Electric signals associated with the photocycle of bacteriorhodopsin

Flash-induced biphasic fast electric signals from bacteriorhodopsin (BR) in the purple membrane (PM) of ffalobucterium halobium were first observed in [l-3]. The observations were made on model systems: PM in thick planar lipid membranes [ 11, and a not well-characterized interfacial layer of PM built into foam apposed to a thin teflon septum [2,3]. Here we report the measurement of the electric signal on untreated PM suspension (their orientation was achieved by means of an electric field [4] ), the existence of at least two long-living components, and the simultaneous measurement of the transiently liberated protons. Additional measurements of the time constants of the changes in light absorption rendered possible the unambiguous designation of the components of the electric signals to the intermediates of the BR photocycle. Similar measurements in a heavy water suspension demonstrated that the complex electric signal reflects the translocation of proton or deuteron in BR. We suggest that the complex electric signal be designated as a protein electric response signal (PERS).