ABSORPTION SPECTRA OF TCA-DENATURED RHODOPSIN AND OF A SCHIFF BASE COMPOUND OF RETINAL

Abstract— When TCA-denatured rhodopsin was frozen in liquid nitrogen, Λ_max was markedly shifted to longer wavelengths as the concentration of TCA increased. After TCA denaturation, species specific absorption disappeared and the absorption maxima of the squid pigments became identical with those of corresponding pigments of octopus.
In solutions at 5° the bathochromic shift of Λ_max of TCA denatured rhodopsin was observed at higher concentrations of TCA than in the frozen state. Λ_max of N-retinylidene-butylamine (NRB) was also displaced towards longer wavelengths with increasing concentrations of TCA. This bathochromic shift was enhanced by freezing. The mode of the bathochromic shift of Λ_max provoked by TCA was very similar both in the cases of denatured rhodopsin and of NRB. The absorption spectrum of NRB was identical in shape with that of TCA-denatured rhodopsin, as the half-band widths of both materials were about 5500 cm^-1 in the liquid state and 5000 cm^-1 in the frozen state. Λ_max of retinal and NRB were red shifted in polar and polarizable solvents.
It was concluded that the strong acidity and the relatively large polarizability of TCA are responsible for the bathochromic shift of Λ_max of the Schiff base in TCA-denatured rhodopsin.