Primary structural response in tryptophan residues of Anabaena sensory rhodopsin to photochromic reactions of the retinal chromophore

► Primary protein responses of ASR were investigated for the first time. ► Time-resolved ultraviolet resonance Raman spectra of ASR were observed. ► The photoreaction of ASR is photochromic between two isomers of retinal. ► The spectral changes were observed upon photoreaction starting in both isomers. ► The rates of the structural changes do not depend on the direction of isomerization.