Recovering lost magnetization: polarization enhancement in biomolecular NMR.

Experimental sensitivity remains a major drawback for the application of NMR spectroscopy to fragile and low concentrated biomolecular samples. Here we describe an efficient polarization enhancement mechanism in longitudinal-relaxation enhanced fast-pulsing triple-resonance experiments. By recovering undetectable (1)H polarization originating from longitudinal relaxation during the pulse sequence, the steady-state (15)N polarization becomes enhanced by up to a factor of ~5 with respect to thermal equilibrium yielding significant sensitivity improvements compared to conventional schemes. The benefits of BEST-TROSY experiments at high magnetic field strength are illustrated for various protein applications, but they will be equally useful for other protonated macromolecular systems.