Cobalt(III)-promoted hydrolysis of atp

Abstract

The rate of phosphate hydrolysis of ATP in the substitution-inert complex Co(NH 3) 4ATP-has been examined in the presence and absence of [Co(cyclen)(H 2O) 2] 3+. The rate of hydrolysis of Co(NH 3) 4ATP- in the absence of [Co(cyclen)(H 2O) 2] 3+ is essentially independent of pH in the range 6.0 to 9.0, and the rate constant is 2.6 × 10 −5 sec −1 at pH 9.0, 40°C, and 1.0 M ionic strength Rate constants for the hydrolysis of Co(NH 3) 4ATP- in the presence of [Co(cyclen)(H 2O) 2] 3+ are sharply dependent upon pH in the same range. The rate constants at pH 8.0, 8.6, and 9.0 are 8, 63, and 95 times larger than the rate constant at pH 7.0. At pH 9 the rate constant is 1.2 × 10 −3 sec −1 for 16 mM Co(NH 3) 4ATP- in the presence of 10 mM [Co(cyclen)(H 2O) 2] 3+. The proposed mechanism for hydrolysis involves the coordination of a phosphate group of Co(NH 3) 4ATP- by [Co(cyclen)(H 2O) 2] 3+ to form a dinuclear species, followed by internal attack of coordinated hydroxide on the phosphate chain.