The T 1 and T 2 relaxation data were processed and analyzed using Bruker Dynamic Center software (version 2.7.2). For the analysis of hetNOE spin relaxation times, peak heights were determined by TopSpin software from spectra with and without NOE. To determine the errors for hetNOEs, signal to noise ratio was first determined from the region without any peaks, and the limiting extremes of the noise values were then added to or subtracted from the peaks to estimate the largest effect of noise to the ratio between the peaks in the two spectra.