Fig. 5.

Populations and ¹³C12 chemical shifts of L substrates. (A) Volumes of the ¹⁵Nζ-C15 peaks of the mixture formed by direct red light irradiation of bR₅₆₈ at 150 K and of the mixture formed by subsequent thermal relaxation at 170 K. All L's except L₁₈₆ revert to bR₅₆₈ and thus are shunt states. Note that because cross-polarization efficiencies vary among the different intermediates, the intensity changes are nonstoichiometric. (B) Evolution of the retinal ¹³C12 chemical shift through the various photocycle intermediates. Filled symbols represent functional states, and open symbols represent shunt (i.e., L₁₆₆, L₁₇₄, and L₁₈₁) states. The squares represent data from previous work (12, 28). Note that the steric interactions at C12 that are typical of the middle and late photocycle are achieved already in the functional form of L.