Fig. 3.

¹³Cζ chemical shifts of Tyr136^3.51, Tyr223^5.58, and Tyr306^7.53 in rhodopsin and Meta II. Difference spectra obtained between rhodopsin (black line) and Meta II (red line) for the three tyrosine mutants: Y306F, Y223F, and Y136F. The difference spectra are taken between the wild-type protein and the mutant in order to reveal the frequency of the ¹³Cζ resonance. Tyr223^5.58 and Tyr306^7.53 both exhibit downfield changes in chemical shift between rhodopsin and Meta II. The ¹³Cζ chemical shift of Tyr136^3.51 is not appreciably altered upon conversion to Meta II.