DARK-ADAPTATION AND SPECTRAL CHANGES IN TRITON-X-100-TREATED BACTERIORHODOPSIN

The influence of solubilization on the dark adaptation kinetics and spectral changes associated with the light- to dark-adapted transition of monomeric bacteriorhodopsin was studied and compared with that of the purple membrane. The kinetics of dark adaptation were described with a two-state model. An analysis of the temperature dependence of the rate constants yielded the activation enthalpy and entropy of the transition. The results show that solubilization affects the energetics of the light to dark transition. A decrease in the activation entropy results in a significantly smaller dark adaptation rate in the monomeric form. The blue shift of the visible band associated with the light to dark transition of monomeric bacteriorhodopsin depends on the temperature, which can be explained by the temperature dependence of the absorbance.