilatory role for ATP could not be excluded, especially in the early phases of vasodilation. In one condition, hypoxic K-arrested hearts, the increase in coronary flow could not be linked to release of either adenosine or ATP. The changes in concentrations of potential vasodilators measured in the coronary effluent do not necessarily reflect changes in the interstitial fluid.

Adenosine↗
PubMed1975

The control of tricarboxylate-cycle oxidations in blowfly flight muscle. The oxidized and reduced nicotinamide-adenine dinucleotide content of flight muscle and isolated mitochondria, the adenosine triphosphate and adenosine diphosphate content of mitochondria, and the energy status of the mitochondria during controlled respiration.

1. A study is presented of the mitochondrial NADH content during controlled (state 4) and active (state 3) pyruvate oxidation by blowfly flight-muscle mitochondria. The results confirm and extend those of an earlier study (Hansford, 1972), which indicated an increased reduction in state 3. Nicotinamide nucleotide is normally highly oxidized during state 4; however, there can be substantial reduction in the presence of carnitine or high concentrations of proline, or on lengthy incubation in the presence of either of the systems used to generate intramitochondrial tricarboxylate-cycle intermediate. 2. Omission of phosphate leads to substantial reduction and this can be reversed by adding phosphate or acetate. 3. Estimations of NAD-+ and NADH in fly thoraces show a marked increase in NADH on flight, tending to corroborate the results of mitochondrial experiments and testifying to the importance of dehydrogenase activation in this tissue. 4. Determination of intramitochondrial adenine nucleotides reveals a total of 4-5 nmol/mg of protein, and an ADP content of less than 0.1 nmol/mg during state 4 oxidation of pyruvate and proline. ATP content is found to increase slowly during state 4 and this is attributed to the net phosphorylation of AMP. 5. The uncoupling agent carbonyl cyanide p=trifluoromethoxyphenylhydrazone leads to hydrolysis of some, but not all, of the mitochondrial ATP. Studies of mitochondrial ATPase (adenosine triphosphatase), measured by external pH change, show that it is inactive unless the mitochondria are allowed to respire for several minutes in state 4 in the presence of phosphate before the addition of carbonyl cyanide p-trifluoromethoxyphenylhydrazone. It is suggested that phosphate uptake is essential for maximal ATPase activity. 6. Studies of the fluorescence of the fluorochrome 8-anilino-1-naphthalensulphonic acid suggest that the energy status of the mitochondrion is high during state 4-pyruvate oxidattion, and decrease slightly in state 3. The implications of these findings are discussed.

Adenosine Diphosphate↗
PubMed1976

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.

Adenosine Diphosphate↗