Overlay of ssNMR spectra of [1′-13C, 4′-15N, 9-13C]ImmH and hPNP–[1′-13C, 4′-15N, 9-13C]ImmH–PO4 complex. Chemical shifts are referenced to the chemical shift of adamantine set to 40.5 ppm. The peaks at 108.6 and 104 ppm correspond to the 9-13C label in bound and free ImmH, respectively. The peaks at 62.9 and 54.0 correspond to the 1′-13C label in bound and free ImmH, respectively.