ATP-triggered ADP release from the asymmetric chaperonin GroEL/GroES/ADP7 is not the rate-limiting step of the GroEL/GroES reaction cycle.

The GroEL/GroES protein folding chamber is formed and dissociated by ATP binding and hydrolysis. ATP hydrolysis in the GroES-bound (cis) ring gates entry of ATP into the opposite unoccupied trans ring, which allosterically ejects cis ligands. While earlier studies suggested that hydrolysis of cis ATP is the rate-limiting step of the cycle (t1/2 approximately 10 s), a recent study suggested that ADP release from the cis ring may be rate-limiting (t1/2 approximately 15-20 s). Here we have measured ADP release using a coupled enzyme assay and observed a t1/2 for release of