Hydrolyzes diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) to yield ADP. H2O + P(1),P(4)-bis(5'-adenosyl) tetraphosphate = 2 ADP + 2 H(+) Homodimer. Mutant shows increased levels of Ap4G, Ap4U, Ap3A and Ap4A (PubMed:32152217). Cells form pellicles that are initially flat and thin. The pellicles finally become thicker, their flat surfaces are broken by a number of broad pits, the inner surface of which are covered with fruiting bodies. The colonies also show a defect in gross morphology, in that their central region is flat ang glossy (PubMed:15175311). Belongs to the Ap4A hydrolase YqeK family.