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. Author manuscript; available in PMC: 2020 Jul 13.
Published in final edited form as: J Am Chem Soc. 2019 Jan 14;141(4):1735–1741. doi: 10.1021/jacs.8b12493

Figure 5.

Figure 5.

(a) UV–vis spectra of M1-L121Q before and after irradiation with green light, showing a high/low pKa system where green light irradiation leads to decreased PSB and increased SB absorption. (b) Overlay of the all-trans-retinal-bound M1-L121Q imine before (green carbons) and after (salmon carbons) laser irradiation at 532 nm, clearly showing the Gln121 movement. The all-trans retinal bound M1-L121Q structure features a direct hydrogen bond between the nitrogen atom of the imine and Gln121 (3.0 Å). Laser irradiation (532 nm) of crystals does not result in the isomerization of any bonds; however, L121Q swings away from the imine (now ~4.7 Å), leading to the low pKa form of the imine and SB formation.