  2.7.99.B1 | 2 ATP = diadenosine 5',5''''-P1,P4-tetraphosphate + diphosphate |
overall reaction. LysU possesses a dual catalytic activity, initially producing 5,5-P1,P4-tetraphosphate from ATP, before converting that tetraphosphate to a triphosphate (diadenosine 5,5-P1,P3-triphosphate (Ap3A) synthase activity). It is shown that 5,5-P1,P3-triphosphate formation requires (1) that the second step of 5,5-P1,P4-tetraphosphate formation is slightly reversible, leading to a reappearance of adenylate intermediate, and (2) that phosphate is present to trap the intermediate. 5,5-P1,P3-triphosphate forms readily from 5,5-P1,P4-tetraphosphate in the presence of phosphate-based adenylate traps via a reverse-trap mechanism (5,5-P1,P4-tetraphosphate + diphosphate= 5,5-P1,P3-triphosphate + phosphate) |
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