CIRCULAR-DICHROISM OF RHODOPSINS AND PORPHYROPSINS

Circular dichroism (CD) and absorption spectra were determined for digitonin extracts of 3 rhodopsins: cattle [Bos taurus], grass frog [Rana pipens] and pigeon [Columba livia]; and 3 porphyropsins: channel catfish [Ictalurus punctatus], bluegill sunfish [Lepomis macrochirus], and redear sunfish [Lepomis microlophos]. Porphyropsins, like rhodopsins, exhibited 2 positive CD peaks in the spectral region 320-700 nm: an .alpha. peak at about 520 nm and a small .beta. peak at about 355 nm. These peaks substantially diminished upon bleaching. In the CD spectra the .alpha. peaks of the porphyropsins were larger than the .alpha. peaks of the rhodopsins, while the .beta. peaks were smaller than those of the rhodopsins. This was just the opposite of the corresponding relationship between the peaks in the absorption spectra. The maxima of these peaks in the CD spectra of rhodopsins and porphyropsins were consistently blue-shifted from the corresponding maxima in absorption spectra. Some of the visual pigments showed additional positive CD peaks in the spectral region 250-320 nm. In all the visual pigments studied, the CD spectra in this region decreased on bleaching. No reciprocal relationship was observed between any of the CD bands in the visible and near UV region of the spectrum.