2.3. NMR spectroscopy
Nuclear magnetic resonance (NMR) measurements on unlabeled
samples were performed at pH 3.3 and 5.1, using 2 mM protein
solutions in 20 mM sodium phosphate buffer containing 10%
of 2H2O. NMR experiments were carried out at 500 MHz, on a Varian
Unity 500 spectrometer using standard acquisition programs.
Mono-(1D) and two-dimensional (2D) spectra were accumulated
with a spectral width of 6493 Hz and were acquired at 35 C. 2D
TOCSY experiments were recorded with a mixing time of 70 ms
and the water suppression was achieved by DPFGSE sequence.
Typically, 65 transients of 2 K data points
were collected for each of the 256 increments; the data were zero
filled to 1 K in x1. Data were processed and analysed using
NMRpipe and Sparky software.