The measurement of homo- and heteronuclear coupling constants in proteins have been largely performed from 2D and 3D E.COSY (Exclusive COrrelation SpectroscopY) ( 85JACS6494 , 86JCP6837 , and 87JMR474-75 ) experiments in which the coupling between two nuclei A and B (B is the so-called passive spin) is measured from the relative displacement of the two resolved components of an AC cross-peak, which are displaced in one-dimension of the nD spectrum by a large one-bond J(AB) coupling constant and in the other dimension by the desired small long-range J(BC) coupling constant ( 96ENC1473 ).