PICOSECOND FLUORESCENCE SPECTROSCOPY OF THE PURPLE MEMBRANE OF HALOBACTERIUM-HALOBIUM IN ALKALINE SUSPENSION

The fluorescence lifetime of the light-adapted purple membrane of Halo bacterium halobium in alkaline suspension was measured with a femtosec ond-pulse laser-synchroscan streak camera system (< 10 ps resolution t ime, 620 nm excitation) at 22 degrees C. The lifetimes of slow, fast a nd very fast decay components were found to be 62 +/- 2, 9 +/- 2 and < 1 ps, respectively. The fastest component is attributed to bacteriorh odopsin (bR(568)). We examined the effect of pH and excitation power o n the amplitude of the slow component and concluded that its origin is attributable to the Q intermediate, which is a photoproduct of the N intermediate formed in the later stage of the photocycle of bR(568). W e found that Q is the same species as pseudo-bacteriorhodopsin (p-bR).