References:
L.E. Kay, M. Ikura, R. Tschudin and A. Bax (1990) J. Magn. Reson. 89 496-514. (Link to Article)
B.T. Farmer II, R.A. Venters, L.D. Spicer, M.G. Wittekind and L. Müller (1992) J. Biomol. NMR 2 195-202. (Link to Article)
S. Grzesiek and A. Bax (1992) J. Magn. Reson. 96 432-440. (Link to Article)

Minimum labelling: ¹⁵N, ¹³C

Dimensions: 3

Here the magnetisation is passed from ¹H to ¹⁵N and then via the N-Cα J-coupling to the ¹³Cα and then back again to ¹⁵N and ¹H hydrogen for detection. The chemical shift is evolved for ¹H^N as well as the ¹⁵N^H and ¹³Cα, resulting in a 3-dimensional spectrum. Since the amide nitrogen is coupled both to the Cα of its own residue and that of the preceding residue, both these transfers occur and peaks for both Cαs are visible in the spectrum. However, the coupling to the directly bonded Cα is stronger and thus these peaks will appear with greater intensity in the spectra.

This experiment can be useful for backbone assignment when used in conjunction with the HN(CO)CA, HNCO and HN(CA)CO if the CBCANNH and CBCA(CO)NNH spectra are of bad quality.

By overlaying the HN(CO)CA spectrum with the HNCA, it becomes even easier to identify and distinguish between all Cα_i and Cα_i-1 peaks.