Resonance Raman spectra of octopus acid and alkaline metarhodopsins

The resonance Raman spectra of acid and alkaline metarhodopsins of octopus were measured. The acid metarhodopsin exhibited the Schiff base C = N stretching band at 1655 cm-1 in H2O and at 1625 cm-1 in 2H2O, and therefore the Schiff base is shown to be protonated. The C = C stretching band was observed at 1548 and 1572 cm-1 for acid and alkaline metarhodopsins, respectively. Other Raman lines of octopus acid metarhodopsin were assigned from the data of Cookingham et al. (Cookingham, R.E., Lewis, A. and Lemley, A.T. (1978) Biochemistry 17, 4699-4711). Frequencies of some structure-sensitive Raman lines differed among octopus, squid and bovine metarhodopsins; such differences may be important in interpreting the presence of optical activity in octopus metarhodopsins but its absence in squid metarhodopsins.