Bacteriorhodopsin

Halobacterium halobiumResides in hypertonic environments (shallow waters of San Francisco bay)Diatomic oxygen is plentiful = OXPHOSDiatomic oxygen unavailable = LIGHT HARVESTINGAchieved by Bacteriorhodopsin, a 26 KD protein with all-trans-retinal attachedLIGHT IS CONVERTED DIRECTLY INTO A H+ MOTIVE FORCEF0F1 ATPaseH++ + + + + + + - - - - - - - - - H+ATPhv

Retinal is bound to LysineH+ pumping

PhotocycleThe energy trapping conformational transition occurs within one psDeprotonation and reprotonation steps are characterized by intermediates which contain distinct absorption spectraOne full turn of the cycle occurs within a msHence each step has a characteristic colourEvery sec, 50 protons are exportedOne question remainshow does the light induced isomerization of this protein drive H+ translocation

Bacteriorhodopsin is a Dynamic, Transmembrane ProteinSeveral transmem spanning helices3 Tyr hold the BR in placeRetinal sits at the junction separating the twohalf channels Notice the Bacteriorhodopsin is surrondedby Asp and Arg

Aspartate and Arginine are involved in the translocation process