Improved sensitivity in indirect monitoring of chemical shifts of proton-heteronuclear spin pairs (H-1-C-13 and H-1-N-15) in 3D and 4D NMR spectroscopy

In three-dimensional and four-dimensional experiments on doubly labelled pr oteins not only heteronuclear (C-13 or N-15) but also proton (H-1) frequenc ies are often indirectly monitored, rather than being directly observed. In this communication we show how in these experiments by overlaying H-1 and heteronuclear evolutions one can obtain decreased apparent relaxation rates of H-1 signals, yielding improved sensitivity. The new method applies to s pin pairs like H-1-N-15, as in amide groups, or H-1-C-13, as in methine gro ups of alpha or aromatic systems.