pD dependence of HDX rates for the C-2 proton in TM68 (A), TM65 (B), and TM85 (C) measured by NMR. Lines represent exponential decay functions. Chemical structures are shown on the right. D) The observed rate of exchange (kex) for compounds TM85 (blue), TM68 (red), and TM65 (purple) as a function of pD. The slope of each line (m) is indicated next to the linear fit. E) The rate of exchange for compounds TM85 (blue), TM68 (red), TM65 (purple), TM39 (brown), TM31 (gray), TM91 (Black) at pD 7.0 as a function of C-2 chemical shift (ppm). Error bars show standard deviations from triplicate measurements.