Hydrolysis of nucleoside phosphates, III. The dephosphorylation of adenosine 5'-triphosphate in a binary and ternary Zn2+ complex.

The dephosphorylation of ATP was characterized by determining the dependence of the firstorder rate constant on pH in the absence and presence of Zn2+ and together with Zn2+ and 2,2'-bipyridyl. The Zn2+-accelerated reaction passes through a pH optimum at about 8. The decrease in the rate at higher pH is due to the formation of Zn(ATP) (OH)3-; this species is relatively in­ sensitive towards dephosphorylation. It is concluded that Zn(ATP)2is the reactive species and that the interaction between N (7) and Zn2+ in this complex is crucial for its reactivity. In the presence of 2,2'-bipyridyl (Bipy) the ternary complex, Zn (Bipy) (ATP)2", is formed which is rather stable towards dephosphorylation. It is suggested that the described effects of acceleration and inhibition are helpful for understanding the recycled processes in nature.