SURAMIN - A POWERFUL INHIBITOR OF NEURAL ECTO-DIADENOSINE POLYPHOSPHATE HYDROLASE

The neural ecto-diadenosine polyphosphate hydrolase (ecto-Ap(n)Aase) f rom plasma membranes of Torpedo synaptic terminals is inhibited by sur amin. This study was carried out by discontinuous h.p.l.c. and continu ous fluorometric methods. The concentration-dependence studies showed a non-competitive mechanism for suramin in the Dixon plot, with a K-i value of 1.79+/-0.03 mu M with respect to epsilon-(Ap(3)A) as the subs trate and 1.69+/-0.05 mu M and 1.86+/-0.06 mu M for epsilon-(Ap(4)A) a nd epsilon-(Ap(5)A) respectively. These results indicate that suramin could be a base compound inhibiting ecto-Ap(n)Aase and providing an al ternative way of studying the pharmacology of diadenosine polyphosphat e receptors.