Diadenosine tetraphosphate activates AMP deaminase from rat muscle.

Diadenosine tetraphosphate, Ap4A, doubled the activity of AMP deaminase from rat muscle, with an activation constant of 0.005 mM, in the presence of 0.05 mM AMP. The presence of Ap4A appeared to induce Michaelian kinetic behavior. The activation by Ap4A was not dependent on the presence of either MgCl2 or KCl in the reaction mixture. Diguanosine tetraphosphate was inhibitor of the enzyme. Diadenosine and diguanosine triphosphates, adenylosuccinate and xanthosine monophosphate were neither inhibitors nor activators of the reaction.