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PubMed1976

A simple, rapid, efficient method for the preparation of gamma 32P-labeled guanosine triphosphate (GTP) and adenosine triphosphate (ATP).

A simplified new method for synthesis fo gamma 32P GTP and gamma 32P ATP is described. Radiophosphorus is incorporated into GDP and ADP to form GTP and ATP, respectively, in the phosphoglycerate kinase reaction. The product is separated by ion exchange resin chromatography. The procedure is simple, gives a product a high purity, and the label is confined to the gamma position.

Adenosine Triphosphate↗
PubMed1995

Inhibition of insulin receptor phosphorylation by PC-1 is not mediated by the hydrolysis of adenosine triphosphate or the generation of adenosine.

Individuals with insulin resistance show increased levels of PC-1 expression in skeletal muscle and fibroblasts, and in transfected cell lines that overexpress PC-1 there is a reduction in the insulin-stimulated insulin receptor tyrosine phosphorylation. As PC-1 is a type II transmembrane protein with extracellular phosphodiesterase and pyrophosphatase activity, increased expression of PC-1 at the cell surface will decrease extracellular adenosine triphosphate levels and increase extracellular adenosine levels. Consequently it is possible that PC-1-mediated insulin resistance could be caused either by a decrease in adenosine triphosphate or an indirect increase in adenosine levels. We have tested this hypothesis and find that the PC-1-mediated inhibition of insulin-stimulated insulin receptor autophosphorylation is not altered by agents that alter the level or action of adenosine. Further, a mutated PC-1 with a single amino acid change that abolishes the phosphodiesterase and pyrophosphatase activities is still able to inhibit insulin-stimulated insulin receptor phosphorylation. The results of these experiments indicate that the phosphodiesterase activity of PC-1 is not involved in the inhibition of insulin receptor autophosphorylation.

Adenosine↗
PubMed1974

The magnesium ion-dependent adenosine triphosphatase of myosin. Two-step processes of adenosine triphosphate association and adenosine diphosphate dissociation.

The kinetics of protein-fluorescence change when rabbit skeletal myosin subfragment 1 is mixed with ATP or adenosine 5'-(3-thiotriphosphate) in the presence of Mg(2+) are incompatible with a simple bimolecular association process. A substrate-induced conformation change with DeltaG(0)<-24kJ.mol(-1) (i.e. DeltaG(0) could be more negative) at pH8 and 21 degrees C is proposed as the additional step in the binding of ATP. The postulated binding mechanism is M+ATPright harpoon over left harpoonM.ATPright harpoon over left harpoonM*.ATP, where the association constant for the first step, K(1), is 4.5x10(3)m(-1) at I 0.14m and the rate of isomerization is 400s(-1). In the presence of Mg(2+), ADP binds in a similar fashion to ATP, the rate of the conformation change also being 400s(-1), but with DeltaG(0) for that process being -14kJ.mol(-1). The effect of increasing ionic strength is to decrease K(1), the kinetics of the conformation change being essentially unaltered. Alternative schemes involving a two-step binding process for ATP to subfragment 1 are possible. These are not excluded by the experimental results, although they are perhaps less likely because they imply uncharacteristically slow bimolecular association rate constants.

Adenosine Diphosphate↗
PubMed1994

Time course of the recovery of adenosine triphosphate content with adenosine in post-ischemic hearts--a 31P magnetic resonance spectroscopy study.

Restoration of the ATP level after brief ischemia is limited by slow de novo ATP synthesis and substrate loss in a salvage pathways for ATP synthesis, and complete recovery requires several days in the stunned heart. Adenosine is a substrate for myocardial ATP synthesis. We measured myocardial ATP in both ex vivo and in vivo experiments by 31P magnetic resonance spectroscopy (31P-MRS) and investigated the time course of ATP content recovery after application of adenosine. Guinea-pig perfused hearts were subjected to 30 min of global ischemia and reperfused for 3 h with 50 microM adenosine. The ATP level increased from 54 +/- 5% to 117 +/- 4% of the pre-ischemic value (p < 0.01). In dogs, we occluded the left anterior descending coronary artery for 40 min to produce regional ischemia. Afterwards, we administered 100 mumol/h adenosine into the left ventricle for 2 h. ATP levels increased from 63 +/- 4% to 77 +/- 5% of the pre-ischemic value with adenosine (p < 0.05). However, ATP levels did not increase for a few hours after reperfusion both ex vivo and in vivo. Our 31P-MRS studies demonstrated that brief ischemia depressed ATP levels and that administration of adenosine accelerated ATP formation in post-ischemic hearts.

Adenosine↗
PubMed1976

Synthesis of bound adenosine triphosphate from bound adenosine diphosphate by the purified coupling factor 1 of chloroplasts. Evidence for direct involvement of the coupling factor in this "adenylate kinase-like" reaction.

Electrophoretically homogeneous coupling factor 1 from spinach chloroplasts binds ADP and converts the bound ADP to bound ATP and AMP. That this transphosphorylation of enzyme-bound ADP is catalyzed by the coupling factor itself, and not be a conventional adenylate kinase which might possibly contaminate preparations of the coupling factor, is supported by the following evidence. 1. The procedure for isolatio of the coupling factor is designed to separate this large (approximately 13 S) enzyme from the smaller (4.2 S) conventional adenylate kinase of spinach chloroplasts. The conventional adenylate kinase cannot be detected in purified preparations of the coupling factor by biochemical assay or by polyacrylamide gel electrophoresis. 2. The activity of spinach adenylate kinase is completely dependent upon magnesium ions. However, the production of bound ATP and AMP from bound ADP by the coupling factor can be assayed in the total absence of added magnesium ions or even in the presence of added EDTA. 3. Comparative studies with inhibitors show that the coupling factor can produce bound ATP from ADP under conditions where the activity of adenylate kinase is strongly inhibited. Conversely, the coupling factor is prevented from synthesizing bound ATP from ADP under other conditions where the conventional adenylate kinase has high levels of activity. 4. AMP, when added in solution to the coupling factor, does not bind to this enzyme, even in the presence of APT. Thus, it is unlikely that the appearance of AMP bound to the coupling factor after its incubation with ADP is due to the production of free AMP by contaminating adenylate kinase. These results demonstrate that the isolated, homogeneous coupling factor from spinach chloroplasts has the intrinsic capacity to perform a phosphoryl group transfer between two bound ADP molecules and thus to synthesize ATP. This reaction may have an important role in the photosynthetic production of ATP by the chloroplast, as is discussed in this communication.

Adenosine Diphosphate↗