Absorption and spectral sensitivity of isolated rod outer segments regenerated with 11-cis 4-OH retinal is blue shifted in respect to rods containing native visual pigment. (A) Absorption spectra of native dark-adapted rod photoreceptor visual pigment (λmax = 509 nm, n = 7) and of pigment regenerated with 11-cis 4-OH retinal (λmax = 478 nm, n = 7) measured microspectrophotometrically in intact outer segments. (B) Normalized spectral sensitivity recorded from rods in the native dark-adapted state (n = 5) and after bleach and regeneration with 11-cis 4-OH retinal (n = 7). The lines represent the normalized absorbance of native dark-adapted rod photoreceptor visual pigment (dashed line) and of 11-cis 4-OH retinal (continuous line). (C) The blue-shifted 4-OH rhodopsin (n = 4) has a lower level of dark noise power than native rhodopsin (n = 4) as can be seen in the plot of power spectral density. This is caused by the higher activation energy that follows from shorter wavelength absorption. Instrumentation noise that was recorded with the cell in the electrode and in the presence of bright saturating light is indicated by the dotted line. The retinal concentration in the experiment was 10 µM in 0.1% ethanolic solution. Data points are plotted ± SEM in all graphs.
