Figure 2.

Illustration of the procedure used to prepare samples for NMR analysis of amide exchange rates of GroEL-bound DHFR. The top ring of GroEL is shown as a cross-section. Amide protons protected from exchange are labeled as “H,” while those which exchange with solvent deuterons are labeled as “D.” After each of 10 time points, DHFR is refolded to the native state from which further exchange is negligible, separated from GroEL, and placed in an NMR spectrometer to measure the proton occupancy of each amide.