title: Studies on cephalopod rhodopsin: photoisomerization of the chromophore.
abstract: Photoisomerization of the chromophore of squid rhodopsin is dependent upon the irradiation temperature. Above 0 degrees C, only 11-cis in equilibrium all-trans reaction proceeds and the all-trans leads to 9-cis reaction is limited to extremely low efficiency. At liquid nitrogen temperature, 11 cis in equilibrium all-trans in equilibrium 9-cis reaction takes place. At intermediary low temperatures (-80 degrees C to -15 degrees C) another isomer of retinal may be produced by the irradiation, which forms a pigment having an absorbance maximum at 465 nm (P-465). The formation of P-465 decreases remarkably in the narrow temperature range from -30 degrees C to 0 degrees C where mesorhodopsin converts to metarhodopsin. Medsorhodopsin is quite different from metarhodopsin in the photoisomerization of the chromophore because P-465 is produced from the former but not from the latter. No P-465 is produced both at liquid nitrogen temperature and above 0 degrees C. P-465 is more labile than any of the other photoproducts so far known, that is isorhodopsin, alkaline and acid metarhodopsins. P-465 is converted to metarhodopsin by irradiation.
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D049832:Decapodiformes; D007536:Isomerism; D008433:Mathematics; D010777:Photochemistry; D011487:Protein Conformation; D012168:Retinal Pigments; D012243:Rhodopsin; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
chemical_list: D012168:Retinal Pigments; D012243:Rhodopsin