The role played by pentacovalent intermediates in the sequence of stages of the hydrolysis of 5′-ATP with metal ions

The earlier developed model of irreversible hydrolysis of 5′-ATP catalyzed by the main metal ion Cu²⁺ was used to consider the influence of additional metal ions on the deactivation of active centers conjugated with hydrolysis. It was assumed that conjugation in enzymes occurred through a sequence of stages including the formation of pentacovalent intermediates at early hydrolysis stages and their subsequent slow pseudorotation with the participation of the γ phosphorus atom of the pentacovalent intermediate. From this standpoint, the formal kinetic laws of the hydrolysis of Mg·ATP were analyzed for two enzymes, luciferase from fireflies and nitrogenase Azotobacter vinelandii. The roles played by Mg²⁺ OH⁻ ion formation with the participation of external OH⁻ ions and the selective hydration of intermediate hydrolysis products by a coordinated water molecule of the second metal ion, including the transition metal ion participating in hydrolysis, were considered.