Energetics and chronology of phototransients in the light response of the purple membrane of Halobacterium halobium.

Arrhenius parameters for formation and decay of phototransients in suspensions of purple membrane fragments in H2O and 2H2O have been determined in the temperature range 0-60 degree C. Kinetic isotope effects are found which show that proton transfer steps are involved in both formation and decay of the two longest-lived transients absorbing at 410 nm and 660 nm, respectively. The results also suggest that these transients do not occupy a single pathway in the spontaneous deexcitation of bacteriorhodopsin within the purple membrane. Purple membrane undergoes a phase transition at 25-30 degrees C in both H2O and 2H2O.