Adenosine 5′-O-(3-thio)triphosphate (ATPγS) is a substrate for the nucleotide hydrolysis and RNA unwinding activities of eukaryotic translation initiation factor eIF4A

Minimal kinetic and thermodynamic schemes for the eIF4A-catalyzed hydrolysis of ATP•Mg (A) and ATPγS•Mg (B). K_M values were determined in independent experiments, except underlined values that were calculated based on the thermodynamic cycles shown. K_M values are believed to directly reflect the equilibrium dissociation constants for RNA and nucleotide binding (Lorsch and Herschlag 1998a). Unbound ligands are not depicted for clarity. E•ADP•inorganic phosphate (or inorganic thiophosphate)•RNA complexes are not depicted because is appears that eIF4A has low affinity for inorganic phosphate, and this ternary complex has not been observed (Lorsch and Herschlag 1998a).