PHOTOACTIVITIES OF THE RED-SHIFTED AZULENIC BACTERIORHODOPSIN ANALOGS

Incorporating red-shifted retinal analogues, such as azulenic retinals , into bacterioopsin provides a method to evaluate the low-energy limi t for bacteriorhodopsin (bR) proton-pumping activity. We report result s of nanosecond time-resolved studies of three azulenic bR analogues. In contrast to a recent report on an azulenic bR analogue (Druzhko et al., 1996),(4) we conclude that such pigments do not exhibit photocycl es (no detectable intermediates) and suspect that the preferred direct ion of deactivation is internal conversion to the low-lying forbidden S-1 state of the azulene chromophore. We further demonstrated that fur slow-binding bR analogues, the samples can easily be contaminated wit h small amounts of native bR.