P1,P5-Di(adenosine-5′) pentaphosphate (Ap5A) is a diadenosine polyphosphate, which has a tail-to-tail dimer structure. Ap5A is synthesized in a twostep process involving the formation of adenosine 5′-tetraphosphate (P4A) from the ATP and trimeta-phosphate (P3). In the second step, P4A is converted to Ap5A. The synthesis of Ap5A requires a pH optimum in the range of 7.5 to 8.5 and is modulated by metal ions.
A diadenosine polyphosphate stored in secretory granules of thrombocytes, chromaffin and neuronal cells. After release into the extracellular space, it affects a variety of biological activities in a wide range of target tissues. In the nervous system it acts through various purinergic receptors. It also activates 5′-nucleotidase and inhibits adenosine kinase activity in vitro. Ap5A is metabolized by soluble enzymes in the blood plasma and by membrane-bound ectoenzymes of a number of cell types including endothelial and smooth muscle cells. In cardiac muscle, pM to nM concentrations significantly increase the open-probability of ryanodine-receptor (RyR2) gates, with prolonged action due to slow dissociation from the receptor.
![A[5']P5[5']A SODIUM SALT Structure](/CAS/GIF/4097-04-5.gif)