The purpose of this study on photoreception of modified bacteriorhodopsins involves obtaining information on the structure of the protein by chemically analyzing bacteriorhodopsins which are reconstituted with artificial retinals and the opsin, and by comparison of their properties with these of the native bacteriorhodopsin. We report structural contribution of the protein to the bathochromic shifts and photochemical behavior of artificial bacteriorhodopsin. 1) Hydroretinals and hydrorhodopsins were synthesized to investigate the protein circumstances. 'Opsin shift', one of the indicator, was defined as λ_<max> of the protonated Schiff base of n-butylamine minus λ_<max> of the corresponding pigment (cm^<-1>). Point charge model was proposed that another anion except a counter ion of the Schiff base would be located not on the side chain but near the cyclohexene ring. 2) Modification of cyclohexene ring to phenyl ring strongly affected the opsin shift, while introduction of bromine atom to side chain was less effective. 3) Irradiation upon bacteriorhodopsin involving Np-retinal gave rise to anomalous photoisomerization of retinal moiety.
