Members of this family of proteins catabolise Ap4N nucleotides (where N is A,C,G or U). Additionally they catalyse the conversion of adenosine-5-phosphosulfate (AMPs) plus Pi to ADP plus sulphate, the exchange of NDP and phosphate and the synthesis of Ap4A from AMPs plus ATP [1].

1: Sequencing and enhanced expression of the gene encoding diadenosine 5',5'''-P1, P4-tetraphosphate (Ap4A) phosphorylase in Saccharomyces cerevisiae. Kaushal V, Avila DM, Hardies SC, Barnes LD; Gene. 1990;95:79-84. PMID:2174812