Spectral dimorphism of crayfish visual pigment in solution

Crayfish (Procambarus) photoreceptor membranes were prepared by a new technique. Digitonin extracts made at 0 degrees contain two rhodopsin-like pigments, P562 and P512, in a ratio of about 5:4. On exposure to light at 10 degrees C, P562 is converted to a metarhodopsin-like photoproduct with lambda max at 515 nm (M515), and P512 is converted to a metarhodopsin-like photoproduct with lambda max at 475 nm (M475). When warmed to 22 degrees C, both photoproducts bleach in minutes to retinal and opsin. Neither P562 nor P512 is attacked by hydroxylamine, but both are destroyed by the detergent Ammonyx LO and by reduction of disulfide bridges with 2-mercaptoethanol. Neither is altered by changing the concentration of Cl-. P562 is more susceptible than P512 to thermal denaturation and attack by OH-, and its spectrum is distinctly narrower than predicted by an Ebrey-Honig nomogram. P562 and P512 do not interconvert, either in the dark or in the presence of light. P512 is distinct from M515; it is substantially more stable at 22 degrees C and has a 23% smaller molar extinction coefficient. On the other hand, M515 is spectrally very similar to the single metarhodopsin that is formed by irradiation of rhabdoms from dark-adapted crayfish. As neither P562 nor P512 is found by irradiation of rhabdoms from dark-adapted crayfish. As neither P562 nor P512 is found in crayfish rhabdoms, we conclude that both pigments are created in digitonin micelles from a spectrally and kinetically homogeneous population of rhodopsin molecules with lambda max near 530 nm in the rhabdom.