Figure 7.

Enhancement of ¹⁵N signals in a ¹⁵N-labeled polypeptide lysate with molecular weight cut-off of 10kDa, via polarization transfer from hyperpolarized water. (a) ¹⁵N NMR spectra arising from 90° ¹⁵N pulses applied over the indicated post-dissolution times, reflecting the 17.9 sec T₁ we detect for the water protons onto the ¹⁵N signals enhanced by the exchangeable protons. The sum of six consecutive scans from this time series are displayed. (b) Sum of first 15 scans (upper trace) following the injection of hyperpolarized water, compared vs a thermal equilibrium ¹⁵N spectrum (middle trace), measured by signal averaging 10000 scans over the course of ca. 40 hours. The difference between these spectra is displayed in the bottom trace, highlighting the over-enhancement of the arginine side-chains (NH₂) and lysine’s (NH₃) groups, and the under-enhancement of the proton-less proline backbone nitrogens. The average signal enhancement of the ¹⁵N backbone amides is >500× relative to ¹⁵N thermal equilibrium signal. Other acquisition parameters are as in Figure 5.