Conventional sequential assignment of unlabeled proteins makes use of COSY and TOCSY experiments to delineate spin systems by means of through-bond connectivities via J_HH, and NOESY experiments to identify through-space ¹H-¹H NOE connectivities. For larger proteins isotopically labeled with ¹⁵N and/or ¹³C, an alternative is based on the largest one-bond heteronuclear (¹J_XY) coupling constants.     The main advantages of such approach are:

• Less time is required to transfer magnetization (avoids magnetization loss due to T₂ relaxation)
• The one-bond couplings are relatively uniform, depend only weakly on conformation, and are significantly larger than the line widths.
• An increased number of strategies are available, including all heteronuclei.
• More NMR data can be used to improve structure refinement.

    The approximate ¹J_XY values which are essential for the assignment procedure by triple resonance NMR experiments in isotopically enriched proteins can be summarized as:

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