Suramin--a powerful inhibitor of neural ecto-diadenosine polyphosphate hydrolase

The neural ecto-diadenosine polyphosphate hydrolase (ecto-ApnAase) from plasma membranes of Torpedo synaptic terminals is inhibited by suramin. This study was carried out by discontinuous h.p.l.c. and continuous fluorometric methods. The concentration-dependence studies showed a non-competitive mechanism for suramin in the Dixon plot, with a Ki value of 1.79 +/- 0.03 microM with respect to epsilon-(Ap3A) as the substrate and 1.69 +/- 0.05 microM and 1.86 +/- 0.06 microM for epsilon-(Ap4A) and epsilon-(Ap5A) respectively. These results indicate that suramin could be a base compound inhibiting ecto-ApnAase and providing an alternative way of studying the pharmacology of diadenosine polyphosphate receptors.