FUNCTIONAL EXPRESSION OF BACTERIORHODOPSIN IN OOCYTES ALLOWS DIRECT MEASUREMENT OF VOLTAGE-DEPENDENCE OF LIGHT-INDUCED H+ PUMPING

We report on the first successful expression of the light driven H+ pu mp, bacteriorhodopsin, into the plasma membrane of oocytes from Xenopu s laevis, The light induced photocurrents which reflect the pumping of H+ by BR were analysed under voltage clamp conditions, At least 100 a ctive BR molecules per mu m(2) were expressed in the plasma membrane s o that both the voltage clamp and giant patch clamp method could be ap plied. We show that H+ pumping by BR is modulated by the membrane pote ntial, i.e. the pump current shows strong voltage dependence in the ra nge measured between -165 mV to +60 mV.