Fig. 2. Rhodanese is released into the cis cavity following addition of GroES and either ATP or ADP·AlFx to SR1–rhodanese. Binary complexes between urea-denatured, pyrene-labelled rhodanese and SR1 were mixed (1:1) in a stopped-flow apparatus with solutions containing 10 µM GroES and either 3 mM ATP (blue trace), 5 mM ADP (black trace) or 5 mM ADP and AlFx [3 mM KAl(SO4)2 and 30 mM KF] (green trace). The AlFx mixture alone was also mixed (1:1) in the stopped-flow with a solution of preformed SR1–rhodanese-GroES–ADP complex (red trace). The anisotropy of the pyrene label, reflecting the mobility of the polypeptide and its release from the cavity walls, was monitored as a function of time after mixing. Traces represent summations of 10−15 runs.