Presence of diguanosine tri, tetra-, and pentaphosphates in commercial samples of GTP and guanosine 5'-tetraphosphate

Dinucleoside polyphosphates-friend or foe?

Despite being known for over 30 years, the functions of the dinucleoside polyphosphates, such as diadenosine 5',5"'-P(1), P(4)-tetraphosphate (Ap(4)A) and diadenosine 5',5"'-P(1), P(3)-triphosphate (Ap(3)A), are still unclear. On the one hand, they may have important signalling functions, both inside and outside the cell (friend), while on the other hand, they may simply be the unavoidable by-products of certain biochemical reactions, which, if allowed to accumulate, would be potentially toxic through their structural similarity to ATP and other essential mononucleotides (foe). Here, the occurrence, synthesis, degradation, and proposed functions of these compounds are briefly reviewed, along with some new data and recent evidence supporting roles for Ap(3)A and Ap(4)A in the cellular decision making processes leading to proliferation, quiescence, differentiation, and apoptosis. Hypotheses are forwarded for the involvement of Ap(4)A in the intra-S phase DNA damage checkpoint and for Ap(3)A and the pFhit (fragile histidine triad gene product) protein in tumour suppression. It is concluded that the roles of friend and foe are not incompatible, but are distinguished by the concentration range of nucleotide achieved under different circumstances.

Diadenosine 5',5"-P1,P4-tetraphosphate (Ap4A), ATP and catecholamine content in bovine adrenal medulla, chromaffin granules and chromaffin cells

The level of diadenosine 5',5"-P1-P4-tetraphosphate (diadenosine tetraphosphate or Ap4A), catecholamines, ATP and other nucleotides has been investigated in perchloric acid extracts of bovine adrenal medulla, chromaffin granules and cultured chromaffin cells. As a control, the amount of Ap4A and ATP has also been measured in human blood platelets. The following values (nmol/mg protein) were found in adrenal medulla: Ap4A, 0.019 +/- 0.004; ATP, 109 +/- 11; ADP, 23.8 +/- 5.8; AMP, 11.3 +/- 1.5; p4A, 0.18 +/- 0.08; catecholamines, 460 +/- 57. The level of Ap4A, catecholamines and ATP (nmol/mg protein) found in chromaffin granules and in chromaffin cells were, respectively: (0.15 +/- 0.07; 2175 +/- 99; 531 +/- 66) and (0.22 +/- 0.14; 1143 +/- 277; 222 +/- 53). In all the cases investigated, the ratio catecholamines/ATP and catecholamines/Ap4A were around 5 and in the order of 10(3), respectively. The amount of Ap4A found here, in bovine adrenal medulla, chromaffin granules and chromaffin cells, is two orders of magnitude lower than previously reported.