Ca2+ dependency of diadenosine 5',5"'-p1,p4-tetraphosphate degradation in dog plasma.

Diadenosine 5',5"'-p1,p4-tetraphosphate (Ap4A) degradation in dog plasma was inhibited by the addition of EDTA. The Ap4A degrading activity seemed to be recovered by the addition of metal ions, Ca2+, Co2+, Cu2+, Mg2+, Mn2+ or Zn2+ to plasma in which the activity was lost by the addition of EDTA. Especially, the degradation was accelerated by the addition of Ca2+ to the plasma, and the degradation rate was dependent on the concentration of Ca2+. The results of this study suggested that the enzymatic degradation of Ap4A in dog plasma was modulated by the concentration of Ca2+.