Effect of pH on the photoreaction cycles of bacteriorhodopsin

Photoreaction cycles of acidified bacteriorhodopsin (bR acid 605 ) at room temperature was studied by nanosecond and picosecond spectroscopy. A precursor of bathobacteriorhodopsin was found to be converted to bathobacteriorhodopsin within 30 ps. Spectra and formation times of batho‐ and lumibacteriorhodopsin are identical to those of bacteriorhodopsin in neutral suspension. However, lumibacteriorhodopsin lifetime is > 700 μs and the formation of metabacteriorhodopsin was not observed in low pH suspension. Thus, the decay process of lumibacteriorhodopsin plays an important role in the proton pump action.