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

The influence of solubilization on the dark adaptation kinetics and sp ectral changes associated with the light- to dark-adapted transition o f monomeric bacteriorhodopsin was studied and compared with that of th e purple membrane. The kinetics of dark adaptation were described with a two-state model. An analysis of the temperature dependence of the r ate constants yielded the activation enthalpy and entropy of the trans ition. The results show that solubilization affects the energetics of the light to dark transition. A decrease in the activation entropy res ults 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 temperat ure, which can be explained by the temperature dependence of the absor bance.