Abstract
The temperature dependence of regeneration of bacteriorhodopsin (bR) from its apoprotein, bacterio-opsin (bO), and all-trans retinal was investigated using two different procedures to probe the structural properties of bO at high temperatures. Regeneration experiments performed at 25 °C after incubation of bO within the temperature range of 35–75 °C indicate that irreversible thermal unfolding begins at 50 °C. When bO is incubated for one hour and mixed with retinal at the same elevated temperatures, however, a greater extent of regeneration to bR occurs, even at temperatures ranging from 50 to 65 °C. These experimental results indicate that regeneration of bR occurs from thermally unfolded bO and suggest dynamic structural fluctuation of bO in the unfolded state.
