ATP adenylyltransferase

In enzymology, an ATP adenylyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are ADP and ATP, whereas its two products are phosphate and P1,P4-bis(5'-adenosyl) tetraphosphate.
This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing nucleotide groups (nucleotidyltransferases). The systematic name of this enzyme class is ADP:ATP adenylyltransferase. Other names in common use include bis(5'-nucleosyl)-tetraphosphate phosphorylase (NDP-forming), diadenosinetetraphosphate alphabeta-phosphorylase, adenine triphosphate adenylyltransferase, diadenosine 5',5'"-P1,P4-tetraphosphate alphabeta-phosphorylase, (ADP-forming), and dinucleoside oligophosphate alphabeta-phosphorylase. This enzyme participates in purine metabolism.