VISUAL PIGMENT ABSORPTION OF PHOTORECEPTORS AND SPECTRAL SENSITIVITY OF RETINA OF ELEDONE MOSCHATA

1. The extinction spectrum of Eledone moschata rhodopsin is very similar to that of Octopus. The α-peak was at 470 nm and the β-peak at ∼ 380 nm. 2. Neither white nor monochromatic light was capable of bleaching the visual pigment under physiological pH and temperature conditions. Continuous illumination produces a mixture of rhodopsin, acid metarhodopsin (M I, λmax 516 nm) and alkaline metarhodopsin (M II, λmax 380 nm). The ratio of concentrations of the three pigments remains constant even after illumination. The ratio depends upon the wavelenght of the irradiation and the pH of the solution. 3. The relative quantum efficiency for the reconversion of acid metarhodopsin to rhodopsin is approximately one for irradiation with 438 nm. 4. Absorption measurements on the irradiated receptor itself show that a pigment mixture develops within the receptor depending upon the wavelength of the adapting light. 5. Spectral sensitivity curves determined electrophysiologically are in good agreement with the extinction curve of rhodopsin. Small differences occur at higher quantum levels. Different sensitivity curves were also recorded with mikroelectrodes in deeper layers of the receptor. 6. The concentration of visual pigment within the receptor is very high. The extinction in a receptor 100 μ. long lies between 0,75 and ∼ 2 at the absorption maximum of 470 nm. 7. Because of the high rhodopsin concentration in the receptor, the mixture of rhodopsin and its intermediates functions as a screening pigment for the deeper tubuli layers. 8. The screening effect is treated theoretically. 9. The deviations (cf. point 5) of the spectral efficiency curves from the extincion curve of rhodopsin can be explained by the hypothesis in connection with the screening effect. © 1968 Springer-Verlag.