Figure 4.

One-dimensional ¹³C MAS NMR spectra of rhodopsin and Meta I. Rhodopsin was regenerated with 11-cis retinal selectively ¹³C labeled at different carbons along the polyene chain and the β-ionone ring. Overlap of the ¹³C MAS NMR spectra of rhodopsin (black) and Meta I (orange) shows that most of the retinal resonances broaden considerably in Meta I as compared to the sharp narrow resonances observed in rhodopsin and Meta II (red). There is nearly complete conversion of rhodopsin to Meta I. For example, the ¹³C9 retinal resonance in rhodopsin falls in an uncrowded region of the spectrum. The residual intensity of the ¹³C9 resonance in the Meta I spectrum is <10% of its original intensity in rhodopsin. Also, there is <10% conversion of rhodopsin to Meta II. For example, the spectra of Meta I containing ¹³C13-labeled retinal show a complete absence of a resonance associated with Meta II.