Photoreactions of retinochrome at very low temperatures

AbstractRetinochrome is one of the retinal proteins found in the retina of cephalopods. It catalyses the light isomerization of retinal from the all-trans to the 11-cis form. On cooling to 25 K, the absorption peak of retinochrome (λmax 490 nm) was broadened with a shoulder, showing the spectrum steepened on the long wavelength side. On irradiation with yellow-green light (550 nm), retinochrome produced an intermediate with λmax at a shorter wavelength, around 465 nm, and a lower extinction coefficient than lumiretinochrome. It changed to lunuretinochrome (λmax 475 nm) in the dark on warming to liquid nitrogen temperature. We shall call this new intermediate prelunuretinochrome