The maximum photosteady state fraction of K, x K max , and the ratio of the quantum yields of the forward and back light reactions, trans‐bacteriorhodopsin (bR) hArr; K, φ bR /φ K , were obtained by measuring the absorption changes produced by illumination of frozen water‐glycerol (1:2) suspensions of light‐adapted purple membrane at different wavelengths at ‐165°C. An independent method based on the second derivative of the absorption spectrum in the region of the β‐bands was also used. It was found that The quantum yield ratio (0.66 ± 0.06) was found to be independent of excitation wavelength within experimental error in the range510–610 nm. The calculated absorption spectrum of K has its maximum at603–606 nm and an extinction 0.85 ± 0.03 that of bR. At shorter wavelengths there are P‐bands at 410, 354 and 336 rim. Using the data of Hurley et al. (Nature 270,540–542, 1977) on relative rates of rhodopsin bleaching and K formation, the quantum yield of K formation was determined to be 0.66 ± 0.04 at low temperature. The quantum efficiency of the back reaction was estimated to be 0.93 ± 0.07. These values of quantum efficiencies of the forward and back light reactions of bR at ‐ 165°C coincide with those recently obtained at room temperature. This indicates that the quantum efficiencies of both forward and back light reactions of bacteriorhodopsin are temperature independent down to ‐165°C.
No takes yet. Share an insight, caveat, or question.
Balashov et al. (1991) studied this question.