| Abstract: | Abstract —A photoresponsive pigment, described previously as the photoreceptor pigment for phototaxis in Dictyostelium discoideum, was examined by low-temperature spectroscopy. The absorption spectrum of the purified pigment frozen in darkness indicates the reduced form of a high-spin heme protein, and the spectrum of the pigment frozen during irradiation (to freeze in the photoproduct) indicates the oxidized form of the heme protein. The light-induced absorbance changes measured at room temperature also indicate photooxidation of a heme pigment. The action spectrum for the light-induced absorbance change shows a primary peak at about 430 nm and a broad, less active maximum in the 550–580 nm region. The absorption spectrum of the reduced pigment and the action spectrum for its photooxidation are both similar to the action spectrum for phototaxis of the pseudoplasmodia of D. discoideum. |
