Ionochromic Behavior of Gecko Visual Pigments

Digitonin extracts of the retina of Gekko gekko prepared to minimize the presence of chloride ions show the photopigment to be at about 490 nanometers rather than at 521 nanometers, the position found for the same pigment in situ. The addition of chloride to the extract causes a bathochromic shift in spectral absorbance, the magnitude of the shift being related to the concentration of chloride, within limits. The effect is a specific one, and of all the anions tested only bromide causes a similar bathochromic shift. The nature of the cation is not involved since the same action is produced by the chlorides of sodium, lithium, potassium, rubidium, cesium, calcium, magnesium, beryllium, lanthanum, and choline.