Extended Data Fig. 9. Spectroscopic characterization of wild-type GtACR1 and the D234N mutant.

a, Absorption spectra of wild-type GtACR1 (top left) and the D234N mutant (top right) measured from pH 3.0 to 10.0. The λ_max value at each pH is listed in the table (bottom). b, Difference FTIR spectra of wild-type GtACR1 and the D234N mutant measured at 77 K, 170 K and 200 K. c, Difference FTIR spectra of wild-type GtACR1 in the 1,690–1,770 cm⁻¹ region measured at pH 5.0, 7.0 and 9.0. Forty identical recordings at 77 K and seven identical recordings at 170 K and 200 K were averaged.