<p>Diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) is a regulatory metabolite of stress conditions. It is hydrolyzed to two ADP by Bis(5'-nucleosyl)-tetraphosphatase (symmetrical) (<db_xref db="EC" dbkey="3.6.1.41"/>). Alternate names include diadenosine-tetraphosphatase and Ap4A hydrolase [<cite idref="PUB00014455"/>].</p>