A RESONANCE RAMAN-STUDY OF THE C=C STRETCH MODES IN BOVINE AND OCTOPUS VISUAL PIGMENTS WITH ISOTOPICALLY LABELED RETINAL CHROMOPHORES

Previous resonance Raman spectroscopic studies of bovine and octopus r hodopsin and bathorhodopsin in the C-C stretch fingerprint region have shown drastically different spectral patterns, which suggest differen t chromophore-protein interactions. We have extended our resonance Ram an studies of bovine and octopus pigments to the C=C stretch region in order to reveal a more detailed picture about the difference in retin al-protein interactions between these two pigments. The C=C stretch mo tions of the protonated retinal Schiff base are strongly coupled to fo rm highly delocalized ethylenic modes located in the 1500 to 1650 cm(- 1) spectral region. In order to decouple these vibrations, a series of 11,12-D-2-labeled retinals, with additional 13C labeling at C-8, C-10 , C-11 and C-14, respectively, are used to determine the difference of specific C=C stretch modes between bovine and octopus pigments. Our r esults show that the C-9=C-10 and C-13=C-14 stretch mode are about 20 cm(-1) lower in the Raman spectrum of octopus bathorhodopsin than in b ovine bathorhodopsin, while the other C=C stretch modes in these two b athorhodopsins are similar. In contrast, only the C-9=C-10 stretch mod e in octopus rhodopsin is about 10 cm(-1) lower than in bovine rhodops in, while other C=C stretches are similar.