Spectroscopic analyses of K296G pigments. a, difference spectra of K296G pigments purified in DM; nPrSB (red), EtSB (green), and MeSB (yellow) relative to the wild type (blue). The inset shows the absolute spectra of K296G/nPrSB (red) purified in CHAPS/PC. b, photosensitivities of K296G pigments relative to the wild-type rhodopsin. The error bars represent the deviation from two independent measurements, and the blue dotted line represents the photosensitivity of the wild type. c, difference spectra of acid denaturation of K296G pigments relative to the wild type. The inset shows the absolute spectra for K296G/nPrSB (red). The addition of acid produced a denatured pigment with a peak at 437 nm. The pH after adding the acid was <1.5. Denaturation of the wild type (blue) is shown for comparison.